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Versions: (draft-coffin-sacm-nea-swid-patnc) 00 01 draft-ietf-sacm-nea-swima-patnc

SACM                                                          C. Schmidt
Internet-Draft                                                 D. Haynes
Intended status: Standards Track                               C. Coffin
Expires: September 14, 2017                        The MITRE Corporation
                                                           D. Waltermire
                          National Institute of Standards and Technology
                                                     J. Fitzgerald-McKay
                                                   Department of Defense
                                                          March 13, 2017


      Software Inventory Message and Attributes (SWIMA) for PA-TNC
                   draft-ietf-sacm-nea-swid-patnc-01

Abstract

   This document extends the PA-TNC specification [RFC5792] by providing
   specific attributes and message exchanges to allow endpoints to
   report their installed software inventory information to a NEA server
   (as described in [RFC5209]).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 14, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Network Endpoint Assessment (NEA) . . . . . . . . . . . .   5
     1.2.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.3.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   7
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.1.  Supported Use Cases . . . . . . . . . . . . . . . . . . .   8
       2.1.1.  Use Software Inventory as an Access Control Factor  .   8
       2.1.2.  Central Stores of Up-to-Date Endpoint Software
               Inventory Data  . . . . . . . . . . . . . . . . . . .   9
       2.1.3.  PA-TNC Use Cases  . . . . . . . . . . . . . . . . . .   9
     2.2.  Non-supported Use Cases . . . . . . . . . . . . . . . . .   9
     2.3.  Specification Requirements  . . . . . . . . . . . . . . .  10
     2.4.  Non-Requirements  . . . . . . . . . . . . . . . . . . . .  12
     2.5.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .  12
     2.6.  Non-Assumptions . . . . . . . . . . . . . . . . . . . . .  12
   3.  System Requirements . . . . . . . . . . . . . . . . . . . . .  12
     3.1.  Data Sources  . . . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Data Models . . . . . . . . . . . . . . . . . . . . . . .  14
     3.3.  Basic Attribute Exchange  . . . . . . . . . . . . . . . .  15
     3.4.  Core Software Reporting Information . . . . . . . . . . .  16
       3.4.1.  Software Identifiers  . . . . . . . . . . . . . . . .  16
       3.4.2.  Data Model Type . . . . . . . . . . . . . . . . . . .  17
       3.4.3.  Record Identifiers  . . . . . . . . . . . . . . . . .  18
       3.4.4.  Software Locators . . . . . . . . . . . . . . . . . .  18
       3.4.5.  Source Identifiers  . . . . . . . . . . . . . . . . .  19
       3.4.6.  Using Software and Record Identifiers in SW
               Attributes  . . . . . . . . . . . . . . . . . . . . .  20
     3.5.  Targeted Requests . . . . . . . . . . . . . . . . . . . .  21
     3.6.  Monitoring Changes in an Endpoint's Software Inventory
           Evidence Collection . . . . . . . . . . . . . . . . . . .  22
     3.7.  Reporting Change Events . . . . . . . . . . . . . . . . .  24
       3.7.1.  Event Identifiers . . . . . . . . . . . . . . . . . .  25
       3.7.2.  Core Event Tracking Information . . . . . . . . . . .  26
       3.7.3.  Updating Inventory Knowledge Based on Events  . . . .  27
       3.7.4.  Using Event Records in SW Attributes  . . . . . . . .  27
       3.7.5.  Partial and Complete Lists of Event Records in SW
               Attributes  . . . . . . . . . . . . . . . . . . . . .  28
       3.7.6.  Synchronizing Event Identifiers and Epochs  . . . . .  30
     3.8.  Subscriptions . . . . . . . . . . . . . . . . . . . . . .  31
       3.8.1.  Establishing Subscriptions  . . . . . . . . . . . . .  31
       3.8.2.  Managing Subscriptions  . . . . . . . . . . . . . . .  32



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       3.8.3.  Terminating Subscriptions . . . . . . . . . . . . . .  32
       3.8.4.  Subscription Status . . . . . . . . . . . . . . . . .  33
       3.8.5.  Fulfilling Subscriptions  . . . . . . . . . . . . . .  34
         3.8.5.1.  Subscriptions Reporting Inventories . . . . . . .  35
         3.8.5.2.  Subscriptions Reporting Events  . . . . . . . . .  35
         3.8.5.3.  Targeted Subscriptions  . . . . . . . . . . . . .  37
         3.8.5.4.  No Subscription Consolidation . . . . . . . . . .  37
         3.8.5.5.  Delayed Subscription Fulfillment  . . . . . . . .  37
     3.9.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  38
   4.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .  40
     4.1.  Direct Response to a SW Request . . . . . . . . . . . . .  40
     4.2.  Subscription-Based Response . . . . . . . . . . . . . . .  40
     4.3.  Required Exchanges  . . . . . . . . . . . . . . . . . . .  41
   5.  Software Inventory Messages and Attributes  . . . . . . . . .  41
     5.1.  PA Subtype (AKA PA-TNC Component Type)  . . . . . . . . .  42
     5.2.  SW Attribute Overview . . . . . . . . . . . . . . . . . .  42
     5.3.  Message Diagram Syntax  . . . . . . . . . . . . . . . . .  44
     5.4.  Software Inventory Message and Attributes for PA-TNC
           Attribute Enumeration . . . . . . . . . . . . . . . . . .  44
     5.5.  Normalization of Text Encoding  . . . . . . . . . . . . .  45
     5.6.  Request IDs . . . . . . . . . . . . . . . . . . . . . . .  46
     5.7.  SW Request  . . . . . . . . . . . . . . . . . . . . . . .  47
     5.8.  Software Identifier Inventory . . . . . . . . . . . . . .  50
     5.9.  Software Identifier Events  . . . . . . . . . . . . . . .  54
     5.10. Software Inventory  . . . . . . . . . . . . . . . . . . .  59
     5.11. Software Events . . . . . . . . . . . . . . . . . . . . .  62
     5.12. Subscription Status Request . . . . . . . . . . . . . . .  67
     5.13. Subscription Status Response  . . . . . . . . . . . . . .  67
     5.14. Source Metadata Request . . . . . . . . . . . . . . . . .  69
     5.15. Source Metadata Response  . . . . . . . . . . . . . . . .  69
     5.16. PA-TNC Error as Used by Software Inventory Message and
           Attributes for PA-TNC . . . . . . . . . . . . . . . . . .  71
       5.16.1.  SW_ERROR,           SW_SUBSCRIPTION_DENIED_ERROR and
                SW_SUBSCRIPTION_ID_REUSE_ERROR Information . . . . .  73
       5.16.2.  SW_RESPONSE_TOO_LARGE_ERROR Information  . . . . . .  75
       5.16.3.  SW_SUBSCRIPTION_FULFILLMENT_ERROR Information  . . .  76
   6.  Supported Data Models . . . . . . . . . . . . . . . . . . . .  78
     6.1.  ISO 2015 SWID Tags using XML  . . . . . . . . . . . . . .  78
       6.1.1.  Guidance on Normalizing Source Data to ISO 2015 SWID
               Tags using XML  . . . . . . . . . . . . . . . . . . .  79
       6.1.2.  Guidance on Creation of Software Identifiers from ISO
               2015 SWID Tags  . . . . . . . . . . . . . . . . . . .  79
     6.2.  ISO 2009 SWID Tags using XML  . . . . . . . . . . . . . .  79
       6.2.1.  Guidance on Normalizing Source Data to ISO 2009 SWID
               Tags using XML  . . . . . . . . . . . . . . . . . . .  80
       6.2.2.  Guidance on Creation of Software Identifiers from ISO
               2009 SWID Tags  . . . . . . . . . . . . . . . . . . .  80
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  80



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     7.1.  Evidentiary Value of Software Inventory Evidence Records   81
     7.2.  Sensitivity of Collected Records  . . . . . . . . . . . .  81
     7.3.  Integrity of Endpoint Records . . . . . . . . . . . . . .  82
     7.4.  SW-PC Access Permissions  . . . . . . . . . . . . . . . .  83
     7.5.  Sanitization of Record Fields . . . . . . . . . . . . . .  83
     7.6.  PA-TNC Security Threats . . . . . . . . . . . . . . . . .  83
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  84
   9.  Relationship to Other Specifications  . . . . . . . . . . . .  84
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  84
     10.1.  PA Subtypes  . . . . . . . . . . . . . . . . . . . . . .  85
     10.2.  Registry for PA-TNC Attribute Types  . . . . . . . . . .  85
     10.3.  Registry for PA-TNC Error Codes  . . . . . . . . . . . .  86
     10.4.  Registry for Software Data Models  . . . . . . . . . . .  87
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  88
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  88
     11.2.  Informative References . . . . . . . . . . . . . . . . .  89
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  90
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  90

1.  Introduction

   Knowing the list of the software installed on endpoints is useful to
   understand and maintain the security state of a network.  For
   example, if an enterprise policy requires the presence of certain
   software and prohibits the presence of other software, reported
   software installation information can be used to indicate compliance
   and non-compliance with these requirements.  When reported endpoint
   software installation inventory lists, shortened to "software
   inventories" for the remainder of this document, contain patch level
   data for identified software, further comparison to vulnerability or
   threat alerts can be used to determine an endpoint's exposure to
   attack.  These are some of the highly useful management use cases
   supported by software inventory data provided by this specification.

   There is a need for a standardized method for exchanging software
   inventory data that includes a unique software identifier associated
   with a specific version of a software product.  In some cases, it may
   also be necessary to convey observable installation information and
   characterization information for a software product including
   metadata about the product beyond its identifier.  These "Messages
   and Attributes" enable software identification, installation, and
   characterization information to be provided for any software
   installed on any endpoint that supports this specification.  Such
   information can come from multiple sources, including tag files (such
   as ISO SWID tags [SWID15]), reports from third party inventory tools,
   output from package managers, and other sources.





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   This specification is designed to only report software that is
   installed on an endpoint.  In particular, it does not monitor or
   report information about what software is running on the endpoint.
   Likewise, it is not intended to report individual files, libraries,
   installation packages, or similar artifacts.  While all of this
   information has its uses, this information requires different
   metadata and monitoring methods.  As a result, this specification
   focuses solely on software inventory information, leaving reporting
   of other classes of endpoint information to other specifications.

   This specification defines a new set of PA-TNC attributes, which are
   used to communicate requests for software inventory information and
   software installation change events.  The exchange of these messages
   allows software inventory information to be sent to a NEA Server,
   which can make this information available to other applications.

1.1.  Network Endpoint Assessment (NEA)

   The Network Endpoint Assessment (NEA) Working Group defines an open
   solution architecture that enables network operators to collect and
   utilize information about endpoint configuration and state.  This
   information can be used to enforce policies, monitor endpoint health,
   and for many other activities.  Information about the software
   present on an endpoint is an important consideration for such
   activities.  The attributes defined in this document are used to
   communicate software inventory evidence, collected from a range of
   possible sources, from the posture collector on the endpoint to the
   posture validator on a NEA Server using the PA-TNC interface, as
   shown in Figure 1 below.






















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       +-------------+                          +--------------+
       |  Posture    |   <--------PA-------->   |   Posture    |
       |  Collectors |                          |   Validators |
       |  (1 .. N)   |                          |   (1 .. N)   |
       +-------------+                          +--------------+
             |                                         |
             |                                         |
             |                                         |
       +-------------+                          +--------------+
       |   Posture   |                          |   Posture    |
       |   Broker    |   <--------PB-------->   |   Broker     |
       |   Client    |                          |   Server     |
       +-------------+                          +--------------+
             |                                         |
             |                                         |
       +-------------+                          +--------------+
       |   Posture   |                          |   Posture    |
       |   Transport |   <--------PT-------->   |   Transport  |
       |   Client    |                          |   Server     |
       |   (1 .. N)  |                          |   (1 .. N)   |
       +-------------+                          +--------------+
          NEA CLIENT                               NEA SERVER


                       Figure 1: NEA Reference Model

   To better understand this specification, the reader should review the
   NEA reference architecture as described in the Network Endpoint
   Assessment (NEA): Overview and Requirements [RFC5209].  The reader
   should also review the PA-TNC interfaces as defined in RFC 5792
   [RFC5792].

   This document is based on standards published by the Trusted
   Computing Group's Trusted Network Communications (TNC) workgroup.
   The TNC and NEA architectures are interoperable and the following
   components are equivalent:















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     +---------------------------------------+-----------------------+
     | TNC Component                         | NEA Component         |
     +---------------------------------------+-----------------------+
     | Integrity Measurement Verifier (IMV)  | Posture Validator     |
     |                                       |                       |
     | Integrity Measurement Collector (IMC) | Posture Collector     |
     |                                       |                       |
     | TNC Server (TNCS)                     | Posture Broker Server |
     |                                       |                       |
     | TNC Client (TNCC)                     | Posture Broker Client |
     +---------------------------------------+-----------------------+

        Table 1: Equivalent components in TNC and NEA architectures

1.2.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   specification are to be interpreted as described in RFC 2119
   [RFC2119].  This specification does not distinguish blocks of
   informative comments and normative requirements.  Therefore, for the
   sake of clarity, note that lower case instances of must, should, etc.
   do not indicate normative requirements.

1.3.  Definitions

   This section defines terms with special meaning within this document.

   SW-PC - A Posture Collector (PC) that conforms to this specification.
   Note that such a posture collector might also support other PA-TNC
   exchanges beyond those defined herein.

   SW-PV - A Posture Validator (PV) that conforms to this specification.
   Note that such a posture verifier might also support other PA-TNC
   exchanges beyond those defined herein.

   SW Attribute - This is a PA-TNC attribute (as defined in RFC 5792
   [RFC5792] extension for conveying software inventory information.
   This specification defines several new attribute types.

   Endpoint's Software Inventory Evidence Collection - The set of
   information regarding the set of software installed on an endpoint.
   An endpoint's software inventory evidence collection might include
   information created by or derived from multiple sources, including
   but not limited to SWID tag files deposited on the file system during
   software installation, information generated to report output from
   software discovery tools, and information dynamically generated by a
   software or package management system on an endpoint.



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   Software Inventory Evidence Record - The endpoint's Software
   Inventory Evidence Collection is composed of "records".  Each record
   corresponds to one installed instance of a particular software
   product as reported by some data source.  It is possible for a single
   installed instance to have multiple software inventory evidence
   records in an endpoint's Software Inventory Evidence Collection -
   this can happen if multiple sources all report the same software
   installation instance.

   Software Identifier - A string associated with a specific version of
   a specific software product.  Each supported SWIMA data model has its
   own rules for how a software identifier (see Section 3.4.1) is
   derived from the representation of the given software product using
   that data model, and different sources for this information might
   populate relevant information differently.  As such, while each
   software identifier uniquely identifies a specific software product,
   the same software product might be associated with multiple software
   identifiers reflecting differences between different data sources and
   supported data models.

2.  Background

2.1.  Supported Use Cases

   This section describes the use cases supported by this specification.
   The primary use of exchanging software inventory information over the
   PA-TNC interface is to enable a challenger (e.g.  NEA Server) to
   obtain inventory evidence about some system in a way that conforms to
   NEA procedures and expressed using a standard format.  Collected
   software information can support a range of security activities
   including determining whether an endpoint is permitted to connect to
   the enterprise, determining which endpoints contain software that
   requires patching, and similar activities.

2.1.1.  Use Software Inventory as an Access Control Factor

   Some enterprises might define security policies that require
   connected endpoints to have certain pieces of security software
   installed.  By contrast, some security policies might prevent access
   to resources by endpoints that have certain prohibited pieces of
   software installed, since such applications might pose a security
   risk.  To support such policies, the NEA Server needs to collect
   software inventory evidence from an endpoint that is seeking to
   initiate or continue connectivity to the enterprise resource.

   Based on this specification, the SW-PC can provide a complete or
   partial inventory to the SW-PV as required to determine policy




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   compliance.  The SW-PV can then use this as evidence of compliance or
   non-compliance to make a policy-based access decision.

2.1.2.  Central Stores of Up-to-Date Endpoint Software Inventory Data

   Many tools use information about an endpoint's software inventory to
   monitor and enforce the security of a network.  For example, a
   software patching tool needs to determine if there is out-of-date
   software installed that needs to be updated.  A vulnerability
   management tool needs to identify endpoints with known vulnerable
   software installed (patched or otherwise) to gauge an endpoint's
   relative exposure to attack.  A license management tool needs to
   verify that all installed software within the enterprise is accounted
   for.  A central repository representing an up-to-date understanding
   of each endpoint's software inventory facilitates these activities.
   Multiple tools can share such a repository ensuring that software
   inventory information is collected more frequently and efficiently,
   leading to a more complete and consistent understanding of installed
   software state as compared to each tool collecting the same inventory
   information from endpoints individually.

   This specification supports these activities through a number of
   mechanisms.  As noted above, a SW-PC can provide a complete list of
   software present in an endpoint's Software Inventory Evidence
   Collection to the SW-PV, which can then pass this information on to a
   central repository, such as a Configuration Management Database
   (CMDB) or similar application.  In addition, SW-PCs are required to
   be able to monitor for changes to an endpoint's Software Inventory
   Evidence Collection in near real-time and immediately push reports of
   detected changes to the SW-PV.  Thus any central repository fed by a
   SW-PV receiving inventory information can be updated quickly after a
   change occurs.  Keeping a central repository synchronized with
   current software inventory information in this way allows tools to
   make efficient decisions based on up-to-date, consistent information.

2.1.3.  PA-TNC Use Cases

   Software Inventory Message and Attributes for PA-TNC are intended to
   operate over the PA-TNC interface and, as such, are intended to meet
   the use cases set out in the PA-TNC specification.

2.2.  Non-supported Use Cases

   Some use cases not covered by this specification include:

   o  Addressing how the endpoint's Software Inventory Evidence
      Collection is populated.  In particular, NEA components are not
      expected to perform software discovery activities beyond compiling



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      information in an endpoint's Software Inventory Evidence
      Collection.  This collection might come from multiple sources on
      the endpoint (e.g., information generated dynamically by package
      management tools or discovery tools, as well as SWID tag files
      discovered on the file system).  While an enterprise might make
      use of software discovery capabilities to identify installed
      software, such capabilities are outside the scope of this
      specification.

   o  Converting inventory information expressed in a proprietary format
      into formats used in the attributes described in this
      specification.  Instead, this specification focuses exclusively on
      defining interfaces for the transportation of software information
      expecting that reporting tools will converge around some set of
      standardized formats for this information.

   o  Mechanisms for a posture validator to request a specific list of
      software information based on arbitrary software properties.  For
      example, requesting only information about software from a
      particular vendor is not supported.  After the endpoint's Software
      Inventory Evidence Collection has been copied to some central
      location, such as the CMDB, processes there can perform queries
      based on any criteria present in the collected information, but
      this specification does not address using such queries to
      constrain the initial collection of this information from the
      endpoint.

   o  Use of properties of certain sources of software information that
      might facilitate local tests (i.e., on the endpoint) of endpoint
      state.  For example, the optional package_footprint field of an
      ISO SWID tag can contain a list of files and hash values
      associated with the software indicated by the tag.  Tools on the
      endpoint can use the values in this field to test for the presence
      of the indicated files.  Successful evaluation of such tests leads
      to greater assurance that the indicated software is present on the
      endpoint.  Currently, most SWID tag creators do not provide values
      for tag fields that support local testing.  For this reason, the
      added complexity of supporting endpoint testing using these fields
      is out of scope for this specification, but may be considered in a
      future version.

2.3.  Specification Requirements

   Below are the requirements that the Software Inventory Message and
   Attributes for PA-TNC specification is required to meet in order to
   successfully play its role in the NEA architecture.





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   Efficient:  The NEA architecture enables delay of network access
      until the endpoint is determined not to pose a security threat to
      the network based on its asserted integrity information.  To
      minimize user frustration, the Software Inventory Message and
      Attributes for PA-TNC ought to minimize overhead delays and make
      PA-TNC communications as rapid and efficient as possible.

      Efficiency is also important when one considers that some network
      endpoints are small and low powered, some networks are low
      bandwidth and/or high latency, and some transport protocols (such
      as PT-EAP, Posture Transport (PT) Protocol for Extensible
      Authentication Protocol (EAP) Tunnel Methods [RFC7171]) or their
      underlying carrier protocol might allow only one packet in flight
      at a time or only one roundtrip.  However, when the underlying PT
      protocol imposes fewer constraints on communications, this
      protocol ought to be capable of taking advantage of more robust
      communication channels (e.g. using larger messages or multiple
      roundtrips).

   Scalable:  Software Inventory Message and Attributes for PA-TNC needs
      to be usable in enterprises that contain tens of thousands of
      endpoints or more.  As such, it needs to allow a security tools to
      make decisions based on up-to-date information about an endpoint's
      software inventory without creating an excessive burden on the
      enterprise's network.

   Interoperable:  This specification defines the protocol for how PCs
      and PVs can exchange and use software information to provide a NEA
      Server with information about an endpoint's software inventory.
      Therefore, a key goal for this specification is ensuring that all
      SW PCs and PVs, regardless of the vendor who created them, are
      able to interoperate in their performance of these duties.

   Support precise and complete historical reporting:  This
      specification outlines capabilities that support real-time
      understanding of the state of endpoint in a network in a way that
      can be used by other tools.  One means of facilitating such an
      outcome is for a CMDB to be able to contain information about all
      endpoints connected to the enterprise for all points in time
      between the endpoint's first connection and the present.  In such
      a scenario, it is necessary that any PC be able to report any
      changes to its software inventory evidence collection in near
      real-time while connected and, upon reconnection to the
      enterprise, be able to update the NEA Server (and through it the
      CMDB) with regard to the state of its software inventory evidence
      collection throughout the entire interval when it was not
      connected.




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2.4.  Non-Requirements

   There are certain requirements that the Software Inventory Message
   and Attributes for PA-TNC specification explicitly is not required to
   meet.  This list is not exhaustive.

   End to End Confidentiality:  This specification does not define a
      mechanism for confidentiality, nor is this property automatically
      provided by using the PA-TNC interface.  In the NEA architecture,
      confidentiality is generally provided by the underlying transport
      protocols, such as the PT Binding to TLS [RFC6876] or PT-EAP
      Posture Transport for Tunneled EAP Methods [RFC7171] - see
      Section 9 for more information on related standards.  Should users
      wish to protect the confidentiality of assessment instructions or
      results, then an appropriate transport needs to be used.

2.5.  Assumptions

   The Posture Broker Client and Posture Broker Server are assumed to
   provide reliable delivery for PA-TNC messages and attributes sent
   between the SW-PCs and the SW-PVs.  In the event that reliable
   delivery cannot be provided, the Posture Collector or Posture
   Validator is expected to terminate the connection.

2.6.  Non-Assumptions

   This specification explicitly does not assume that software inventory
   information exchanges reflect the software installation state of the
   endpoint.  This specification does not attempt to detect when the
   endpoint is providing false information, either through malice or
   error, but instead focuses on correctly and reliably providing the
   reported Software Inventory Evidence Collection to the NEA Server.
   Similarly, this specification makes no assumption about the
   completeness of the Software Inventory Evidence Collection's coverage
   of the total set of software installed on the endpoint.  It is
   possible, and even likely, that some installed software is not
   represented by a record in an endpoints Software Inventory Evidence
   Collection.  See Section 7 for more on this security consideration.

3.  System Requirements

   The Software Inventory Message and Attributes for PA-TNC
   specification facilitates the exchange of software inventory and
   event information.  Specifically, each application supporting
   Software Inventory Message and Attributes for PA-TNC includes a
   component known as the SW-PC that receives messages sent with the SW
   Attributes component type.  The SW-PC is also responsible for sending
   appropriate SW Attributes back to the SW-PV in response.  This



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   section outlines what software inventories and events are and the
   requirements on SW-PCs and SW-PVs in order to support the stated use
   cases of this specification.

3.1.  Data Sources

   The records in an endpoint's software inventory evidence collection
   come from one or more "sources".  A source represents one collection
   of software inventory information about the endpoint.  Examples of
   sources include, but are not limited to, ISO SWID tags deposited on
   the filesystem and collected therefrom, information derived from
   package managers (e.g., RPM or YUM), and the output of software
   inventory scanning tools.

   There is no expectation that any one source of inventory information
   will have either perfect or complete software inventory information.
   For this reason, this specification supports the simultaneous use of
   multiple sources of software inventory information.  Each source
   might have its own "sphere of expertise" and report the software
   within that sphere.  For example, a package manager would have
   excellent understanding of the software that it managed, but would
   not necessarily have any information about software installed via
   other means.

   A SW-PC is not required to utilize every possible source of software
   information on its endpoint.  Some SW-PCs might be explicitly tied
   only to one or a handful of software inventory sources, or it could
   be designed to dynamically accommodate new sources.  For all software
   inventory evidence sources that a particular SW-PC supports, it MUST
   completely support all requirements of this specification with regard
   to those sources.  A potential source that cannot support some set of
   required functionality (e.g. it is unable to monitor the software it
   reports for change events, as discussed in Section 3.6) MUST NOT be
   used as a source of endpoint software inventory information, even if
   it could provide some information.  In other words, a source either
   supports full functionality as described in this specification, or it
   cannot be used at all.

   When sending information about installed software the SW-PC MUST
   include the complete set of relevant data from all supported sources
   of software inventory evidence.  In other words, sources need to be
   used consistently.  This is because, if a particular source is
   included in an initial inventory, but excluded from a later
   inventory, the SW-PV receiving this information might reasonably
   conclude that the software reported by that source was no longer
   installed on the endpoint.  As such, it is important that all
   supported sources be used every time the SW-PC provides information
   to a SW-PV.



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   Note that, if a SW-PC collects data from multiple sources, it is
   possible that some software products might be "double counted".  This
   can happen if both sources of inventory evidence provide a record for
   a single installation of a software product.  When a SW-PC reports
   information or records events from multiple inventory evidence
   sources, it MUST use the information those sources provide, rather
   than attempting to perform some form of reduction.  In other words,
   if multiple sources report records corresponding to a single
   installation of a software product, all such records from each source
   are required to be part of the SW- PC's processing even if this might
   lead to multiple reporting, and the SW-PC is not to ignore some
   records to avoid such multiple reporting.

   All inventory records reported by a SW-PC include a Source Identifier
   linking them to a particular source.  Source Identifiers are
   discussed more in Section 3.4.5.

3.2.  Data Models

   Software Inventory Message and Attributes supports an open set of
   data models by which installed software instances can be described.
   This reflects the fact that, as of the writing of this specification,
   no one software description data model has come to dominate use, and
   new models are being developed regularly.  As a result, information
   available to SW-PCs might come in a variety of formats, and a SW-PC
   could have little control over the format of the data it is able to
   collect.

   The format of the data model used to convey software inventory
   information had very little impact on the behavior of the components
   defined in this specification.  The SW-PV has no dependency on the
   data model conveyed in SWIMA messages.  For this reason, it MUST NOT
   reject a record or respond with a PA-TNC Error due to the data model
   used in attributes it receives.  (Note that the SW-PV might serve as
   the front-end of other functionality that does have a dependency on
   the data model used to express software information, but any such
   dependency is beyond the scope of this specification and needs to be
   addressed outside the behaviors specified in this document.  This
   specification is only concerned with collection and delivery of
   software inventory information; components that consume and use this
   information are a separate concern.)

   The SW-PC does have one functional dependency on the data models used
   in the software records it delivers, but only insofar as it is
   required to deterministically create a Software Identifier (described
   in Section 3.4.1) based on each record it delivers.  The SW-PC MUST
   be able to generate a Software Identifier for each record it
   delivers, and if the SW-PC cannot do so the record cannot be



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   delivered by the SW-PC.  All SW-PCs MUST at least be able to generate
   Software Identifiers for the data model types specified in Section 6
   of this document.  A SW-PC MAY include the ability to generate
   Software Identifiers for other data model types, and thus be able to
   support them as well.

3.3.  Basic Attribute Exchange

   In the most basic exchange supported by this specification, a SW-PV
   sends a request to the SW-PC requesting some type of information
   about the endpoint's software inventory.  This simple exchange is
   shown in Figure 2.


       +-------------+                          +--------------+
       |   SW-PC     |                          |    SW-PV     |  Time
       +-------------+                          +--------------+   |
             |                                         |           |
             |<--------------SW Request----------------|           |
             |                                         |           |
             |---------------SW Response-------------->|           |
             |                                         |           V


                   Figure 2: Basic SW Attribute Exchange

   Upon receiving such a SW Request from the SW-PV, the SW-PC is
   expected to collect all the relevant software inventory information
   from the endpoint's software evidence collection and place it within
   its response attribute.

   SW-PVs MUST discard without error any SW Response attributes that
   they receive for which they do not know the SW Request parameters
   that led to this SW Response.  This is due to the fact that the SW
   Request includes parameters that control the nature of the response
   (as will be described in the following sections) and without knowing
   those parameters the SW Response cannot be reliably interpreted.
   Most often receiving an unsolicited SW Response attribute happens
   when a NEA Server has multiple SW-PVs; one SW-PV sends a SW Request
   but, unless exclusive delivery is used by the SW-PC in sending the
   response, both SW-PVs receive copies of the resulting SW Response.
   In this case, the SW-PV that didn't send the SW Request would lack
   the context necessary to correctly interpret the SW Response it
   received and would simply discard it.  Note, however, that
   proprietary measures might allow a SW-PV to discover the SW Request
   parameters for a SW Response even if that SW-PV did not send the
   given SW Request.  As such, there is no blanket requirement for a SW-
   PV to discard all SW Responses to SW Request the SW-PV did not



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   generate itself, only that SW-PVs are required to discard SW
   Responses for which they cannot get the necessary context to
   interpret.

   In the case that it is possible to do so, the SW-PC SHOULD send its
   SW Response attribute to the SW-PV that requested it using exclusive
   delivery as described in section 4.5 of RFC 5793 (PB-TNC) [RFC5793].
   Exclusive delivery ensures that only the sender of the SW Request
   receives the resulting SW Response.

3.4.  Core Software Reporting Information

   Different parameters in the SW Request can influence what information
   is returned in the SW Response.  However, while each SW Response
   provides different additional information about this installed
   software, they all share a common set of fields that support reliable
   software identification on an endpoint.  These fields include:
   Software Identifiers, the Data Model Type, Record Identifiers,
   Software Locators, and Source Identifiers.  These fields are present
   for each reported piece of software in each type of SW Response.  The
   following sections examine these three types of information in more
   detail.

3.4.1.  Software Identifiers

   A Software Identifier uniquely identifies a specific version of a
   specific software product.  The Software Inventory Message and
   Attributes for PA-TNC specification does not dictate the structure of
   a Software Identifier (beyond stating that it is a string) or define
   how it is created.  Instead, each data model described in the
   Software Data Model IANA table (Section 10.4) includes its own rules
   for how a Software Identifier is created based on a record in the
   Endpoint's Software Inventory Evidence Collection expressed in that
   data model.  Other data models will have their own procedures for the
   creation of associated Software Identifiers.  Within the Software
   Inventory Message and Attributes for PA-TNC specification, the
   Software Identifier is simply an opaque string and there is never any
   need to unpack any information that might be part of that identifier.

   A Software Identifier is a fraction of the size of the inventory
   record from which it is derived.  For some combinations of data
   models and sources, the full record might never be necessary as the
   identifier can be directly correlated to the contents of the full
   record.  This is possible with authoritative SWID tags, since these
   tags always have the same contents and thus a Software Identifier
   derived from these tags can be used as a lookup to a local copy of
   the full tag.  For other combinations of source and data model, a
   server might not be able to determine the specific software product



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   and version associated with the identifier without requesting
   delivery of the full record.  However, even in those cases,
   downstream consumers of this information might never need the full
   record as long as the Software Identifiers they receive can be
   tracked reliably.  A SW-PV can use Software Identifiers to track the
   presence of specific software products on an endpoint over time in a
   bandwidth-efficient manner.

   There are two important limitations of Software Identifiers to keep
   in mind:

   1.  The identifiers do not necessarily change when the associated
       record changes.  In some situations, a record in the endpoint's
       Software Inventory Evidence Collection will change due to new
       information becoming available or in order to correct prior
       errors in that information.  Such changes might or might not
       result in changes to the Software Identifier, depending on the
       nature of the changes and the rules governing how Software
       Identifiers are derived from records of the appropriate data
       model.

   2.  It is possible that a single software product is installed on a
       single endpoint multiple times.  If both of these installation
       instances are reported by the same source using the same data
       format, then this can result in identical Software Identifiers
       for each installation instances.  In other words, Software
       Identifiers might not uniquely identify installation instances;
       they just are intended to uniquely identify software products
       (which might have more than one installation instance).  Instead,
       to reliably distinguish between multiple instances of a single
       software product, one needs to make use of Record Identifiers,
       described in the following section.

3.4.2.  Data Model Type

   The Data Model Type consists of two fields: the Data Model Type PEN
   and the Data Model Type.  The combination of these fields is used to
   identify the type of data model of the associated software inventory
   record.  The data model is significant not only because it informs
   the recipient of the data model of the associated record, but because
   the Software Identifier of the record is derived directly from the
   data recorded in that data model.  As a result, Software Identifiers
   for the same software product but expressed via different data models
   might be different.  Clearly identifying the type of data model from
   with the Software Identifier was derived thus provides useful context
   for that value.





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   The PEN (or Private Enterprise Number) identifies the organization
   that assigns meaning to the Data Model Type field value.  PENs are
   managed by IANA in the Private Enterprise Numbers registry.  PENs
   allow vendors to designate their own set of data models for software
   inventory description.  IANA reserves the PEN of 0x000000.  Data
   Model Types associated with this PEN are defined in the Software Data
   Model IANA table, created in Section 10.4 of this specification.
   Note that this IANA table reserves all values greater than or equal
   to 0xC0 (192) for enterprise use.  This means that local enterprises
   can use custom data formats and indicate them with the IANA PEN and a
   Data Model Type value between 0xC0 and 0XFF, inclusive.  Those
   enterprises are responsible for configuring their SW-PCs to correctly
   report those custom data models.

3.4.3.  Record Identifiers

   A Record Identifier is a 4-byte integer generated by the SW-PC that
   is uniquely associated with a specific record within the Endpoint's
   Software Inventory Evidence Collection.  The SW-PC MUST assign a
   unique identifier to each record when it is added to the Endpoint's
   Software Inventory Evidence Collection.  The Record Identifier SHOULD
   remain unchanged if that record is modified.  The SWID-PC might wish
   to assign Record Identifiers sequentially, but any scheme is
   acceptable provided that no two records receive the same identifier.

   Servers can use Record Identifiers to distinguish between multiple
   instances of a single software product installed on an endpoint.
   Since each installation instance of a software product is associated
   with a separate record, servers can use the record identifier to
   distinguish between instances.  For example, if an event is reported
   (as described in Section 3.7), the record identifier will allow the
   server to discern which instance of a software product is involved.

3.4.4.  Software Locators

   In addition to the need to identify software products, many use cases
   of inventory information need to know where software is located on
   the endpoint.  This information might be needed to direct remediation
   actions or similar processes.  For this reason, every reported
   software product also includes a Software Locator to identify where
   the software is installed on the endpoint.

   If the location is not provided directly by the record source the SW-
   PC is responsible for attempting to determine the location of the
   software product.  The "location" of a product SHOULD be the
   directory in which the software products executables are kept.
   However, if that directory is shared by other software products, the
   "location" SHOULD be the location of the primary executable



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   associated with the software product.  The source and/or SW-PC MUST
   be consistent in reporting the location of a software product (i.e.,
   it cannot use the executable location in one report and the directory
   location in another).

   The location is expressed as a URI string consisting of a scheme and
   path.  [RFC3986] The location URI does not include an authority part.
   The URI schema describes the context of the described location.  For
   example, in most cases the location of the installed software product
   will be expressed in terms of its path in the filesystem.  For such
   locations, the location URI scheme MUST be "file".  It is possible
   that other schemes could be used to represent other location
   contexts.  Apart from reserving the "file" and "unknown" (described
   below) scheme to indicate an installation location expressed using a
   path in the endpoint's file system, this specification does not
   reserve schemes.  When representing software products in other
   location contexts, tools MUST be consistent in their use of schemes,
   but the exact string used in those schemes is not normatively defined
   here.

   It is possible, that a SW-PC is unable to determine the location of a
   reported software product.  In this case, the SW-PC MUST assign that
   software product a location of "unknown:".  (I.e., the "unknown"
   scheme and an empty path.)  However, SW-PCs SHOULD only make such an
   assignment as a last resort.  Even a probable location for a software
   product is preferable to using the unknown indicator.

3.4.5.  Source Identifiers

   All SW-PCs MUST track the source of each piece of software
   information they report.  Each time a SW-PC gets information to send
   to a given SW-PV from a new source (from the perspective of that SW-
   PV), the SW-PC MUST assign that source a Source Identification
   Number, which is an 8-bit unsigned integer.  Each item reported
   includes the Source Identification Number that provided that
   information.  All information that is provided by that source, MUST
   be delivered with this same Source Identification Number.  This MUST
   be done for each source used.  If the SW-PC ever is unclear as to
   whether a given source is new or not, it MUST assume that this is a
   new source and assign it a new Source Identification Number.  Source
   Identification Numbers can help with (although will not completely
   eliminate) the challenges posed by multiple reporting of a single
   software instance: since a single source would only report an
   instance or event once, if multiple reports of a similar instance
   come from multiple sources, this might be an instance of multiple
   reporting (although it still might not be so).  On the other hand, if
   multiple instances are reported by a single source, this almost




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   certainly means that there are actually multiple instance that are
   being legitimately reported.

   The SW-PC is responsible for tracking associations between Source
   Identifiers and the given data source.  This association MUST remain
   consistent with regard to a given SW-PV while there is an active PB-
   TNC session with that SW-PV.  The SW-PC MAY have a different Source
   Identifier association for different SW-PVs.  Likewise, the SW-PC MAY
   change the Source Identifier association for a given SW-PV if the PB-
   TNC session terminates.  However, implementers of SW-PCs will
   probably find it easier to manage associations by maintaining the
   same association for all SW-PVs and across multiple sessions.

   Of special note, events records reported from the SW-PC's event log
   (discussed in Section 3.7) also need to be sent with their associated
   data source.  The Source Identifier reported with events MUST be the
   current (i.e., at the time the event is sent) Source Identifier
   associated with the data source that produced the event, regardless
   of how long ago that event occurred.  Event logs are likely to
   persist far longer than a single PB-TNC session.  SW-PCs MUST ensure
   that each event can be linked to the appropriate data source, even if
   the Source Identifiers used when the event was created have since
   been reassigned.  In other words, when sending an event, it needs to
   be sent with the Source Identifier currently linked to the data
   source that produced it, regardless of whether a different Source
   Identifier would have been associated with the event when the event
   was first created.

   Note that the Source Identification Number is primarily used to
   support recognition, rather than identification, of sources.  That is
   to say, a Software Identification Number can tell a recipient that
   two events were reported by the same source, but will not necessarily
   help that recipient determine which source was used.  Moreover,
   different SW-PCs will not necessarily use the same Source
   Identification Numbers for the same sources.  SW-PCs MUST track the
   assignment of Source Identification Numbers to ensure consistent
   application thereof.  SW-PCs MUST also track which Source
   Identification Numbers have been used with each SW-PV with which they
   communicate.

3.4.6.  Using Software and Record Identifiers in SW Attributes

   A SW Attribute reporting an endpoint's Software Inventory Evidence
   Collection always contains the Software Identifiers associated with
   the identified software products.  A SW Attribute might or might not
   also contain copies of software inventory evidence records.  The
   attribute exchange is identical to the diagram shown in Figure 2
   regardless of whether software inventory evidence records are



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   included.  The SW Request attribute indicates whether the response is
   required to include software inventory evidence records.  Excluding
   software inventory evidence records can reduce the attribute size of
   the response by multiple orders of magnitude when compared to sending
   the same inventory with full records.

3.5.  Targeted Requests

   Sometimes a SW-PV does not require information about every piece of
   software on an endpoint but only needs to receive updates about
   certain software instances.  For example, enterprise endpoints might
   be required to have certain software products installed and to keep
   these updated.  Instead of requesting a complete inventory just to
   see if these products are present, the SW-PV can make a "targeted
   request" for the software in question.

   Targeted requests follow the same attribute exchange described in
   Figure 2.  The SW-PV targets its request by providing one or more
   Software Identifiers in its SW Request attribute.  The SW-PC MUST
   then limit its response to contain only records that match the
   indicated Software Identifier(s).  This allows the network exchange
   to exclude information that is not relevant to a given policy
   question, thus reducing unnecessary bandwidth consumption.  The SW-
   PC's response might or might not include software inventory evidence
   records, depending on the parameters of the SW Request.

   Note that targeted requests identify the software relevant to the
   request only through Software Identifiers.  This specification does
   not support arbitrary, parameterized querying of records.  For
   example, one cannot request all records from a certain software
   publisher, or all records created by a particular record source.
   Targeted requests only allow a requestor to request specific software
   (as identified by their Software Identifiers) and receive a response
   that is limited to the named software.

   There is no assumption that a SW-PC will recognize "synonymous
   records" - that is, records from different sources for the same
   software.  Recall that different sources and data models may use
   different Software Identifier strings for the same software product.
   The SW-PC returns only records that match the Software Identifiers in
   the SW Request, even if there might be other records in the
   endpoint's Software Inventory Evidence Collection for the same
   software product.  This is necessary because SW-PCs might not have
   the ability to determine that two Software Identifiers refer to the
   same product.

   Targeted requests do not include Record Identifiers or Software
   Locators.  The response to a targeted request MUST include all



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   records associated with the named Software Identifiers, including the
   case where there are multiple records associated with a single
   Software Identifier.

   SW-PCs MUST accept targeted requests and process them correctly as
   described above.  SW-PVs MUST be capable of making targeted requests
   and processing the responses thereto.

3.6.  Monitoring Changes in an Endpoint's Software Inventory Evidence
      Collection

   The software collection on an endpoint is not static.  As software is
   installed, uninstalled, patched, or updated, the Software Inventory
   Evidence Collection is expected to change to reflect the new software
   state on the endpoint.  Different record sources might update the
   evidence collection at different rates.  For example, a package
   manager might update its records in the Software Inventory Evidence
   Collection immediately whenever it is used to add or remove a
   software product.  By contrast, sources that perform periodic
   examination of the endpoint would likely only update their records in
   the Software Inventory Evidence Collection after each examination.

   All SW-PCs MUST be able to be able to detect changes to the Software
   Inventory Evidence Collection.  Specifically, SW-PCs MUST be able to
   detect:

   o  The creation of records

   o  The deletion of records

   o  The alteration of records

   An "alteration" is anything that modifies the contents of a record
   (or would modify it, if the record is dynamically generated on
   demand) in any way, regardless of whether the change is functionally
   meaningful.

   SW-PCs MUST detect such changes to the endpoint's Software Inventory
   Evidence Collection in close to real-time (i.e., within seconds) when
   the Posture Collector is operating.  In addition, in the case where
   there is a period during which the SW-PC is not operating, the SW-PC
   MUST be able to determine the net change to the endpoint's Software
   Inventory Evidence Collection over the period it was not operational.
   Specifically, the "net change" represents the difference between the
   state of the endpoint's Software Inventory Evidence Collection when
   the SW-PC was last operational and monitoring its state, and the
   state of the endpoint's software inventory evidence collection when
   the SW-PC resumed operation.  Note that a net change might not



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   reflect the total number of change events over this interval.  For
   example, if a record was altered three times during a period when the
   SW-PC was unable to monitor for changes, the net change of this
   interval might only note that there was an alteration to the record,
   but not how many individual alteration events occurred.  It is
   sufficient for a SW-PC's determination of a net change to note that
   there was a difference between the earlier and current state rather
   than enumerating all the individual events that allowed the current
   state to be reached.

   The SW-PC MUST assign a time to each detected change in the
   endpoint's Software Inventory Evidence Collection.  These timestamps
   correspond to the SW-PC's best understanding as to when the detected
   change occurred.  These timestamps MUST be as accurate as possible.
   For changes to the endpoint's Software Inventory Evidence Collection
   that occur while the SW-PC is operating, the SW-PC ought to be able
   to assign a time to the event that is accurate to within a few
   seconds.  For changes to the endpoint's Software Inventory Evidence
   Collection that occur while the SW-PC is not operational, upon
   becoming operational the SW-PC needs to make a best guess as to the
   time of the relevant events (possibly by looking at timestamps on
   files), but these values might be off.  In the case of dynamically
   generated records, the time of change is the time at which the data
   from which the records are generate changes, not the time at which a
   changed record is generated.  For example, if records are dynamically
   generated based on data in an RPM database, the time of change would
   be when the RPM database changed.

   With regard to deletions of records, the SW-PC needs to detect the
   deletion and MUST retain a copy of the full deleted record along with
   the associated Record Identifier and Software Locator so that the
   record and associated information can be provided to the SW-PV upon
   request.  This copy of the record MUST be retained for a reasonable
   amount of time.  Vendors and administrators determine what
   "reasonable" means, but a copy of the record SHOULD be retained for
   as long as the event recording the deletion of the record remains in
   the SW-PC's event log (as described in Section 3.7).  This is
   recommended because, as long as the event is in the SW-PC's change
   logs, the SW-PC might send an event attribute (described in
   Section 3.7) that references this record, and a copy of the record is
   needed if the SW-PV wanted a full copy of the relevant records.

   With regard to alterations to a record, SW-PCs MUST detect any
   alterations to the contents of a record.  Alterations need to be
   detected even if they have no functional impact on the record.  A
   good guideline is that any alteration to a record that might change
   the value of a hash taken on the record's contents needs to be
   detected by the SW-PC.  A SW-PC might be unable to distinguish



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   modifications to the content of a record from modifications to the
   metadata the file system associates with the record.  For example, a
   SW-PC might use the "last modification" timestamp as an indication of
   alteration to a given record, but a record's last modification time
   can change for reasons other than modifications to the record
   contents.  A SW-PC is still considered compliant with this
   specification if it also reports metadata change events that do not
   change the record itself as alterations to the record.  In other
   words, while SW-PC authors are encouraged to exclude modifications
   that do not affect the bytes within the record, discriminating
   between modifications to file contents and changes to file metadata
   can be difficult and time consuming on some systems.  As such, as
   long as the alterations detected by a SW-PC always cover all
   modifications to the contents of record, the SW-PC is considered
   compliant even if it also registers alterations that do not modify
   the contents of a record as well.  When recording an alteration to a
   record, the SW-PC is only required to note that an alteration
   occurred.  The SW-PC is not required to note or record how the record
   altered, nor is it possible to include such details in SW Attributes
   reporting the change to a SW-PV.  There is no need to retain a copy
   of the original record.

   When a record changes it SHOULD retain the same Record Identifier.
   The Software Locator might or might not change, depending on whether
   the software changed locations during the changes that led to the
   record change.  A record change MUST retain the same Software
   Identifier.  This means that any action that changes a software
   product (e.g., application of a patch that results in a change to the
   product's version) MUST NOT be reflected by a record change but
   instead MUST result in the deletion of the old record and the
   creation of a new record.  This reflects the requirement that a
   record in the endpoint's Software Inventory Evidence Collection
   correspond directly with an instance of a specific software product.

3.7.  Reporting Change Events

   As noted in the preceding section, SW-PCs MUST be able to detect
   changes to the endpoints Software Inventory Evidence Collection
   (creation, deletion, and alteration) in near real-time while the SW-
   PC is operational, and MUST be able to account for any net change to
   the endpoint's Software Inventory Evidence Collection that occurs
   when the SW-PC is not operational.  However, to be of use to the
   enterprise, the NEA Server needs to be able to receive these events
   and be able to understand how new changes relate to earlier changes.
   In Software Inventory Message and Attributes for PA-TNC, this is
   facilitated by reporting change events.  All SW-PCs MUST be capable
   of receiving requests for change events and sending change event




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   attributes.  All SW-PVs MUST be capable of requesting and receiving
   change event attributes.

3.7.1.  Event Identifiers

   To be useful, change events need to be correctly ordered.  Ordering
   of events is facilitated by two pieces of information: an Event
   Identifier (EID) value and an EID Epoch value.

   An EID is a 4-byte unsigned integer that the SW-PC assigns
   sequentially to each observed event (whether detected in real-time or
   deduced by looking for net changes over a period of SW-PC
   inactivity).  All EIDs exist within the context of some "EID Epoch",
   which is also represented as a 4-byte unsigned integer.  EID Epochs
   are used to ensure synchronization between the SW-PC and any SW-PVs
   with which it communicates.  EID Epoch values SHOULD be generated
   randomly and in such a way that it is unlikely that the same EID
   Epoch is generated twice, even if the SW-PC reverted to an earlier
   state (e.g., resetting it to factory defaults).  In the case where a
   SW-PC needs to reset its EID counter, either because it has exhausted
   all available EID values or because the SW-PC's event log becomes
   corrupted, then a new EID Epoch MUST be selected.

   Within an Epoch, EIDs MUST be assigned sequentially, so that if a
   particular event is assigned an EID of N, the next observed event is
   given an EID of N+1.  In some cases, events might occur
   simultaneously, or the SW-PC might not otherwise be able to determine
   an ordering for events.  In these cases, the SW-PC creates an
   arbitrary ordering of the events and assigns EIDs according to this
   ordering.  Two change events MUST NOT ever be assigned the same EID
   within the same EID Epoch.  No meaningful comparison can be made
   between EID values of different Epochs.

   The EID value of 0 is reserved and MUST NOT be associated with any
   event.  Specifically, an EID of 0 in a SW Request attribute indicates
   that a SW-PV wants an inventory response rather than an event
   response, while an EID of 0 in a SW Response is used to indicate the
   initial state of the endpoint's Software Inventory Evidence
   Collection prior to the observation of any events.  Thus the very
   first recorded event in a SW-PC's records within an EID Epoch MUST be
   assigned a value of 1 or greater.  Note that EID and EID Epoch values
   are assigned by the SW-PC without regard to whether events are being
   reported to one or more SW-PVs.  The SW-PC records events and assigns
   EIDs during its operation.  Any and all SW-PVs that request event
   information from the SW-PC will have those requests served from the
   same event records and thus will see the same EIDs and EID Epochs for
   the same events.




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   If a SW-PC uses multiple sources, a SW-PC's assignment of EIDs MUST
   reflect the presence and order of all events on the endpoint (at
   least for supported sources) regardless of the source.  This means
   that if source A experiences an event, and then source B experiences
   two events, and then source A experiences another two events, the SW-
   PC is required to capture five events with consecutive EID values
   reflecting the order in which the events occur.

   The SW-PC MUST ensure there is no coverage gap (i.e., change events
   that are not recorded in the SW-PC's records) in its change event
   records.  This is necessary because a coverage gap might give a SW-PV
   a false impression of the endpoint's state.  For example, if a SW-PV
   saw an event indicating that a particular record had been added to
   the endpoint's software inventory evidence collection, and saw no
   subsequent events indicating that record had been deleted, it might
   reasonably assume that this record was still present and thus that
   the indicated software was still installed (assuming the Epoch has
   not changed).  If there is a coverage gap in the SW-PC's event
   records, however, this assumption could be false.  For this reason,
   the SW-PC's event records MUST NOT contain gaps.  In the case where
   there are periods where it is possible that changes occurred without
   the SW-PC detecting or recording them, the SW-PC MUST either compute
   a net change and update its event records appropriately, or pick a
   new EID Epoch to indicate a discontinuity with previous event
   records.

   Within a given Epoch, once a particular event has been assigned an
   EID, this association MUST NOT be changed.  That is, within an Epoch,
   once an EID is assigned to an event, that EID cannot be reassigned to
   a different event, and the event cannot be assigned a different EID.
   When the SW-PC's Epoch changes, all of these associations between
   EIDs and events are cancelled, and EID values once again become free
   for assignment.

3.7.2.  Core Event Tracking Information

   Whether reporting events or full inventories it is important to know
   how the reported information fits into the overall timeline of change
   events.  This is why all SW Response attributes include fields to
   place that response within the sequence of detected events.
   Specifically, all SW Responses include a Last EID and EID Epoch
   field.  The EID Epoch field identifies the EID Epoch in which the SW
   Response was sent.  If the SW Response is reporting events, all
   reported events occurred within the named EID Epoch.  The Last EID
   (which is also always from the named EID Epoch) indicates the EID of
   the last recorded change event at the time that the SW Response was
   sent.  These two fields allow any response to be placed in the




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   context of the complete set of detected change events within a given
   EID Epoch.

3.7.3.  Updating Inventory Knowledge Based on Events

   Modern endpoints can have hundreds of software products installed,
   most of which are unlikely to change from one day to the next.  As
   such, instead of exchanging a complete list of an endpoint's
   inventory on a regular basis, one might wish to only identify changes
   since some earlier known state of this inventory.  This is readily
   facilitated by the use of EIDs to place change events in a context
   relative to earlier state.

   As noted above, every SW Response sent by a SW-PC to a SW-PV (as
   described in Section 3.3 through Section 3.5) includes the EID Epoch
   and EID of the last event recorded prior to that response being
   compiled.  This allows the SW-PV to place all subsequently received
   event records in context relative to this SW Response attribute
   (since the EIDs represent a total ordering of all changes to the
   endpoint's software inventory evidence collection).  Specifically, a
   SW-PV (or, more likely, a database that collects and records its
   findings) can record an endpoint's full inventory and also the EID
   and Epoch of the most recent event reflected at the time of that
   inventory.  From that point on, if change events are observed, the
   attribute describing these events indicates the nature of the change,
   the affected records, and the order in which these events occurred
   (as indicated by the sequential EIDs).  Using this information, any
   remote record of the endpoint's Software Inventory Evidence
   Collection can be updated appropriately.

3.7.4.  Using Event Records in SW Attributes

   A SW-PV MUST be able to request a list of event records instead of an
   inventory.  The attribute flow in such an exchange looks the same as
   the basic flow shown in Figure 2.  The only difference is that, in
   the SW Request attribute, the SW-PV provides an EID other than 0.  (A
   value of 0 in these fields represents a request for an inventory.)
   When the SW-PC receives such a request, instead of identifying
   records from the endpoint's Software Inventory Evidence Collection,
   it consults its list of detected changes.  The SW-PC MUST add an
   event record to the SW Response attribute for each recorded change
   event with an EID greater than or equal to the EID in the SW Request
   attribute (although targeting of requests, as described in the next
   paragraph, might limit this list).  A list of event records MUST only
   contain events with EIDs that all come from the current Epoch.

   SW-PVs can target requests for event records by including one or more
   Software Identifiers, as described in Section 3.5, in the SW Request



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   that requests an event record list.  A targeted request for event
   records is used to indicate that only events affecting software that
   matches one of the provided Software Identifiers are to be returned.
   Specifically, in response to a targeted request for event records,
   the SW-PC MUST exclude any event records that are less than the
   indicated EID (within the current EID Epoch) and exclude any event
   records where the affected software does not match one of the
   provided Software Identifiers.  This might mean that the resulting
   list of event records sent in the response attribute does not provide
   a continuous sequence of EIDs.  Both SW-PCs and SWIC-PVs MUST support
   targeted request for event records.

3.7.5.  Partial and Complete Lists of Event Records in SW Attributes

   Over time, a SW-PC might record a large number of change events.  If
   a SW-PV requests all change events covering a large period of time,
   the resulting SW Response attribute might be extremely large,
   especially if the SW-PV requests inclusion of software inventory
   evidence records in the response.  In the case that the resulting
   attribute is too large to send (either because it exceeds the 4GB
   attribute size limit imposed by the PA-TNC specification, or because
   it exceeds some smaller size limit imposed on the SW-PC) the SW-PC
   MAY send a partial list of event records back to the SW-PV.

   Generation of a partial list of events in a SW Response attribute
   requires the SW-PC to identify a "consulted range" of EIDs.  A
   consulted range is the set of event records that are examined for
   inclusion in the SW Response attribute and that are included in that
   attribute if applicable.  Recall that, if a SW Request is targeted,
   only event records that involve the indicated software would be
   applicable.  (See Section 3.5 for more on Targeted Request.)  If a
   request is not targeted, all event records in the considered range
   are applicable and included in the SW Response attribute.

   The lower bound of the consulted range MUST be the EID provided in
   the SW Request.  (Recall that a SW Request indicates a request for
   event records by providing a non-0 EID value in the SW Request.  See
   Section 3.7.4.)  The upper bound of the consulted range is the EID of
   the latest event record (as ordered by EID values) that is included
   in the SW Response attribute if it is applicable to the request.  The
   EID of this last event record is called the "Last Consulted EID".
   The SW-PC chooses this Last Consulted EID based on the size of the
   event record list it is willing to provide to the SW-PV.

   A partial result list MUST include all applicable event records
   within the consulted range.  This means that for any applicable event
   record (i.e., any event record in an un-targeted request, or any
   event record associated with software matching a requested Software



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   Identifier in a targeted request) whose EID is greater than or equal
   to the EID provided in the SW Request and whose EID is less than or
   equal to the Last Consulted EID, that event record MUST be included
   in the SW Response conveying this partial list of event records.
   This ensures that every partial list of event records is always
   complete within its indicated range.

   All SW Response attributes that convey event records include a Last
   Consulted EID field.  This is in addition to the EID Epoch and Last
   EID fields that are present in all SW Responses.  Note that, if
   responding to a targeted SW Request, the SW Response attribute might
   not contain the event record whose EID matches the Last Consulted EID
   value.  For example, the last consulted EID record might have been
   deemed inapplicable because it did not match the specified list of
   Software Identifiers in the SW Request.

   If a SW-PV receives a SW Response attribute where the Last EID and
   Last Consulted EID fields are identical, the SW-PV knows that it has
   received a result list that is complete, given the parameters of the
   request, up to the present time.

   On the other hand, if the Last EID is greater than the Last Consulted
   EID, the SW-PV has received a partial result list.  (The Last
   Consulted EID MUST NOT exceed the Last EID.)  In this case, if the
   SW-PV wishes to try to collect the rest of the partially delivered
   result list it then sends a new SW Request whose EID is one greater
   than the Last Consulted EID in the preceding response.  Doing this
   causes the SW-PC to generate another SW Response attribute containing
   event records where the earliest reported event record is the one
   immediately after the event record with the Last Consulted EID (since
   EIDs are assigned sequentially).  By repeating this process until it
   receives a SW Response where the Last EID and Last Consulted EID are
   equal, the SW-PV is able to collect all event records over a given
   range, even if the complete set of event records would be too large
   to deliver via a single attribute.

   Implementers need to be aware that a SW Request might specify an EID
   that is greater than the EID of the last event recorded by a SW-PC.
   In accordance with the behaviors described in Section 3.7.4, a SW-PC
   MUST respond to such a request with a SW Response attribute that
   contains zero event records.  This is because the SW-PC has recorded
   no event records with EIDs greater than or equal to the EID in the SW
   Request.  In such a case, the Last Consulted EID field MUST be set to
   the same value as the Last EID field in this SW Response attribute.
   This case is called out because the consulted range on a SW-PC in
   such a situation is a negative range, where the "first" EID in the
   range (provided in the SW Request) is greater than the "last" EID in
   the range (this being the EID of the last recorded event on the SW-



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   PC).  Implementers need to ensure that SW-PCs do not experience
   problems in such a circumstance.

   Note that this specification only supports the returning of partial
   results when returning event records.  There is no way to return a
   partial inventory list under this specification.

3.7.6.  Synchronizing Event Identifiers and Epochs

   Since EIDs are sequential within an Epoch, if a SW-PV's list of event
   records contains gaps in the EID values within a single Epoch, the
   SW-PV knows that there are events that have not been accounted for.
   The SW-PV can either request a new event list to collect the missing
   events or request a full inventory to re-sync its understanding of
   the state of the endpoint's Software Inventory Evidence Collection.
   In either case, after the SW-PV's record of the endpoint's Software
   Inventory Evidence Collection has been updated, the SW-PV can record
   the new latest EID value and track events normally from that point
   on.

   If the SW-PV receives any attribute from a SW-PC where the EID Epoch
   differs from the EID Epoch that was used previously, then SW-PV or
   any entity using this information to track the endpoint's Software
   Inventory Evidence Collection knows that there is a discontinuity in
   their understanding of the endpoint's state.  To move past this
   discontinuity and reestablish a current understanding of the state of
   the endpoint's Software Inventory Evidence Collection, the SW-PV
   needs to receive a full inventory from the endpoint.  The SW-PV
   cannot be brought in sync with the endpoint's state through the
   collection of any set of event records in this situation.  This is
   because it is not possible to account for all events on the SW-PC
   since the previous Epoch was used, because there is no way to query
   for EIDs from a previous Epoch.  Once the SW-PV has received a full
   inventory for the new Epoch, the SW-PV records the latest EID
   reported in this new Epoch and can track further events normally.

   A SW-PC MUST NOT report events with EIDs from any Epoch other than
   the current EID Epoch.  The SW-PC MAY choose to purge all event
   records from a previous Epoch from memory after an Epoch change.
   Alternately, the SW-PC MAY choose to retain some event records from a
   previous EID Epoch and assign them new EIDs in the current Epoch.
   However, in the case where a SW-PC chooses the latter option it MUST
   ensure that the order of events according to their EIDs is unchanged
   and that there is no coverage gap between the first retained event
   recorded during the previous Epoch (now reassigned with an EID in the
   current Epoch) and the first event recorded during the current Epoch.
   In particular, the SW-PC MUST ensure that all change events that
   occurred after the last recorded event from the previous Epoch are



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   known and recorded.  (This might not be possible if the Epoch change
   is due to state corruption on the SW-PC.)  A SW-PC might choose to
   reassign EIDs to records from a preceding Epoch to create a "sliding
   window" of events, where each Epoch change represents a shift in the
   window of available events.

   In the case where a SW-PC suffers a crash and loses track of its
   current EID Epoch or current EID, then it MUST generate a new EID
   Epoch value and begin assigning EIDs within that Epoch.  In this
   case, the SW-PC MUST purge all event records from before the crash as
   it cannot ensure that there is not a gap between the last of those
   records and the next detected event.  The process for generating a
   new EID Epoch MUST minimize the possibility that the newly generated
   EID Epoch is the same as a previously used EID Epoch.

   The SW-PV will normally never receive an attribute indicating that
   the latest EID is less than the latest EID reported in a previous
   attribute within the same EID Epoch.  If this occurs, the SW-PC has
   suffered an error of some kind, possibly indicative of at least
   partial corruption of its event log.  In this case, the SW-PV SHOULD
   treat the situation as if there was a change in Epoch and treat any
   local copy of the endpoint's Software Inventory Evidence Collection
   as out-of-sync until a full inventory can be reported by the SW-PC.
   In this case, the SW-PV SHOULD flag the occurrence so the SW-PC can
   be examined to ensure it is now operating properly.

3.8.  Subscriptions

   Thus far, all attribute exchanges discussed assume that a SW-PV sent
   an SW Request attribute and the SW-PC is providing a direct response
   to that request.  The Software Inventory Message and Attributes for
   PA-TNC specification also supports the ability for a SW-PC to send a
   SW Response to the SW-PV in response to observed changes in the
   endpoint's software inventory evidence collection, instead of in
   direct response to a SW Request.  An agreement by a SW-PC to send
   content when certain changes are detected to the endpoint's Software
   Inventory Evidence Collection is referred to in this specification as
   a "subscription", and the SW-PV that receives this content is said to
   be "subscribed to" the given SW-PC.  All SW-PCs and SW-PVs MUST
   support the use of subscriptions.

3.8.1.  Establishing Subscriptions

   A SW-PV establishes a subscription on a particular SW-PC by sending a
   SW Request attribute with the Subscription flag set.  The SW Request
   attribute is otherwise identical to the SW Requests discussed in
   previous sections.  Specifically, such a SW Request might or might
   not request inclusion of software inventory evidence records, might



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   or might not be targeted, and might request change event records or
   endpoint inventory.  Assuming no error is encountered, a SW-PC MUST
   send a SW Response attribute in direct response to this SW Request
   attribute, just as if the Subscription flag was not set.  As such,
   the attribute exchange that establishes a new subscription in a SW-PC
   has the same flow seen in the previous attribute exchanges, as
   depicted in Figure 2.  If the SW-PV does not receive a PA-TNC Error
   attribute (as described in Section 3.9 and Section 5.16) in response
   to their subscription request, the subscription has been successfully
   established on the SW-PC.  The SW Request attribute that establishes
   a new subscription is referred to as the "establishing request" for
   that subscription.

   When a subscription is established it is assigned a Subscription ID
   value.  The Subscription ID is equal to the value of the Request ID
   of the establishing request.  (For more about Request IDs, see
   Section 5.6.)

   A SW-PC MUST have the ability to record and support multiple
   simultaneous subscriptions from a single party and from multiple
   parties.  A SW-PV MUST have the ability to record and support
   multiple simultaneous subscriptions to a single party and
   subscriptions to multiple parties.

3.8.2.  Managing Subscriptions

   The SW-PC MUST record each accepted subscription along with the
   identity of the party to whom attributes are to be pushed in
   compliance with the subscription.  This identity includes both the
   NEA Server's connection ID and the Posture Validator Identifier from
   the PB-PA message that delivered the request.

   Likewise, SW-PVs MUST record each accepted subscription for which
   they are the subscribing party along with the associated Subscription
   ID and the identity of the SW-PC that will be fulfilling the
   subscription.  The SW-PV needs to retain this information in order to
   correctly interpret pushed SW Response attributes sent in fulfillment
   of the subscription.  The identity of the SW-PC is given in the
   Posture Collector Identifier of the PB-PA message header in all
   messages from that SW-PC.

3.8.3.  Terminating Subscriptions

   Subscriptions MAY be terminated at any time by the subscribing SW-PV
   by setting the Clear Subscriptions flag in a SW Request.  (See
   Section 5.7 for more on using this flag.)  In the case that a SW
   Request with the Clear Subscriptions flag set is received the SW-PC
   MUST only clear subscriptions that match both the NEA server



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   connection ID and the SW-PV ID for this SW Request, and MUST clear
   all such subscriptions.

   This specification does not give the SW-PV the ability to terminate
   subscriptions individually - all subscriptions to the SW-PV are
   cleared when the Clear Subscriptions flag is set.

   This specification does not give the SW-PC the ability to
   unilaterally terminate a subscription.  However, if the SW-PC
   experiences a fatal error fulfilling a subscription, resulting in
   sending a PA-TNC Error attribute of type
   SW_SUBSCRIPTION_FULFILLMENT_ERROR, then the subscription whose
   fulfillment led to the error MUST be treated as terminated by both
   the SW-PC and the SW-PV.  Only the subscription experiencing the
   error is cancelled and other subscriptions are unaffected.  See
   Section 3.9 for more on this error condition.

   Finally, a subscription is terminated if the connection between the
   SW-PC and SW-PV is deleted.  This occurs when the connection ID used
   in the messages between the SW-PC and the SW-PV becomes unbound.
   Loss of this connection ID would prevent the SW-PC from sending
   messages in fulfillment of this subscription.  As such, loss of the
   connection ID necessarily forces subscription termination between the
   affected parties.

3.8.4.  Subscription Status

   A SW-PV can request that a SW-PC report the list of active
   subscriptions for which the SW-PV is the subscriber.  A SW-PV can use
   this to recover lost information about active subscriptions.  A SW-PV
   can also use this capability to verify that a SW-PC has not forgotten
   any of its subscriptions.  The latter is especially useful where a
   SW-PC does not send any attributes in fulfillment of a given
   subscription for a long period of time.  The SW-PV can check the list
   of active subscriptions on the SW-PC and verify whether the
   inactivity is due to a lack of reportable events or due to the SW-PC
   forgetting its obligations to fulfill a given subscription.

   A SW-PV requests a list of its subscriptions on a given SW-PC by
   sending that SW-PC a Subscription Status Request.  The SW-PC MUST
   then respond with a Subscription Status Response (or a PA-TNC Error
   if an error condition is experienced).  The Subscription Status
   Response MUST contain one subscription record for each of the active
   subscriptions for which the SW-PV is the subscribing party.







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3.8.5.  Fulfilling Subscriptions

   As noted in Section 3.6 SW-PCs MUST have the ability to automatically
   detect changes to an endpoint's Software Inventory Evidence
   Collection in near real-time.  For every active subscription, the SW-
   PC MUST send an attribute to the subscribed SW-PV whenever a change
   is detected to relevant records within the endpoint's Software
   Inventory Evidence Collection.  Such an attribute is said to be sent
   "in fulfillment of" the given subscription and any such attribute
   MUST include that subscription's Subscription ID.  If the
   establishing request for that subscription was a targeted request,
   then only records that match the Software Identifiers provided in
   that establishing request are considered relevant.  Otherwise, (i.e.,
   for non-targeted requests) any record is considered relevant for this
   purpose.  Figure 3 shows a sample attribute exchange where a
   subscription is established and then later attributes are sent from
   the SW-PC in fulfillment of the established subscription.


            +-------------+                    +--------------+
            |   SW-PC     |                    |    SW-PV     |  Time
            +-------------+                    +--------------+   |
                  |                                   |           |
                  |<-----------SW Request-------------|           |
                  |                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           |
                  .                                   .           .
                  .                                   .           .
                  .                                   .           .
    <Change Event>|                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           |
                  .                                   .           .
                  .                                   .           .
                  .                                   .           .
    <Change Event>|                                   |           |
                  |------------SW Response----------->|           |
                  |                                   |           V


           Figure 3: Subscription Establishment and Fulfillment

   The contents of an attribute sent in fulfillment of a subscription
   depend on the parameters provided in the establishing request for
   that subscription.  Specifically, the contents of an attribute sent
   in fulfillment of a subscription have the same format as would a
   direct response to the establishing request.  For example, if the



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   establishing request stipulated a response that contained an event
   record list that included software inventory evidence records, all
   attributes sent in fulfillment of this subscription will also consist
   of event record lists with software inventory evidence records.  As
   such, all SW Responses displayed in the exchange depicted in Figure 3
   have the same format.  A SW Response generated in fulfillment of an
   active subscription MUST be a valid SW Response attribute according
   to all the rules outlined in the preceding sections.  In other words,
   an attribute constructed in fulfillment of a subscription will look
   the same as an attribute sent in direct response to an explicit
   request from a SW-PV that had the same request parameters and which
   arrived immediately after the given change event.  There are a few
   special rules that expand on this guideline:

3.8.5.1.  Subscriptions Reporting Inventories

   In the case that a SW-PV subscribes to a SW-PC requesting an
   inventory attribute whenever changes are detected (i.e. the EID in
   the establishing request is 0), then the SW-PC MUST send the
   requested inventory whenever a relevant change is detected.  (A
   "relevant change" is any change for untargeted requests, or a change
   to an indicated record in a targeted request.)  Upon detection of a
   relevant change for an active subscription, the SW-PC sends the
   appropriate inventory information as if it had just received the
   establishing request.  Attributes sent in fulfillment of this
   subscription will probably have a large amount of redundancy, as the
   same records are likely to be present in each of these SW Attributes.
   The role of an inventory subscription is not to report records just
   for the items that changed - that is the role of a subscription that
   reports events (see Section 3.8.5.2).  A SW-PC MUST NOT exclude a
   record from an attribute sent in fulfillment of an inventory
   subscription simply because that record was not involved in the
   triggering event (although a record might be excluded for other
   reasons, such as if the subscription is targeted - see
   Section 3.8.5.3).

3.8.5.2.  Subscriptions Reporting Events

   The way in which a SW-PV indicates it wishes to establish a
   subscription requesting event records is by providing a non-zero EID
   in the SW Request establishing the subscription (see Section 3.7.1).
   However, when the SW-PC constructs an attribute in fulfillment of the
   subscription (other than the direct response to the establishing
   request), it MUST only include event records for the detected
   change(s) that precipitated this response attribute.  In other words,
   it MUST NOT send a complete list of all changes starting with the
   indicated EID, up through the latest change, every time a new event
   is detected.  In effect, the EID in the establishing request is



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   treated as being updated every time an attribute is sent in
   fulfillment of this subscription, such that a single event is not
   reported twice in fulfillment of a single subscription.  As such,
   every SW-PC MUST track the EID of the last event that triggered an
   attribute for the given subscription.  When the next event (or set of
   events) is detected, the SW-PC MUST only report events with EIDs
   after the last reported event.  In the case that the EID Epoch of the
   SW-PC changes, the SW-PC MUST treat EID values in the new Epoch as
   being after all EIDs assigned in the previous Epoch regardless of the
   relative numeric values of these EIDs.

   Note that while a subscription is active, the subscribing SW-PV MAY
   make other requests for event records that overlap with events that
   are reported in fulfillment of a subscription.  Such requests are
   unaffected by the presence of the subscription, nor is the
   subscription affected by such requests.  In other words, a given
   request will get the same results back whether or not there was a
   subscription.  Likewise, an attribute sent in fulfillment of a
   subscription will contain the same information whether or not other
   requests had been received from the SW-PV.

   A SW-PV needs to pay attention to the EID Epoch in these attributes,
   as changes in the Epoch might create discontinuities in the SW-PV's
   understanding of the endpoint's Software Inventory Evidence
   Collection state, as discussed in Section 3.7.6.  In particular, once
   the EID Epoch changes, a SW-PV is unable have confidence that it has
   a correct understanding of the state of an endpoint's Software
   Inventory Evidence Collection until after the SW-PV collects a
   complete inventory.

   SW-PCs MAY send partial lists of event records in fulfillment of a
   subscription.  (See Section 3.7.5 for more on partial list of event
   records.)  In the case that a SW-PC sends a partial list of event
   records in fulfillment of a subscription, it MUST immediately send
   the next consecutive partial list, and continue doing so until it has
   sent the equivalent of the complete list of event records.  In other
   words, if the SW-PC sends a partial list it does not wait for another
   change event to send another SW Response, but continues sending SW
   Responses until it has sent all event records that would have been
   included in a complete fulfillment of the subscription.  Note that
   the direct response to the establishing request is not considered to
   be sent in fulfillment of a subscription.  However, in this case the
   SW-PC MUST treat the presence of unreported events as a triggering
   event for pushing additional messages in fulfillment of the newly
   established subscription.  As such, the net effect is that, if the
   direct response to the establishing request (i.e., the Subscription
   Fulfillment flag is unset) is partial, the SW-PC will immediately
   follow this with additional attributes (with the Subscription



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   Fulfillment flag set) until the complete set of events has been sent
   to the SW-PV.

3.8.5.3.  Targeted Subscriptions

   Subscriptions MAY be targeted to only apply to records that match a
   given set of Software Identifiers.  In the case where changes are
   detected that affect multiple records, some matching the establishing
   request's Software Identifiers and some not, the attribute sent in
   fulfillment of the subscription MUST only include inventory or events
   (as appropriate) for records that match the establishing request's
   Software Identifiers.  The SW-PC MUST NOT include non-matching
   records in the attribute, even if those non-matching records
   experienced change events that were co-temporal with change events on
   the matching records.

   In addition, a SW-PC MUST send an attribute in fulfillment of a
   targeted subscription only when changes to the endpoint's Software
   Inventory Evidence Collection impact one or more records matching the
   subscription's establishing request's Software Identifiers.  A SW-PC
   MUST NOT send any attribute in fulfillment of a targeted subscription
   based on detected change to the endpoint's Software Inventory
   Evidence Collection that did not involve any of the records targeted
   by that subscription.

3.8.5.4.  No Subscription Consolidation

   A SW-PV MAY establish multiple subscriptions to a given SW-PC.  If
   this is the case, it is possible that a single change event on the
   endpoint might require fulfillment by multiple subscriptions, and
   that the information included in attributes that fulfill each of
   these subscriptions might overlap.  The SW-PC MUST send separate
   attributes for each established subscription that requires a response
   due to the given event.  Each of these attributes MUST contain all
   information required to fulfill that individual subscription, even if
   that information is also sent in other attributes sent in fulfillment
   of other subscriptions at the same time.  In other words, SW-PCs MUST
   NOT attempt to combine information when fulfilling multiple
   subscriptions simultaneously, even if this results in some redundancy
   in the attributes sent to the SW-PV.

3.8.5.5.  Delayed Subscription Fulfillment

   A SW-PC MAY delay the fulfillment of a subscription following a
   change event in the interest of waiting to see if additional change
   events are forthcoming and, if so, conveying the relevant records
   back to the SW-PV in a single SW Response attribute.  This can help
   reduce network bandwidth consumption between the SW-PC and the SW-PV.



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   For example, consider a situation where 10 changes occur a tenth of a
   second apart.  If the SW-PC does not delay in assembling and sending
   SW Response attributes, the SW-PV will receive 10 separate SW
   Response attributes over a period of 1 second.  However, if the SW-PC
   waits half a second after the initial event before assembling a SW
   Response, the SW-PV only receives two SW Response attributes over the
   same period of time.

   Note that the ability to consolidate events for a single subscription
   over a given period of time does not contradict the rules in
   Section 3.8.5.4 prohibiting consolidation across multiple
   subscriptions.  When delaying fulfillment of subscriptions, SW-PCs
   are still required to fulfill each individual subscription
   separately.  Moreover, in the case that change events within the
   delay window cancel each other out (e.g., a record is deleted and
   then re-added), the SW-PC MUST still report each change event rather
   than just reporting the net effect of changes over the delay period.
   In other words, delayed fulfillment can decrease the number of
   attributes send by the SW-PC, but it does not reduce the total number
   of change events reported.

   SW-PCs are not required to support delayed fulfillment of
   subscriptions.  However, in the case that the SW-PC does support
   delayed subscription fulfillment, it MUST be possible to configure
   the SW-PC to disable delayed fulfillment.  In other words, parties
   deploying SW-PCs need to be allowed to disable delayed subscription
   fulfillment in their SW-PCs.  The manner in which such configuration
   occurs is left to the discretion of implementers, although
   implementers MUST protect the configuration procedure from
   unauthorized tampering.  In other words, there needs to be some
   assurance that unauthorized individuals are not able to introduce
   long delays in subscription fulfillment.

3.9.  Error Handling

   In the case where the SW-PC detects an error in a SW Request
   attribute that it receives it MUST respond with a PA-TNC Error
   attribute with an error code appropriate to the nature of the error.
   (See Section 4.2.8 of PA-TNC [RFC5792] for more details about PA-TNC
   Error attributes and error codes as well as Section 5.16 in this
   specification for error codes specific to SW Attributes.)  In the
   case that an error is detected in a SW Request the SW-PC MUST NOT
   take any action requested by this SW Request, even if partial
   completion of the SW is possible.  In other words, a SW Request that
   contains an error is completely ignored by the SW-PC (beyond sending
   a PA-TNC Error attribute, and possibly logging the error locally)
   rather than being partially executed.




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   In the case where the SW-PC receives a valid SW Request attribute but
   experiences an error during the process of responding to that
   attribute's instructions where that error prevents the SW-PC from
   properly or completely fulfilling that request, the SW-PC MUST send a
   PA-TNC Error attribute with an error code appropriate to the nature
   of the error.  In the case where a PA-TNC Error attribute is sent,
   the SW-PC MUST NOT take any of the actions requested by the SW
   Request attribute which led to the detected error.  This is the case
   even if some actions could have been completed successfully, and
   might even require the SW-PC to reverse some successful actions
   already taken before the error condition was detected.  In other
   words, either all aspects of a SW Request complete fully and
   successfully (in which case the SW-PC sends a SW Response attribute),
   or no aspects of the SW Request occur (in which case the SW-PC sends
   a PA-TNC Error attribute).  In the case that a SW-PC sends a PA-TNC
   Error attribute in response to a SW Request then the SW-PC MUST NOT
   also send any SW Response attribute in response to the same SW
   Request.  For this reason, the sending of a SW Response attribute
   MUST be the last action taken by a SW-PC in response to a SW Request
   to avoid the possibility of a processing error occurring after that
   SW Response attribute is sent.

   In the case that the SW-PC detects an error that prevents it from
   properly or completely fulfilling its obligations under an active
   subscription, the SW-PC MUST send a PA-TNC Error attribute of type
   SW_SUBSCRIPTION_FULFILLMENT_ERROR to the SW-PV that established this
   subscription.  This type of PA-TNC Error attribute identifies the
   specific subscription that cannot be adequately honored due to the
   error condition as well as an error "sub-type".  The error sub-type
   is used to indicate the type of error condition the SW-PC experienced
   that prevented it from honoring the given subscription.  In the case
   that the error condition cannot be identified or does not align with
   any of the defined error codes, the SW_ERROR error code SHOULD be
   used in the sub-type.  In the case that a
   SW_SUBSCRIPTION_FULFILLMENT_ERROR is sent, the associated
   subscription MUST be treated as cancelled by both the SW-PC and SW-
   PV.

   The SW-PV MUST NOT send any PA-TNC Error attributes to SW-PCs.  In
   the case that a SW-PV detects an error condition, it SHOULD log this
   error but does not inform any SW-PC's of this event.  Errors might
   include, but are not limited to, detection of malformed SW Response
   attributes sent from a given SW-PC, as well as detection of error
   conditions when the SW-PV processes SW Responses.

   Both SW-PCs and SW-PVs SHOULD log errors so that administrators can
   trace the causes of errors.  Log entries SHOULD include the type of
   the error, the time it was detected, and additional descriptive



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   information to aid in understanding the nature and cause of the
   error.

4.  Protocol

   The software inventory protocol supports two different types of
   message exchanges which are described the following subsections,
   along with implementation requirements for supporting these
   exchanges.

4.1.  Direct Response to a SW Request

   The first type of exchange is used to provide the SW-PV with a
   software inventory or event collection from the queried endpoint.


       +-------------+                      +--------------+
       |   SW-PC     |                      |    SW-PV     |  Time
       +-------------+                      +--------------+   |
             |                                     |           |
             |<------------SW Request--------------|           |
             |                                     |           |
             |             SW Response*            |           |
             |-----------------or----------------->|           |
             |             PA-TNC Error            |           |
             |                                     |           V

     *SW Response is one of the following: Software Identifier
      Inventory, Software Identifier Events, Software Inventory,
      or Software Events.


      Figure 4: SW Attribute Exchange (Direct Response to SW Request)

   In this exchange, the SW-PV indicates to the SW-PC, via a SW Request,
   the nature of the information it wishes to receive (inventory vs.
   events, full or targeted) and how it wishes the returned inventory to
   be expressed (with or without software inventory evidence records).
   The SW-PC responds with the requested information using the
   appropriate attribute type.  A single SW Request MUST only lead to a
   single SW Response or PA-TNC Error that is in direct response to that
   request.

4.2.  Subscription-Based Response

   The second type of exchange allows change event-based reporting based
   on a subscription.  If there is an active subscription on the
   endpoint, the SW-PC sends a SW Response to the SW-PV following a



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   change event on the endpoint in fulfillment of that subscription.
   Such an exchange is shown in Figure 5.


            +-------------+                +--------------+
            |   SW-PC     |                |    SW-PV     |  Time
            +-------------+                +--------------+   |
                  |                               |           |
    <Change Event>|                               |           |
                  |--------SW Response(s)*------->|           |
                  |                               |           |

     *SW Response is one of the following: Software Identifier
      Inventory, Software Identifier Events, Software Inventory,
      or Software Events.


       Figure 5: SW Attribute Exchange (In Fulfillment of an Active
                               Subscription)

   Note that, unlike direct responses to a SW Request, a single change
   event can precipitate multiple SW Responses for a single
   subscription, but only if all but the last of those SW Responses
   convey partial lists of event records.  When providing multiple SW
   Responses in this way, the initial responses contain partial lists of
   event records and the last of those SW Responses conveys the
   remainder of the relevant event records, completing the delivery of
   all relevant events in response to the change event.  A single Change
   Event MUST NOT otherwise be followed by multiple SW Response or PA-
   TNC Error attributes in any combination.

4.3.  Required Exchanges

   All SW-PVs and SW-PCs MUST support both types of exchanges.  In
   particular, SW-PCs MUST be capable of pushing a SW Response to a SW-
   PV immediately upon detection of a change to the endpoint's Software
   Inventory Evidence Collection in fulfillment of established SW-PV
   subscriptions, as described in Section 3.8.

5.  Software Inventory Messages and Attributes

   This section describes the format and semantics of the Software
   Inventory Message and Attributes for PA-TNC protocol.  This protocol
   uses the PA-TNC message header format [RFC5792].







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5.1.  PA Subtype (AKA PA-TNC Component Type)

   The NEA PB-TNC interface provides a general message-batching protocol
   capable of carrying one or more PA-TNC messages between the Posture
   Broker Client and Posture Broker Server.  When PB-TNC is carrying a
   PA-TNC message, the PB-TNC message headers contain a 32 bit
   identifier called the PA Subtype.  The PA Subtype field indicates the
   type of component associated with all of the PA-TNC attributes
   carried by the PB-TNC message.  The core set of PA Subtypes is
   defined in the PA-TNC specification.  This specification defines a
   new "SW Attributes" PA Subtype, which is registered in Section 10.1
   of this document, which is used as a namespace for the collection of
   SW attributes defined in this document.

   For more information on PB-TNC and PA-TNC messages and message
   headers, see the PB-TNC [RFC5793] and PA-TNC [RFC5792]
   specifications, respectively.

5.2.  SW Attribute Overview

   Each PA-TNC attribute described in this specification is intended to
   be sent between the SW-PC and SW-PV, so will be carried in a PB-TNC
   message indicating a PA Subtype of "SW Attributes".  PB-TNC messages
   MUST always include the SW Attributes Subtype defined in Section 5.1
   when carrying SW Attributes over PA-TNC.  The attributes defined in
   this specification appear below along with a short summary of their
   purposes.  Each attribute is described in greater detail in
   subsequent sections.

   SW Request:  This attribute is used to request a software inventory
     or software event list from an endpoint.  This attribute might also
     establish a subscription on the recipient SW-PC.  See Section 5.7
     for more information.

   Software Identifier Inventory:  This attribute is used to convey an
     inventory without the inclusion of software inventory evidence
     records.  See Section 5.8 for more information.

   Software Identifier Events:  This attribute is used to convey a list
     of events concerning changes to an endpoint's Software Inventory
     Evidence Collection.  Reported events do not include software
     inventory evidence records.  See Section 5.9 for more information.

   Software Inventory:  This attribute is used to convey an inventory
     expressed including software inventory evidence records.  See
     Section 5.10 for more information.





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   Software Events:  This attribute is used to convey a list of events
     concerning changes to an endpoint's inventory evidence collection.
     Reported events include software inventory evidence records.  See
     Section 5.11 for more information.

   Subscription Status Request:  This attribute is used to request a SW-
     PC send a summary of all the active subscriptions it has where the
     requesting party is the subscriber.  See Section 5.12 for more
     information.

   Subscription Status Response:  This attribute is used to convey
     information about the active subscriptions that a SW-PC has for a
     given subscriber.  See Section 5.13 for more information.

   Source Metadata Request:  This attribute is used to request a SW-PC
     send metadata about the sources is uses to collect software
     inventory information.  See Section 5.14 for more information.

   Source Metadata Response:  This attribute is used to convey
     descriptive metadata about the sources a SW-PC uses to collect
     software inventory information.  See Section 5.15 for more
     information.

   PA-TNC Error:  This is the standard PA-TNC Error attribute as defined
     in PA-TNC [RFC5792] and is used to indicate that an error was
     encountered during a software inventory exchange.  Use of the PA-
     TNC attribute by Software Inventory Message and Attributes for PA-
     TNC is described in Section 5.16.

   Because one of the Software Identifier Inventory, Software Identifier
   Events, Software Inventory, or Software Events attributes are
   expected to be sent to a SW-PV in direct response to a SW Request
   attribute or in fulfillment of an active subscription, those four
   attribute types are referred to collectively in this document as "SW
   Response attributes".

   All SW-PVs MUST be capable of sending SW Request attributes and be
   capable of receiving and processing all SW Response attributes as
   well as PA-TNC Error attributes.  All SW-PCs MUST be capable of
   receiving and processing SW Request attributes and be capable of
   sending all types of SW Response attributes as well as PA-TNC Error
   attributes.  In other words, both SW-PVs and SW-PCs are required to
   support their role in exchanges using any of the attribute types
   defined in this section.  SW-PVs MUST ignore any SW Request
   attributes that they receive.  SW-PCs MUST ignore any SW Response
   attributes or PA-TNC Error attributes that they receive.





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5.3.  Message Diagram Syntax

   This specification defines the syntax of new PA-TNC messages and
   attributes using diagrams.  Each diagram depicts the format and size
   of each field in bits.  Implementations MUST send the bits in each
   diagram as they are shown from left to right for each 32-bit quantity
   traversing the diagram from top to bottom.  Multi-octet fields
   representing numeric values MUST be sent in network (big endian) byte
   order.

   Descriptions of bit fields (e.g. flags) values refer to the position
   of the bit within the field.  These bit positions are numbered from
   the most significant bit through the least significant bit.  As such,
   an octet with only bit 0 set would have a value of 0x80 (1000 0000),
   an octet with only bit 1 set would have a value of 0x40 (0100 0000),
   and an octet with only bit 7 set would have a value of 0x01 (0000
   0001).

5.4.  Software Inventory Message and Attributes for PA-TNC Attribute
      Enumeration

   PA-TNC attribute types are identified in the PA-TNC Attribute Header
   via the Attribute Type Vendor ID and Attribute Type fields.  Table 2
   identifies the appropriate values for these fields for each attribute
   type used within the Software Inventory Message and Attributes for
   PA-TNC protocol.  The following is a summary of the registered
   attributes.  All attributes have a PEN value of 0x000000.  For the
   Integer value field, both the hexadecimal and decimal values are
   provided.

   +--------------+------------+---------------------------------------+
   | Attribute    | Integer    | Description                           |
   | Name         |            |                                       |
   +--------------+------------+---------------------------------------+
   | SW Request   | 0x00000011 | Request from a SW-PV to a SW-PC for   |
   |              | (17)       | the SW-PC to provide a software       |
   |              |            | inventory or event list               |
   |              |            |                                       |
   | Software     | 0x00000012 | An inventory sent without software    |
   | Identifier   | (18)       | inventory evidence records sent from  |
   | Inventory    |            | a SW-PC.                              |
   |              |            |                                       |
   | Software     | 0x00000013 | A collection of events impacting the  |
   | Identifier   | (19)       | endpoint's Software Inventory         |
   | Events       |            | Evidence Collection, where events do  |
   |              |            | not include software inventory        |
   |              |            | evidence records.                     |
   |              |            |                                       |



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   | Software     | 0x00000014 | An inventory including software       |
   | Inventory    | (20)       | inventory evidence records sent from  |
   |              |            | a SW-PC.                              |
   |              |            |                                       |
   | Software     | 0x00000015 | A collection of events impacting the  |
   | Events       | (21)       | endpoint's Software Inventory         |
   |              |            | Evidence Collection, where events     |
   |              |            | include software inventory evidence   |
   |              |            | records.                              |
   |              |            |                                       |
   | Subscription | 0x00000016 | A request for a list of a SW-PV's     |
   | Status       | (22)       | active subscription on a SW-PC.       |
   | Request      |            |                                       |
   |              |            |                                       |
   | Subscription | 0x00000017 | A list of a SW-PV's active            |
   | Status       | (23)       | subscriptions on a SW-PC.             |
   | Response     |            |                                       |
   |              |            |                                       |
   | Source       | 0x00000018 | A request for information about a SW- |
   | Metadata     | (24)       | PC's data sources.                    |
   | Request      |            |                                       |
   |              |            |                                       |
   | Subscription | 0x00000019 | Descriptive metadata about a SW-PC's  |
   | Status       | (25)       | data sources.                         |
   | Response     |            |                                       |
   |              |            |                                       |
   | Reserved     | 0x0000001A | These attribute types are reserved    |
   |              | -          | for future use in revisions to        |
   |              | 0x0000001F | Software Inventory Message and        |
   |              | (26 - 31)  | Attributes for PA-TNC.                |
   |              |            |                                       |
   | PA-TNC Error | 0x00000008 | An error attribute as defined in the  |
   |              | (8)        | PA-TNC specification [RFC5792].       |
   +--------------+------------+---------------------------------------+

                     Table 2: SW Attribute Enumeration

5.5.  Normalization of Text Encoding

   In order to ensure consistency of transmitted attributes some fields
   require normalization of their format.  When this is necessary, this
   is indicated in the field's description.  In such cases, the field
   contents MUST be normalized to Network Unicode format as defined in
   RFC 5198 [RFC5198].  Network Unicode format defines a refinement of
   UTF-8 that ensures a normalized expression of characters.  SW-PCs and
   SW-PVs MUST NOT perform conversion and normalization on any field
   values except those specifically identified as requiring
   normalization in the following sections.  Note, however, that some



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   data models require additional normalization before source
   information is added to an Endpoint's Inventory Evidence Collection
   as a record.  The references from the Software Data Model IANA table
   (see Section 10.4) will note where this is necessary.

5.6.  Request IDs

   All SW Request attributes MUST include a Request ID value.  The
   Request ID field provides a value that identifies a given request
   relative to other requests between a SW-PV and the receiving SW-PC.
   Specifically, the SW-PV assigns each SW Request attribute a Request
   ID value that is intended to be unique within the lifetime of a given
   network connection ID as assigned by the SW-PV's Posture Broker
   Server.

   In the case that a SW Request requests the establishment of a
   subscription and the receiving SW-PC agrees to that subscription, the
   Request ID of that SW Request (i.e., the establishing request of the
   subscription) becomes that subscription's Subscription ID.  All
   attributes sent in fulfillment of this subscription include a flag
   indicating that the attribute fulfills a subscription and the
   subscription's Subscription ID.  A SW-PV MUST NOT reuse a Request ID
   value in communicating to a given SW-PC while that Request ID is also
   serving as a Subscription ID for an active subscription with that SW-
   PC.  In the case where a SW-PC receives a SW Request from a given SW-
   PV where that Request ID is also the Subscription ID of an active
   subscription with that SW-PV, the SW-PC MUST respond with a PA-TNC
   Error attribute with an error code of SW_SUBSCRIPTION_ID_REUSE_ERROR.
   Note that this error does not cancel the indicated subscription.

   Subscription Status Requests and Subscription Status Responses do not
   include Request IDs.

   In the case where all possible Request ID values have been exhausted
   within the lifetime of a single network connection ID, the sender MAY
   reuse previously used Request IDs within the same network connection
   if the ID is not being used as a Subscription ID.  In such a case of
   Request ID reuse, Request IDs SHOULD be reused in the order of their
   original use.  In other words, a SW-PC SHOULD NOT use a given Request
   ID value more than once within a persistent connection between a
   given Posture Broker Client-Posture Broker Server pair.  In the case
   where reuse is necessary due to exhaustion of possible ID values, the
   SW-PC SHOULD structure the reuse to maximize the time between
   original and subsequent use.  The Request ID value is included in a
   SW Response attribute directly responding to this SW Request to
   indicate which SW Request was received and caused the response.
   Request IDs can be randomly generated or sequential, as long as




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   values are not repeated per the rules in this paragraph.  SW-PCs are
   not required to check for duplicate Request IDs.

5.7.  SW Request

   A SW-PV sends this attribute to a SW-PC to request that the SW-PC
   send software inventory information to the SW-PV.  A SW-PC MUST NOT
   send this attribute.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |       Software Identifier Count               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Request ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Earliest EID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Software Identifier Length  | Software Identifier (var len) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



                      Figure 6: SW Request Attribute

   +---------------+---------------------------------------------------+
   | Field         | Description                                       |
   +---------------+---------------------------------------------------+
   | Flags: Bit 0  | If set (1), the SW-PC MUST delete all             |
   | - Clear       | subscriptions established by the requesting SW-PV |
   | Subscriptions | (barring any errors).                             |
   |               |                                                   |
   | Flags: Bit 1  | If set (1), in addition to responding to the      |
   | - Subscribe   | request as described, the SW-PC MUST establish a  |
   |               | subscription with parameters matching those in    |
   |               | the request attribute (barring any errors).       |
   |               |                                                   |
   | Flags: Bit 2  | If unset (0), the SW-PC's response MUST include   |
   | - Result Type | software inventory evidence records and thus the  |
   |               | response MUST be a Software Inventory, a Software |
   |               | Events, or a PA-TNC Error attribute. If set (1),  |
   |               | the response MUST NOT include software inventory  |
   |               | evidence records and thus the response MUST be a  |
   |               | Software Identifier Inventory, a Software         |
   |               | Identifier Events, or a PA-TNC Error attribute.   |
   |               |                                                   |
   | Flags: Bit    | Reserved for future use. This field MUST be set   |



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   | 3-7 -         | to zero on transmission and ignored upon          |
   | Reserved      | reception.                                        |
   |               |                                                   |
   | Software      | A 3-byte unsigned integer indicating the number   |
   | Identifier    | of Software Identifiers that follow. If this      |
   | Count         | value is non-zero, this is a targeted request, as |
   |               | described in Section 3.5.  The Software           |
   |               | Identifier Length and Software Identifier fields  |
   |               | are repeated, in order, the number of times       |
   |               | indicated in this field. In the case where        |
   |               | Software Identifiers are present, the SW-PC MUST  |
   |               | only report software that corresponds to the      |
   |               | identifiers the SW-PV provided in this attribute  |
   |               | (or with a PA-TNC Error attribute).  This field   |
   |               | value MAY be 0, in which case there are no        |
   |               | instances of the Software Identifier Length and   |
   |               | Software Identifier fields. In this case, the SW- |
   |               | PV is indicating an interest in all software      |
   |               | inventory evidence records on the endpoint (i.e., |
   |               | this is not a targeted request).                  |
   |               |                                                   |
   | Request ID    | A value that uniquely identifies this SW Request  |
   |               | from a particular SW-PV.                          |
   |               |                                                   |
   | Earliest EID  | In the case where the SW-PV is requesting         |
   |               | software events, this field contains the EID      |
   |               | value of the earliest event the SW-PV wishes to   |
   |               | have reported. (Note - the report will be         |
   |               | inclusive of the event with this EID value.) In   |
   |               | the case where the SW-PV is requesting an         |
   |               | inventory, then this field MUST be 0.             |
   |               | (0x00000000) In the case where this field is non- |
   |               | zero, the SW-PV is requesting events and the SW-  |
   |               | PC MUST respond using a Software Events, Software |
   |               | Identifier Events, or a PA-TNC Error attribute.   |
   |               | In the case where this field is zero, the SW-PV   |
   |               | is requesting an inventory and the SW-PC MUST     |
   |               | respond using a Software Inventory, a Software    |
   |               | Identifier Inventory, or a PA-TNC Error           |
   |               | attribute.                                        |
   |               |                                                   |
   | Software      | A 2-byte unsigned integer indicating the length   |
   | Identifier    | in bytes of the Software Identifier field.        |
   | Length        |                                                   |
   |               |                                                   |
   | Software      | A string containing the Software Identifier value |
   | Identifier    | from a software inventory evidence record. This   |
   |               | field value MUST be normalized to Network Unicode |



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   |               | format, as described in Section 5.5.  This string |
   |               | MUST NOT be NULL terminated.                      |
   +---------------+---------------------------------------------------+

                   Table 3: SW Request Attribute Fields

   The SW-PV sends the SW Request attribute to a SW-PC to request the
   indicated information.  Note that between the Result Type flag and
   the Earliest EID field, the SW-PC is constrained to a single possible
   SW Response attribute type (or a PA-TNC Error attribute) in its
   response to the request.

   The Subscribe and Clear Subscription flags are used to manage
   subscriptions for the requesting SW-PV on the receiving SW-PC.
   Specifically, an attribute with the Subscribe flag set seeks to
   establish a new subscription by the requesting SW-PV to the given SW-
   PC, while an attribute with the Clear Subscription flag seeks to
   delete all existing subscriptions by the requesting SW-PV on the
   given SW-PC.  Note that, in the latter case, only the subscriptions
   associated with the Connection ID and the Posture Validator ID of the
   requester are deleted as described in Section 3.8.3.  A newly
   established subscription has the parameters outlined in the Request
   attribute.  Specifically, the Result Type flag indicates the type of
   result to send in fulfillment of the subscription, the value of the
   Earliest EID field indicates whether the fulfillment attributes list
   inventories or events, and the fields describing Software Identifiers
   (if present) indicate if and how a subscription is targeted.  In the
   case that the SW-PC is unable or unwilling to comply with the SW-PV's
   request to establish or clear subscriptions, the SW-PC MUST respond
   with a PA-TNC Error attribute with the SW_SUBSCRIPTION_DENIED_ERROR
   error code.  If the SW-PV requests that subscriptions be cleared but
   has no existing subscriptions, this is not an error.

   An attribute requesting the establishment of a subscription is
   effectively doing double-duty, as it is a request for an immediate
   response from the SW-PC in addition to setting up the subscription.
   Assuming the SW-PC is willing to comply with the subscription it MUST
   send an appropriate response attribute to a request with the
   Subscribe flag set containing all requested information.  The same is
   true of the Clear Subscription flag - assuming there is no error the
   SW-PC MUST generate a response attribute without regard to the
   presence of this flag in addition to clearing its subscription list.

   Both the Subscribe and Clear Subscription flags MAY be set in a
   single SW Request attribute.  In the case where this request is
   successful, the end result MUST be equivalent to the SW-PC clearing
   its subscription list for the given SW-PV first and then creating a
   new subscription in accordance with the request parameters.  In other



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   words, do not first create the new subscription and then clear all
   the subscriptions including the one that was just created.  In the
   case that the requested actions are successfully completed, the SW-PC
   MUST respond with a SW Response attribute.  The specific type of SW
   Response attribute depends on the Result Type and Earliest EID
   fields, as described above.  In the case where there is a failure
   that prevents some part this request from completing, the SW-PC MUST
   NOT add a new subscription, MUST NOT clear the old subscriptions, and
   the SW-PC MUST respond with a PA-TNC Error attribute.  In other
   words, the SW-PC MUST NOT partially succeed at implementing such a
   request; either all actions succeed, or none succeed.

   The Earliest EID field is used to indicate if the SW-PV is requesting
   an inventory or event list from the SW-PC.  A value of 0 (0x00000000)
   represents a request for inventory information.  Otherwise, the SW-PV
   is requesting event information.  For Earliest EID values other than
   0, the SW-PC's response MUST respond with event records, as described
   in Section 3.7.  Note that the request does not identify a particular
   EID Epoch, since responses can only include events in the SW-PC's
   current EID Epoch.

   The Software Identifier Count indicates the number of Software
   Identifiers in the attribute.  This number might be any value between
   0 and 16,777,216, inclusive.  A single Software Identifier is
   represented by the following fields: Software Identifier Length and
   Software Identifier.  These fields are repeated a number of times
   equal to the Software Identifier Count, which may be 0.  The Software
   Identifier Length field indicates the number of bytes allocated to
   the Software Identifier field.  The Software Identifier field
   contains a Software Identifier as describe in Section 3.4.1.  The
   presence of one or more Software Identifiers is used by the SW-PV to
   indicate a targeted request, which seeks only inventories of or
   events affecting software corresponding to the given identifiers.
   The SW-PC MUST only report software that matched the Software
   Identifiers provided in the SW-PVs SW Request attribute.

5.8.  Software Identifier Inventory

   A SW-PC sends this attribute to a SW-PV to convey the inventory of
   the endpoint's Software Inventory Evidence Collection without the
   inclusion of software inventory evidence records.  This list might
   represent a complete inventory or a targeted list of records,
   depending on the parameters in the SW-PV's request.  A SW-PV MUST NOT
   send this attribute.  The SW-PC either sends this attribute in
   fulfillment of an existing subscription where the establishing
   request has a Result Type of 1 and the Earliest EID is zero, or in
   direct response to a SW Request attribute where the Result Type is 1
   and the Earliest EID is zero.



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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |         Software Identifier Count             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Request ID Copy / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        EID Epoch                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Last EID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Record Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Data Model Type PEN                 |Data Model Type|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Software Identifier Length  |   Software Locator Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Source Id Num |     Software Identifier (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Software Locator (variable length)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



             Figure 7: Software Identifier Inventory Attribute

   +----------------+--------------------------------------------------+
   | Field          | Description                                      |
   +----------------+--------------------------------------------------+
   | Flags: Bit 0 - | In the case that this attribute is sent in       |
   | Subscription   | fulfillment of a subscription this bit MUST be   |
   | Fulfillment    | set (1).  In the case that this attribute is a   |
   |                | direct response to a SW Request, this bit MUST   |
   |                | be unset (0).                                    |
   |                |                                                  |
   | Flags: Bit 1-7 | Reserved for future use. This field MUST be set  |
   | - Reserved     | to zero on transmission and ignored upon         |
   |                | reception.                                       |
   |                |                                                  |
   | Software       | The number of Software Identifiers that follow.  |
   | Identifier     | This field is an unsigned integer. The Record    |
   | Count          | Identifier, Data Model Type PEN, Data Model      |
   |                | Type, Software Identifier Length, Software       |
   |                | Locator Length, Source Identification Number,    |
   |                | Software Identifier, and Software Locator fields |
   |                | are repeated, in order, the number of times      |
   |                | indicated in this field. This field value MAY be |
   |                | 0, in which case there are no instances of these |



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   |                | fields.                                          |
   |                |                                                  |
   | Request ID     | In the case where this attribute is in direct    |
   | Copy /         | response to a SW Request attribute from a SW-PV, |
   | Subscription   | this field MUST contain an exact copy of the     |
   | ID             | Request ID field from that SW Request.  In the   |
   |                | case where this attribute is sent in fulfillment |
   |                | of an active subscription, this field MUST       |
   |                | contain the Subscription ID of the subscription  |
   |                | being fulfilled by this attribute.               |
   |                |                                                  |
   | EID Epoch      | The EID Epoch of the Last EID value. This field  |
   |                | is an unsigned 4-byte integer.                   |
   |                |                                                  |
   | Last EID       | The EID of the last event recorded by the SW-PC, |
   |                | or 0 if the SW-PC has no recorded events. This   |
   |                | field is an unsigned 4-byte integer.             |
   |                |                                                  |
   | Record         | A 4-byte, unsigned integer containing the Record |
   | Identifier     | Identifier value from a software inventory       |
   |                | evidence record.                                 |
   |                |                                                  |
   | Data Model     | A 3-byte unsigned integer containing the Private |
   | Type PEN       | Enterprise Number (PEN) of the organization that |
   |                | assigned the meaning of the Data Model Type      |
   |                | value.                                           |
   |                |                                                  |
   | Data Model     | A 1-byte unsigned integer containing an          |
   | Type           | identifier number that identifies the data model |
   |                | of the reported record.                          |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Identifier     | in bytes of the SW ID field.                     |
   | Length         |                                                  |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Locator Length | in bytes of the Software Locator field.          |
   |                |                                                  |
   | Source         | The Source Identification Number associated with |
   | Identification | the source from which this software installation |
   | Number         | inventory instance was reported.                 |
   |                |                                                  |
   | Software       | A string containing the Software Identifier      |
   | Identifier     | value from a software inventory evidence record. |
   |                | This field value MUST be normalized to Network   |
   |                | Unicode format, as described in Section 5.5.     |
   |                | This string MUST NOT be NULL terminated.         |
   |                |                                                  |



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   | Software       | A string containing the Software Locator value.  |
   | Locator        | This is expressed as a URI. This field value     |
   |                | MUST be normalized to Network Unicode format as  |
   |                | described in Section 3.4.4. This string MUST NOT |
   |                | be NULL terminated.                              |
   +----------------+--------------------------------------------------+

          Table 4: Software Identifier Inventory Attribute Fields

   In the case that this attribute is sent in fulfillment of a
   subscription, the Subscription Fulfillment bit MUST be set (1).  In
   the case that this attribute is sent in direct response to a SW
   Request, the Subscription Fulfillment bit MUST be unset (0).  Note
   that the SW Response attribute sent in direct response to a SW
   Request that establishes a subscription (i.e., a subscription's
   establishing request) MUST be treated as a direct response to that SW
   Request (and thus the Subscription Fulfillment bit is unset).  SW
   Response attributes are only treated as being in fulfillment of a
   subscription (i.e., Subscription Fulfillment bit set) if they are
   sent following a change event, as shown in Figure 3.

   The Software Identifier Count field indicates the number of Software
   Identifiers present in this inventory.  Each Software Identifier is
   represented by the following set of fields: Record Identifier, Data
   Model Type, Software Identifier Length, SW ID, Software Locator
   Length, and Software Locator.  These fields will appear once for each
   reported record.

   When responding directly to a SW Request attribute, the Request ID
   Copy / Subscription ID field MUST contain an exact copy of the
   Request ID field from that SW Request.  When this attribute is sent
   in fulfillment of an existing subscription on this Posture Collector,
   then this field MUST contain the Subscription ID of the fulfilled
   subscription.

   The EID Epoch field indicates the EID Epoch of the Last EID value.
   The Last EID field MUST contain the EID of the last recorded change
   event (see Section 3.7 for more about EIDs and recorded events) at
   the time this inventory was collected.  In the case where there are
   no recorded change events at the time that this inventory was
   collected, the Last EID field MUST contain 0.  These fields can be
   interpreted to indicate that the provided inventory reflects the
   state of the endpoint after all changes up to and including this last
   event have been accounted for.

   The Data Model Type PEN and Data Model Type fields are used to
   identify the data model associated with the given software record.
   These fields are discussed more in Section 3.4.2.



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   The Source Identification Number field is used to identify the source
   that provided the given record, as described in Section 3.1.

5.9.  Software Identifier Events

   A SW-PC sends this attribute to a SW-PV to convey events where the
   affected records are reported without software inventory evidence
   records.  A SW-PV MUST NOT send this attribute.  The SW-PC either
   sends this attribute in fulfillment of an existing subscription where
   the establishing request has a Result Type is 1 and the Earliest EID
   is non-zero, or in direct response to a SW Request attribute where
   the Result Type is 1 and the Earliest EID is non-zero.







































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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags        |                Event Count                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request ID Copy / Subscription ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       EID Epoch                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Last EID                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Last Consulted EID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          EID                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timestamp                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Record Identifier                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Data Model Type PEN                 |Data Model Type|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Software Identifier Length  |   Software Locator Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Source Id Num |  Action       | Software Identifier (var len) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Software Locator (variable length)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 8: Software Identifier Events Attribute

   +----------------+--------------------------------------------------+
   | Field          | Description                                      |
   +----------------+--------------------------------------------------+
   | Flags: Bit 0 - | In the case that this attribute is sent in       |
   | Subscription   | fulfillment of a subscription this bit MUST be   |
   | Fulfillment    | set (1).  In the case that this attribute is a   |
   |                | direct response to a SW Request, this bit MUST   |
   |                | be unset (0).                                    |
   |                |                                                  |



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   | Flags: Bit 1-7 | Reserved for future use. This field MUST be set  |
   | - Reserved     | to zero on transmission and ignored upon         |
   |                | reception.                                       |
   |                |                                                  |
   | Event Count    | The number of events that are reported in this   |
   |                | attribute. This field is a 3-byte unsigned       |
   |                | integer.  The EID, Timestamp, Record Identifier, |
   |                | Data Model Type PEN, Data Model Type, Software   |
   |                | Identifier Length, Software Locator Length,      |
   |                | Source Identification Number, Action, Software   |
   |                | Identifier, and Software Locator fields are      |
   |                | repeated, in order, the number of times          |
   |                | indicated in this field. This field value MAY be |
   |                | 0, in which case there are no instances of these |
   |                | fields.                                          |
   |                |                                                  |
   | Request ID     | In the case where this attribute is in direct    |
   | Copy /         | response to a SW Request attribute from a SW-PV, |
   | Subscription   | this field MUST contain an exact copy of the     |
   | ID             | Request ID field from that SW Request.  In the   |
   |                | case where this attribute is sent in fulfillment |
   |                | of an active subscription, this field MUST       |
   |                | contain the Subscription ID of the subscription  |
   |                | being fulfilled by this attribute.               |
   |                |                                                  |
   | EID Epoch      | The EID Epoch of the Last EID value. This field  |
   |                | is an unsigned 4-byte integer.                   |
   |                |                                                  |
   | Last EID       | The EID of the last event recorded by the SW-PC, |
   |                | or 0 if the SW-PC has no recorded events. This   |
   |                | field contains the EID of the SW-PC's last       |
   |                | recorded change event (which might or might not  |
   |                | be included as an event record in this           |
   |                | attribute).                                      |
   |                |                                                  |
   | Last Consulted | The EID of the last event record that was        |
   | EID            | consulted when generating the event record list  |
   |                | included in this attribute. This is different    |
   |                | from the Last EID field value if and only if     |
   |                | this attribute is conveying a partial list of    |
   |                | event records. See Section 3.7.5 for more on     |
   |                | partial list of event records.                   |
   |                |                                                  |
   | EID            | The EID of the event in this event record.       |
   |                |                                                  |
   | Timestamp      | The timestamp associated with the event in this  |
   |                | event record. This timestamps is the SW-PC's     |
   |                | best understanding of when the given event       |



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   |                | occurred. Note that this timestamp might be an   |
   |                | estimate.  The Timestamp date and time MUST be   |
   |                | represented as an RFC 3339 [5] compliant ASCII   |
   |                | string in Coordinated Universal Time (UTC) time  |
   |                | with the additional restrictions that the 'T'    |
   |                | delimiter and the 'Z' suffix MUST be capitalized |
   |                | and fractional seconds (time-secfrac) MUST NOT   |
   |                | be included. This field conforms to the date-    |
   |                | time ABNF production from section 5.6 of RFC     |
   |                | 3339 [RFC3339] with the above restrictions.      |
   |                | Leap seconds are permitted and SW-PVs MUST       |
   |                | support them.  The Timestamp string MUST NOT be  |
   |                | NULL terminated or padded in any way. The length |
   |                | of this field is always 20 octets.               |
   |                |                                                  |
   | Record         | A 4-byte, unsigned integer containing the Record |
   | Identifier     | Identifier value from a software inventory       |
   |                | evidence record.                                 |
   |                |                                                  |
   | Data Model     | A 3-byte unsigned integer containing the Private |
   | Type PEN       | Enterprise Number (PEN) of the organization that |
   |                | assigned the meaning of the Data Model Type      |
   |                | value.                                           |
   |                |                                                  |
   | Data Model     | A 1-byte unsigned integer containing an          |
   | Type           | identifier number that identifies the data model |
   |                | of the reported record.                          |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Identifier     | in bytes of the SW ID field.                     |
   | Length         |                                                  |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Locator Length | in bytes of the Software Locator field.          |
   |                |                                                  |
   | Source         | The Source Identification Number associated with |
   | Identification | the source from which this software installation |
   | Number         | inventory instance was reported.                 |
   |                |                                                  |
   | Action         | The type of event that is recorded in this event |
   |                | record. Possible values are: 1 = CREATION - the  |
   |                | addition of a record to the endpoint's Software  |
   |                | Inventory Evidence Collection; 2 = DELETION -    |
   |                | the removal of a record from the endpoint's      |
   |                | Software Inventory Evidence Collection; 3 =      |
   |                | ALTERATION - There was an alteration to a record |
   |                | within the endpoint's Software Inventory         |
   |                | Evidence Collection. All other values are        |



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   |                | reserved for future use and MUST NOT be used     |
   |                | when sending attributes. In the case where a SW- |
   |                | PV receives an event record that uses an action  |
   |                | value other than the ones defined here, it MUST  |
   |                | ignore that event record but SHOULD process      |
   |                | other event records in this attribute as normal. |
   |                |                                                  |
   | Software       | A string containing the Software Identifier      |
   | Identifier     | value from a software inventory evidence record. |
   |                | This field value MUST be normalized to Network   |
   |                | Unicode format, as described in Section 5.5.     |
   |                | This string MUST NOT be NULL terminated.         |
   |                |                                                  |
   | Software       | A string containing the Software Locator value.  |
   | Locator        | This is expressed as a URI. This field value     |
   |                | MUST be normalized to Network Unicode format as  |
   |                | described in Section 3.4.4. This string MUST NOT |
   |                | be NULL terminated.                              |
   +----------------+--------------------------------------------------+

           Table 5: Software Identifier Events Attribute Fields

   The first few fields in the Software Identifier Events attribute
   mirror those in the Software Identifier Inventory attribute.  The
   primary difference is that, instead of conveying an inventory, the
   attribute conveys zero or more event records, consisting of the EID,
   timestamp, Record Identifier, action type, data model type, Software
   Identifier, and Software Locator of the affected software inventory
   evidence record.

   With regard to the Timestamp field, it is important to note that
   clock skew between the SW-PC and SW-PV as well as between different
   SW-PCs within an enterprise might make correlation of timestamp
   values difficult.  This specification does not attempt to resolve
   clock skew issues, although other mechanisms outside of this
   specification do exist to reduce the impact of clock skew and make
   the timestamp more useful for such correlation.  Instead, Software
   Inventory Message and Attributes for PA-TNC uses Timestamp value
   primarily as a means to indicate the amount of time between two
   events on a single endpoint.  For example, by taking the difference
   of the times for when a record was removed and then subsequently re-
   added, one can get an indication as to how long the system was
   without the given record (and, thus without the associated software).
   Since this will involve comparison of timestamp values all
   originating on the same system, clock skew between the SW-PC and SW-
   PV is not an issue.  However, if the SW-PC's clock was adjusted
   between two recorded events, it is possible for such a calculation to
   lead to incorrect understandings of the temporal distance between



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   events.  Users of this field need to be aware of the possibility for
   such occurrences.  In the case where the Timestamp values of two
   events appear to contradict the EID ordering of those events (i.e.,
   the later EID has an earlier timestamp) the recipient MUST treat the
   EID ordering as correct.

   All events recorded in a Software Identifier Events Attribute are
   required to be part of the same EID Epoch.  Specifically, all
   reported events MUST have an EID from the same EID Epoch as each
   other, and which is the same as the EID Epoch of the Last EID and
   Last Consulted EID values.  The SW-PC MUST NOT report events with
   EIDs from different EID Epochs.

   The Last Consulted EID field contains the EID of the last event
   record considered for inclusion in this attribute.  If this attribute
   contains a partial event set (as described in Section 3.7.5) this
   field value will be less than the Last EID value; if this attribute
   contains a complete event set, the Last EID and Last Consulted EID
   values are identical.

   If multiple events are sent in a Software Identifier Events
   attribute, the order in which they appear within the attribute is not
   significant.  The EIDs associated with them are used for ordering the
   indicated events appropriately.  Also note that a single software
   record might be reported multiple times in an attribute, such as if
   multiple events involving the associated record were being reported.

5.10.  Software Inventory

   A SW-PC sends this attribute to a SW-PV to convey a list of inventory
   records.  A SW-PV MUST NOT send this attribute.  The SW-PC either
   sends this attribute in fulfillment of an existing subscription where
   the establishing request had a Result Type of 0 and the Earliest EID
   is zero, or in direct response to a SW Request attribute where the
   Result Type is 0 and the Earliest EID is zero.
















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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Flags         |             Record Count                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Request ID Copy / Subscription ID              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            EID Epoch                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Last EID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Record Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Data Model Type PEN                 |Data Model Type|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Software Identifier Length      |  Software Locator Length    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Record Length                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Source Id Num |       Software Identifier (variable length)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Software Locator (Variable length)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Record (Variable length)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 9: Software Inventory Attribute

   +----------------+--------------------------------------------------+
   | Field          | Description                                      |
   +----------------+--------------------------------------------------+
   | Flags: Bit 0 - | In the case that this attribute is sent in       |
   | Subscription   | fulfillment of a subscription this bit MUST be   |
   | Fulfillment    | set (1).  In the case that this attribute is a   |
   |                | direct response to a SW Request, this bit MUST   |
   |                | be unset (0).                                    |
   |                |                                                  |
   | Flags: Bit 1-7 | Reserved for future use. This field MUST be set  |
   | - Reserved     | to zero on transmission and ignored upon         |
   |                | reception.                                       |
   |                |                                                  |
   | Record Count   | The number of records that follow. This field is |
   |                | a 3-byte unsigned integer. The Record            |
   |                | Identifier, Data Model Type PEN, Data Model      |
   |                | Type, Software Identifier Length, Software       |
   |                | Locator Length, Record Length, Source            |
   |                | Identification Number, Software Identifier,      |



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   |                | Software Locator, and Record fields are          |
   |                | repeated, in order, the number of times          |
   |                | indicated in this field. This field value MAY be |
   |                | 0 in which case there are no instances of these  |
   |                | fields.                                          |
   |                |                                                  |
   | Request ID     | In the case where this attribute is in direct    |
   | Copy /         | response to a SW Request attribute from a SW-PV, |
   | Subscription   | this field MUST contain an exact copy of the     |
   | ID             | Request ID field from that SW Request.  In the   |
   |                | case where this attribute is sent in fulfillment |
   |                | of an active subscription, this field MUST       |
   |                | contain the Subscription ID of the subscription  |
   |                | being fulfilled by this attribute.               |
   |                |                                                  |
   | EID Epoch      | The EID Epoch of the Last EID value. This field  |
   |                | is an unsigned 4-byte integer.                   |
   |                |                                                  |
   | Last EID       | The EID of the last event recorded by the SW-PC, |
   |                | or 0 if the SW-PC has no recorded events. This   |
   |                | field is an unsigned 4-byte integer.             |
   |                |                                                  |
   | Record         | A 4-byte, unsigned integer containing the Record |
   | Identifier     | Identifier value from a software inventory       |
   |                | evidence record.                                 |
   |                |                                                  |
   | Data Model     | A 3-byte unsigned integer containing the Private |
   | Type PEN       | Enterprise Number (PEN) of the organization that |
   |                | assigned the meaning of the Data Model Type      |
   |                | value.                                           |
   |                |                                                  |
   | Data Model     | A 1-byte unsigned integer containing an          |
   | Type           | identifier number that identifies the data model |
   |                | of the reported record.                          |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Identifier     | in bytes of the SW ID field.                     |
   | Length         |                                                  |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Locator Length | in bytes of the Software Locator field.          |
   |                |                                                  |
   | Record Length  | This is a 4-byte unsigned integer indicating the |
   |                | length of the Record field in bytes.             |
   |                |                                                  |
   | Source         | The Source Identification Number associated with |
   | Identification | the source from which this software installation |
   | Number         | inventory instance was reported.                 |



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   |                |                                                  |
   | Software       | A string containing the Software Identifier      |
   | Identifier     | value from a software inventory evidence record. |
   |                | This field value MUST be normalized to Network   |
   |                | Unicode format, as described in Section 5.5.     |
   |                | This string MUST NOT be NULL terminated.         |
   |                |                                                  |
   | Software       | A string containing the Software Locator value.  |
   | Locator        | This is expressed as a URI. This field value     |
   |                | MUST be normalized to Network Unicode format as  |
   |                | described in Section 3.4.4. This string MUST NOT |
   |                | be NULL terminated.                              |
   |                |                                                  |
   | Record         | A software inventory evidence record as a        |
   |                | string. The record MUST be converted and         |
   |                | normalized to Network Unicode format, as         |
   |                | described in Section 5.5. This string MUST NOT   |
   |                | be NULL terminated.                              |
   +----------------+--------------------------------------------------+

               Table 6: Software Inventory Attribute Fields

   The Software Inventory attribute contains some number of software
   inventory evidence records along with the core response attribute
   fields.  Given that the size of records can vary considerably, the
   length of this attribute is highly variable and, if transmitting a
   complete inventory, can be extremely large.  Enterprises might wish
   to constrain the use of Software Inventory attributes to targeted
   requests to avoid over-burdening the network unnecessarily.

   When copying a software inventory evidence record into the Record
   field, the record MUST be converted and normalized to use Network
   Unicode format prior to its inclusion in the record field.

5.11.  Software Events

   A SW-PC sends this attribute to a SW-PV to convey a list of events
   that include software inventory evidence records.  A SW-PV MUST NOT
   send this attribute.  The SW-PC either sends this attribute in
   fulfillment of an existing subscription where the establishing
   request has a Result Type of 0 and the Earliest EID is non-zero, or
   in direct response to a SW Request attribute where the Result Type is
   0 and the Earliest EID is non-zero.








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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Flags       |                  Event Count                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Request ID Copy / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           EID Epoch                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Last EID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Last Consulted EID                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               EID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timestamp                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Record Identifier                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Data Model Type PEN                 |Data Model Type|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Software Identifier Length      |  Software Locator Length    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Record Length                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Source Id Num |     Action    | Software Identifier (var len) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Software Locator (Variable Length)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Record (Variable Length)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 10: Software Events Attribute

   +----------------+--------------------------------------------------+
   | Field          | Description                                      |
   +----------------+--------------------------------------------------+
   | Flags: Bit 0 - | In the case that this attribute is sent in       |
   | Subscription   | fulfillment of a subscription this bit MUST be   |



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   | Fulfillment    | set (1).  In the case that this attribute is a   |
   |                | direct response to a SW Request, this bit MUST   |
   |                | be unset (0).                                    |
   |                |                                                  |
   | Flags: Bit 1-7 | Reserved for future use. This field MUST be set  |
   | - Reserved     | to zero on transmission and ignored upon         |
   |                | reception.                                       |
   |                |                                                  |
   | Event Count    | The number of events being reported in this      |
   |                | attribute. This field is a 3-byte unsigned       |
   |                | integer.  The EID, Timestamp, Record Identifier, |
   |                | Data Model Type PEN, Data Model Type, Software   |
   |                | Identifier Length, Software Locator Length,      |
   |                | Record Length, Source Identification Number,     |
   |                | Action, Software Identifier, Software Locator,   |
   |                | and Record fields are repeated, in order, the    |
   |                | number of times indicated in this field.  This   |
   |                | field value MAY be 0, in which case there are no |
   |                | instances of these fields.                       |
   |                |                                                  |
   | Request ID     | In the case where this attribute is in direct    |
   | Copy /         | response to a SW Request attribute from a SW-PV, |
   | Subscription   | this field MUST contain an exact copy of the     |
   | ID             | Request ID field from that SW Request.  In the   |
   |                | case where this attribute is sent in fulfillment |
   |                | of an active subscription, this field MUST       |
   |                | contain the Subscription ID of the subscription  |
   |                | being fulfilled by this attribute.               |
   |                |                                                  |
   | EID Epoch      | The EID Epoch of the Last EID value. This field  |
   |                | is an unsigned 4-byte integer.                   |
   |                |                                                  |
   | Last EID       | The EID of the last event recorded by the SW-PC, |
   |                | or 0 if the SW-PC has no recorded events. This   |
   |                | field contains the EID of the SW-PC's last       |
   |                | recorded change event (which might or might not  |
   |                | be included as an event record in this           |
   |                | attribute).                                      |
   |                |                                                  |
   | Last Consulted | The EID of the last event record that was        |
   | EID            | consulted when generating the event record list  |
   |                | included in this attribute. This is different    |
   |                | from the Last EID field value if and only if     |
   |                | this attribute is conveying a partial list of    |
   |                | event records. See Section 3.7.5 for more on     |
   |                | partial list of event records.                   |
   |                |                                                  |
   | EID            | The EID of the event in this event record.       |



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   |                |                                                  |
   | Timestamp      | The timestamp associated with the event in this  |
   |                | event record. This timestamp is the SW-PC's best |
   |                | understanding of when the given event occurred.  |
   |                | Note that this timestamp might be an estimate.   |
   |                | The Timestamp date and time MUST be represented  |
   |                | as an RFC 3339 [5] compliant ASCII string in     |
   |                | Coordinated Universal Time (UTC) time with the   |
   |                | additional restrictions that the 'T' delimiter   |
   |                | and the 'Z' suffix MUST be capitalized and       |
   |                | fractional seconds (time-secfrac) MUST NOT be    |
   |                | included. This field conforms to the date-time   |
   |                | ABNF production from section 5.6 of RFC 3339     |
   |                | [RFC3339] with the above restrictions.  Leap     |
   |                | seconds are permitted and SW-PVs MUST support    |
   |                | them.  The Timestamp string MUST NOT be NULL     |
   |                | terminated or padded in any way. The length of   |
   |                | this field is always 20 octets.                  |
   |                |                                                  |
   | Record         | A 4-byte, unsigned integer containing the Record |
   | Identifier     | Identifier value from a software inventory       |
   |                | evidence record.                                 |
   |                |                                                  |
   | Data Model     | A 3-byte unsigned integer containing the Private |
   | Type PEN       | Enterprise Number (PEN) of the organization that |
   |                | assigned the meaning of the Data Model Type      |
   |                | value.                                           |
   |                |                                                  |
   | Data Model     | A 1-byte unsigned integer containing an          |
   | Type           | identifier number that identifies the data model |
   |                | of the reported record.                          |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Identifier     | in bytes of the Software Identifier field.       |
   | Length         |                                                  |
   |                |                                                  |
   | Software       | A 2-byte unsigned integer indicating the length  |
   | Locator Length | in bytes of the Software Locator field.          |
   |                |                                                  |
   | Record Length  | This is a 4-byte unsigned integer indicating the |
   |                | length of the Record field in bytes.             |
   |                |                                                  |
   | Source         | The Source Identification Number associated with |
   | Identification | the source from which this software installation |
   | Number         | inventory instance was reported.                 |
   |                |                                                  |
   | Action         | The type of event that is recorded in this event |
   |                | record. Possible values are: 1 = CREATION - the  |



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   |                | addition of a record to the endpoint's Software  |
   |                | Inventory Evidence Collection; 2 = DELETION -    |
   |                | the removal of a record from the endpoint's      |
   |                | Software Inventory Evidence Collection; 3 =      |
   |                | ALTERATION - There was an alteration to a record |
   |                | within the endpoint's Software Inventory         |
   |                | Evidence Collection. All other values are        |
   |                | reserved for future use and MUST NOT be used     |
   |                | when sending attributes. In the case where a SW- |
   |                | PV receives an event record that uses an action  |
   |                | value other than the ones defined here, it MUST  |
   |                | ignore that event record but SHOULD process      |
   |                | other event records in this attribute as normal. |
   |                |                                                  |
   | Software       | A string containing the Software Identifier      |
   | Identifier     | value from a software inventory evidence record. |
   |                | This field value MUST be normalized to Network   |
   |                | Unicode format, as described in Section 5.5.     |
   |                | This string MUST NOT be NULL terminated.         |
   |                |                                                  |
   | Software       | A string containing the Software Locator value.  |
   | Locator        | This is expressed as a URI. This field value     |
   |                | MUST be normalized to Network Unicode format as  |
   |                | described in Section 3.4.4. This string MUST NOT |
   |                | be NULL terminated.                              |
   |                |                                                  |
   | Record         | A software inventory evidence record as a        |
   |                | string. The record MUST be converted and         |
   |                | normalized to Network Unicode format, as         |
   |                | described in Section 5.5. This string MUST NOT   |
   |                | be NULL terminated.                              |
   +----------------+--------------------------------------------------+

                 Table 7: Software Events Attribute Fields

   The fields of this attribute are used in the same way as the
   corresponding fields of the previous attributes.  As with the
   Software Inventory attribute, a Software Events attribute can be
   quite large if many events have occurred following the event
   indicated by a request's Earliest EID.  As such, it is recommended
   that the SW Request attributes only request full records be sent
   (Result Type set to 0) in a targeted request, thus constraining the
   response just to records that match a given set of Software
   Identifiers.

   As with the Software Identifier Events Attribute, this attribute MUST
   only contain event records with EIDs coming from the current EID
   Epoch of the SW-PC.



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   As with the Software Inventory Attribute, the SW-PC MUST perform
   conversion and normalization of the record.

5.12.  Subscription Status Request

   A SW-PV sends this attribute to a SW-PC to request a list of active
   subscriptions for which the requesting SW-PV is the subscriber.  A
   SW-PC MUST NOT send this attribute.

   This attribute has no fields.

   A SW-PC MUST respond to this attribute by sending a Subscription
   Status Response attribute (or a PA-TNC Error attribute if it is
   unable to correctly provide a response).

5.13.  Subscription Status Response

   A SW-PC sends this attribute to a SW-PV to report the list of active
   subscriptions for which the receiving SW-PV is the subscriber.  A SW-
   PV MUST NOT send this attribute.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Status Flags  |            Subscription Record Count          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Flags         |          Software Identifier Count            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Request ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Earliest EID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Software Identifier Length   | Software Identifier (var len) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 11: Subscription Status Response Attribute













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   +-----------------+-------------------------------------------------+
   | Field           | Description                                     |
   +-----------------+-------------------------------------------------+
   | Flags: Bit 0-7  | Reserved for future use. This field MUST be set |
   | - Reserved      | to zero on transmission and ignored upon        |
   |                 | reception.                                      |
   |                 |                                                 |
   | Subscription    | The number of subscription records that follow. |
   | Record Count    | This field is a 3-byte unsigned integer.  The   |
   |                 | Flags, Software Identifier Count, Request ID,   |
   |                 | Earliest EID, Software Identifier Length, and   |
   |                 | Software Identifier fields are repeated, in     |
   |                 | order, the number of times indicated in this    |
   |                 | field. This field value MAY be 0 in which case  |
   |                 | there are no instances of these fields.         |
   |                 |                                                 |
   | Flags, Software | For each active subscription, these fields      |
   | Identifier      | contain an exact copy of the fields with the    |
   | Count, Request  | same name as provided in the subscription's     |
   | ID, Earliest    | establishing request.                           |
   | EID, Software   |                                                 |
   | Identifier      |                                                 |
   | Length, and     |                                                 |
   | Software        |                                                 |
   | Identifier      |                                                 |
   +-----------------+-------------------------------------------------+

               Table 8: Subscription Status Response Fields

   A Subscription Status Response contains zero or more subscription
   records.  Specifically, it MUST contain one subscription record for
   each active subscription associated with the party that sent the
   Subscription Status Request to which this attribute is a response.
   As described in Section 3.8.2, the SW-PC MUST use the requester's
   Connection ID and its Posture Validator ID to determine which
   subscriptions are associated with the requester.

   A SW-PC MUST send a Subscription Status Response attribute in
   response to a Subscription Status Request attribute.  The only
   exception to this is if the SW-PC experiences an error condition that
   prevents it from correctly populating the Subscription Status
   Response attribute, in which case it MUST respond with a PA-TNC Error
   attribute appropriate to the type of error experienced.  If there are
   no active subscriptions associated with the requesting party, the
   Subscription Status Response attribute will consist of its Status
   Flags field, a Subscription Record Count field with a value of 0, and
   no additional fields.




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   Each subscription record included in a Subscription Status Response
   attribute duplicates the fields of a SW Request attribute that was
   the establishing request of a subscription.  Note that the Request ID
   field in the record captures the Subscription ID associated with the
   given subscription record (since the Subscription ID is the same as
   the Request ID of the establishing request).  Note also that if the
   establishing request is targeted, then its Record Count field will be
   non-zero and, within that subscription record, the Software
   Identifier Length and Software Identifier fields are repeated, in
   order, the number of times indicated in the Record Count field.  As
   such, each subscription record can be different sizes.  If the
   establishing request is not targeted (Record Count field is 0), the
   subscription record has no Software Identifier Length or Software
   Identifier fields.

   When a SW-PV compares the information received in a Subscription
   Status Response to its own records of active subscriptions it should
   be aware that the SW-PC might be unable to distinguish this SW-PV
   from other SW-PVs on the same NEA Server.  As a result, it is
   possible that the SW-PC will report more subscription records than
   the SW-PV recognizes.  For this reason, SW-PVs SHOULD NOT
   automatically assume that extra subscriptions reported in a
   Subscription Status Response indicate a problem.

5.14.  Source Metadata Request

   A SW-PV sends this attribute to a SW-PC to request metadata about
   sources that the SW-PC is using to collect software inventory
   information.  A SW-PC MUST NOT send this attribute.

   This attribute has no fields.

   A SW-PC MUST respond to this attribute by sending a Sources Metadata
   Response attribute (or a PA-TNC Error attribute if it is unable to
   correctly provide a response).

5.15.  Source Metadata Response

   A SW-PC sends this attribute to a SW-PV to provide descriptive
   metadata about the sources of software inventory information used by
   the SW-PC.  A SW-PV MUST NOT send this attribute.










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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            | Source Count  | Source ID     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Metadata Length         |  Metadata (variable length)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Source Metadata Response Attribute

   +----------+--------------------------------------------------------+
   | Field    | Description                                            |
   +----------+--------------------------------------------------------+
   | Reserved | Reserved for future use. This field MUST be set to     |
   |          | zero on transmission and ignored upon reception.       |
   |          |                                                        |
   | Source   | The number of source records that follow. The Source   |
   | Count    | ID, Metadata Size, and Metadata fields are repeated,   |
   |          | in order, the number of times indicated by this field. |
   |          | This field MAY be 0, in which case no fields follow    |
   |          | (but this would only be done to indicate that the SW-  |
   |          | PC has no active sources, which would not be a usual   |
   |          | situation).                                            |
   |          |                                                        |
   | Source   | The Source ID number associated with the described     |
   | ID       | source for any communications with the recipient SW-   |
   |          | PV.                                                    |
   |          |                                                        |
   | Metadata | A 2-byte unsigned integer indicating the length in     |
   | Length   | bytes of the Metadata field.                           |
   |          |                                                        |
   | Metadata | A string containing descriptive metadata about the     |
   |          | indicated data source. This string MUST NOT be NULL    |
   |          | terminated.                                            |
   +----------+--------------------------------------------------------+

                      Source Metadata Response Fields

   A Source Metadata Response attribute contains 0 or more records, each
   describing one of the data sources the SW-PC uses to collect software
   inventory information.  It SHOULD contain one metadata record for
   each source that the SW-PC uses.  (There might be reasons not to
   inform certain SW-PVs of the presence of certain data sources.)  The
   attribute MUST contain a metadata record for each source that has
   been identified in inventory or event messages to the given SW-PV.





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   A SW-PC MUST send a Source Metadata Response attribute in response to
   a Source Metadata Request attribute.  The only exception to this is
   if the SW-PC experiences an error condition that prevents it from
   correctly populating the Source Metadata Response attribute, in which
   case it MUST respond with a PA-TNC Error attribute appropriate to the
   type of error experienced.

   The Source Count field indicates how many source metadata records are
   included in the attribute.  Each included record consists of a Source
   Identifier, Metadata Length, and Metadata field.

   The Source Identifier corresponds to the Source Identifier field in
   inventory and event messages.  In the case where the Source
   Identifier value in a Source Metadata Response attribute matches a
   Source Identifier associated with an event or inventory record and
   both the Source Metadata Response and the inventory/event record were
   sent to the same SW-PV, the source described in the Metadata field
   MUST be the same source that provided the event or inventory record
   associated with the Source Identifier.  Recall that a SW-PC MAY use
   different Source Identifier associations with different SW-PVs.  When
   sending to a giving SW-PV, the SW-PC MUST use the recipient SW-PVs
   Source Identifier associations.

   The Metadata Length indicates the length, in bytes, if the Metadata
   field.  The Metadata field contains information about the indicated
   data source.  This specification does not dictate a format for the
   contents of the Metadata field.  This field MAY include machine-
   readable information.  For broadest utility, the Metadata field
   SHOULD include human-readable, descriptive information about the data
   source.

5.16.  PA-TNC Error as Used by Software Inventory Message and Attributes
       for PA-TNC

   The PA-TNC Error attribute is defined in the PA-TNC specification
   [RFC5792], and its use here conforms to that specification.  A PA-TNC
   Error can be sent due to any error in the PA-TNC exchange and might
   also be sent in response to error conditions specific to the Software
   Inventory Message and Attributes for PA-TNC exchange.  The latter
   case utilizes error codes defined below.

   A PA-TNC Error MUST be sent by a SW-PC in response to a SW Request in
   the case where the SW-PC encounters a fatal error (i.e., an error
   that prevents further processing of an exchange) relating to the
   attribute exchange.  A SW-PV MUST NOT send this attribute.  In the
   case where the SW-PV experiences a fatal error, it MUST handle the
   error without sending a PA-TNC Error attribute.  The SW-PV MAY take




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   other actions in response to the error, such as logging the cause of
   the error, or even taking actions to isolate the endpoint.

   A PA-TNC Error attribute is sent instead of a SW Response attribute
   due to factors that prevent the reliable creation of a SW Response.
   As such, a SW-PC MUST NOT send both a PA-TNC Error attribute and a SW
   Response attribute in response to a single SW Request attribute.

   Table 9 lists the Error Code values for the PA-TNC Error attribute
   specific to the Software Inventory Message and Attributes for PA-TNC
   exchange.  Error codes are shown in both hexadecimal and decimal
   format.  In all of these cases, the Error Code Vendor ID field MUST
   be set to 0x000000, corresponding to the IETF SMI Private Enterprise
   Number.  The Error Information structures for each error type are
   described in the following subsections.

   Note that a message with a Software Inventory Message and Attributes
   for PA-TNC attribute might also result in an error condition covered
   by the Standard PA-TNC Error Codes defined in PA-TNC.  For example, a
   SW Attribute might have an invalid parameter, leading to an error
   code of "Invalid Parameter".  In this case, the SW-PC MUST use the
   appropriate PA-TNC Error Code value as defined in Section 4.2.8 of
   PA-TNC specification.

   +-----------------------+-------------------------------------------+
   | Error Code Value      | Description                               |
   +-----------------------+-------------------------------------------+
   | 0x00000020 (32)       | SW_ERROR. This indicates a fatal error    |
   |                       | (i.e., an error that precludes the        |
   |                       | creation of a suitable response           |
   |                       | attribute) other than the errors          |
   |                       | described below but still specific to the |
   |                       | processing of SW Attributes. The          |
   |                       | Description field SHOULD contain          |
   |                       | additional diagnostic information.        |
   |                       |                                           |
   | 0x00000021 (33)       | SW_SUBSCRIPTION_DENIED_ERROR. This        |
   |                       | indicates that the SW-PC denied the SW-   |
   |                       | PV's request to establish a subscription. |
   |                       | The Description field SHOULD contain      |
   |                       | additional diagnostic information.        |
   |                       |                                           |
   | 0x00000022 (34)       | SW_RESPONSE_TOO_LARGE_ERROR. This         |
   |                       | indicates that the SW-PC's response to    |
   |                       | the SW-PV's request was too large to be   |
   |                       | serviced. The error information structure |
   |                       | indicates the largest possible size of a  |
   |                       | response supported by the SW-PC (see      |



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   |                       | Section 5.16.2).  The Description field   |
   |                       | SHOULD contain additional diagnostic      |
   |                       | information.                              |
   |                       |                                           |
   | 0x00000023 (35)       | SW_SUBSCRIPTION_FULFILLMENT_ERROR. This   |
   |                       | indicates that the SW-PC experienced an   |
   |                       | error fulfilling a given subscription.    |
   |                       | The error information includes the        |
   |                       | Subscription ID of the relevant           |
   |                       | subscription, as well as a sub-error that |
   |                       | describes the nature of the error the SW- |
   |                       | PC experienced. The SW-PC and SW-PV MUST  |
   |                       | treat the identified subscription as      |
   |                       | cancelled.                                |
   |                       |                                           |
   | 0x00000024 (36)       | SW_SUBSCRIPTION_ID_REUSE_ERROR. This      |
   |                       | indicates that the SW-PC received a SW    |
   |                       | Request from a given SW-PV where the      |
   |                       | Request ID of that SW Request is          |
   |                       | currently used as the Subscription ID of  |
   |                       | an active subscription with that SW-PV.   |
   |                       | This error does not cancel the identified |
   |                       | subscription.                             |
   |                       |                                           |
   | 0x00000025-0x0000002F | RESERVED. These Error Codes are reserved  |
   | (37-47)               | for use by future revisions of the        |
   |                       | Software Inventory Message and Attributes |
   |                       | for PA-TNC specification. Any PA-TNC      |
   |                       | Error attribute using one of these Error  |
   |                       | Codes MUST be treated as indicating a     |
   |                       | fatal error on the sender without further |
   |                       | interpretation.                           |
   +-----------------------+-------------------------------------------+

      Table 9: PA-TNC Error Codes for Software Inventory Message and
                           Attributes for PA-TNC

   The following subsections describe the structures present in the
   Error Information fields.

5.16.1.  SW_ERROR, SW_SUBSCRIPTION_DENIED_ERROR and
         SW_SUBSCRIPTION_ID_REUSE_ERROR Information

   The SW_ERROR error code indicates that the sender (the SW-PC) has
   encountered an error related to the processing of a SW Request
   attribute but which is not covered by more specific SW error codes.
   The SW_SUBSCRIPTION_DENIED_ERROR is used when the SW-PV requests to
   establish a subscription or clear all subscriptions from the given



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   SW-PV, but the SW-PC is unable or unwilling to comply with this
   request.  The SW_SUBSCRIPTION_ID_REUSE_ERROR is used when the SW-PC
   receives a SW Request whose Request ID duplicates a Subscription ID
   of an active subscription with the request's sender.  All of these
   error codes use the following error information structure.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Copy of Request ID / Subscription ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Description (variable length)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 12: SW Error, Subscription Error, and Subscription ID Reuse
                                Information

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Copy of      | In the case that this error condition is generated |
   | Request ID / | in direct response to a SW Request attribute, this |
   | Subscription | field MUST contain an exact copy of the Request ID |
   | ID           | field in the SW Request attribute that caused this |
   |              | error.  In the case that the attribute in question |
   |              | is generated in fulfillment of an active           |
   |              | subscription, this field MUST contain the          |
   |              | Subscription ID of the subscription for which the  |
   |              | attribute was generated.  (This is only possible   |
   |              | if the error code is SW_ERROR as the other errors  |
   |              | are not generated by subscription fulfillment.)    |
   |              | Note that, in this case, the indicated error       |
   |              | appears as a sub-error for a                       |
   |              | SW_SUBSCRIPTION_FULFILLMENT_ERROR, as described in |
   |              | Section 5.16.3.                                    |
   |              |                                                    |
   | Description  | A UTF-8 string describing the condition that       |
   |              | caused this error. This field MAY be 0-length.     |
   |              | However, senders SHOULD include some description   |
   |              | in all PA-TNC Error attributes of these types.     |
   |              | This field MUST NOT be NULL terminated.            |
   +--------------+----------------------------------------------------+

     Table 10: SW Error, Subscription Error, and Subscription ID Reuse
                            Information Fields




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   This error information structure is used with SW_ERROR,
   SW_SUBSCRIPTION_DENIED_ERROR, and SW_SUBSCRIPTION_ID_REUSE_ERROR
   status codes to identify the SW Request attribute that precipitated
   the error condition and to describe the error.  The Description field
   contains text describing the error.  The SW-PC MAY encode machine-
   interpretable information in this field, but SHOULD also include a
   human-readable description of the error, since the receiving SW-PV
   might not recognize the SW-PC's encoded information.

5.16.2.  SW_RESPONSE_TOO_LARGE_ERROR Information

   The SW_RESPONSE_TOO_LARGE_ERROR error code indicates that a response
   generated by a SW-PC in response to a SW-PV's SW Request attribute
   was too large to send.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Copy of Request ID / Subscription I              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Maximum Allowed Size                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Description (variable length)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


            Figure 13: SW Response Too Large Error Information























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   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Copy of      | In the case that the attribute in question is      |
   | Request ID / | generated in direct response to a SW Request, this |
   | Subscription | field MUST contain an exact copy of the Request ID |
   | ID           | field in the SW Request attribute that caused this |
   |              | error.  In the case that the attribute in question |
   |              | is generated in fulfillment of an active           |
   |              | subscription, this field MUST contain the          |
   |              | Subscription ID of the subscription for which the  |
   |              | attribute was generated. Note that, in the latter  |
   |              | case, the SW_RESPONSE_TOO_LARGE_ERROR appears as a |
   |              | sub-error for a SW_SUBSCRIPTION_FULFILLMENT_ERROR, |
   |              | as described in Section 5.16.3.                    |
   |              |                                                    |
   | Maximum      | This field MUST contain an unsigned integer        |
   | Allowed Size | indicating the largest permissible size, in bytes, |
   |              | of SW Attribute that the SW-PC is currently        |
   |              | willing to send in response to a SW Request        |
   |              | attribute.                                         |
   |              |                                                    |
   | Description  | A UTF-8 string describing the condition that       |
   |              | caused this error. This field MAY be 0-length.     |
   |              | However, senders SHOULD include some description   |
   |              | in all PA-TNC Error attributes of these types.     |
   |              | This field MUST NOT be NULL terminated.            |
   +--------------+----------------------------------------------------+

         Table 11: SW Response Too Large Error Information Fields

   This error structure is used with the SW_RESPONSE_TOO_LARGE_ERROR
   status code to identify the SW Request attribute that precipitated
   the error condition and to describe the error.  The Maximum Allowed
   Size field indicates the largest attribute the SW-PC is willing to
   send in response to a SW Request under the current circumstances.
   Note that under other circumstances, the SW-PC might be willing to
   return larger or smaller responses than indicated (such as if the
   endpoint connects to the NEA Server using a different network
   protocol).  The other fields in this error information structure have
   the same meanings as corresponding fields in the SW_ERROR and
   SW_SUBSCRIPTION_DENIED_ERROR information structure.

5.16.3.  SW_SUBSCRIPTION_FULFILLMENT_ERROR Information

   The SW_SUBSCRIPTION_FULFILLMENT_ERROR error code indicates that the
   SW-PC encountered an error while fulfilling a subscription.  The
   bytes after the first 4 octets duplicate a PA-TNC Error attribute (as



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   described in Section 4.2.8 of PA-TNC) that is used to identify the
   nature of the encountered error.


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Subscription ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |           Sub Error Code Vendor ID            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Sub Error Code                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Sub Error Information (Variable Length)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


         Figure 14: SW Subscription Fulfillment Error Information

   +--------------+----------------------------------------------------+
   | Field        | Description                                        |
   +--------------+----------------------------------------------------+
   | Subscription | This field MUST contain the Subscription ID of the |
   | ID           | subscription whose fulfillment caused this error.  |
   |              |                                                    |
   | Reserved     | This field MUST contain the value of the Reserved  |
   |              | field of a PA-TNC Error attribute that describes   |
   |              | the error condition encountered during             |
   |              | subscription processing.                           |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Code Vendor  | Code Vendor ID field of a PA-TNC Error attribute   |
   | ID           | that describes the error condition encountered     |
   |              | during subscription processing.                    |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Code         | Code field of a PA-TNC Error attribute that        |
   |              | describes the error condition encountered during   |
   |              | subscription processing.                           |
   |              |                                                    |
   | Sub Error    | This field MUST contain the value of the Error     |
   | Information  | Information field of a PA-TNC Error attribute that |
   |              | describes the error condition encountered during   |
   |              | subscription processing.                           |
   +--------------+----------------------------------------------------+

      Table 12: SW Subscription Fulfillment Error Information Fields




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   This error structure is used with the
   SW_SUBSCRIPTION_FULFILLMENT_ERROR status code.  The first 4 octets of
   this error structure contain the Subscription ID of the subscription
   that was being fulfilled when the error occurred.  The remaining
   fields of this error structure duplicate the fields of a PA-TNC Error
   attribute, referred to as the "sub-error".  The error code of the
   sub-error corresponds to the type of error that the SW-PC encountered
   while fulfilling the given subscription.  The sub-error MUST NOT have
   an error code of SW_SUBSCRIPTION_FULFILLMENT_ERROR.

   The SW-PC sending a PA-TNC Error attribute with this error code, and
   the SW-PV receiving it, MUST treat the subscription identified by the
   Subscription ID field as cancelled.  All other subscriptions are
   unaffected.

6.  Supported Data Models

   Software Inventory Message and Attributes for PA-TNC supports an
   extensible list of data models for representing and transmitting
   software inventory information.  This list of data models appears in
   the Software Data Model IANA registry (see Section 10.4).  This
   document provides guidance for an initial set of data models.  Other
   documents might provide guidance on the use of new data models by
   Software Inventory Message and Attributes for PA-TNC, and will be
   referenced by extensions to the Software Data Model IANA registry.

6.1.  ISO 2015 SWID Tags using XML

   The International Organization for Standardization and the
   International Electrotechnical Commission (ISO/IEC) published the
   specification governing SWID tag construction and use in 2009 with a
   revised version published in 2015.  [SWID15] Since that time, a
   growing number of vendors have integrated SWID tags into their
   software products.  Doing so significantly simplifies the task of
   identifying these pieces of software: instead of relying on discovery
   processes that look for clues as to software presence, such as the
   presence of particular files or registry keys.  A readily available
   list of SWID tags provides simple and immediate evidence as to the
   presence of the given piece of software.

   SWID Message and Attributes for PA-TNC has no reliance on the
   presence or management of SWID tags on an endpoint as described in
   the ISO specification.  However, the data model for describing
   software that is presented in the ISO specification provides a robust
   and comprehensive way of describing software and is adopted here as a
   means of representing and transmitting software information.  It
   should be emphasized, the use of the ISO SWID tag data model makes no
   assumption as to whether the source of the recorded information was,



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   in fact, an ISO SWID tag harvested from the endpoint or whether the
   information was created using some other source and normalized to the
   SWID format.

6.1.1.  Guidance on Normalizing Source Data to ISO 2015 SWID Tags using
        XML

   Any record associated with this Software Data Model Type MUST conform
   to the ISO/IEC 19770-2-2015 [SWID15] specification.  Any such tag
   SHOULD use a UTF-8 encoding, but MUST NOT alter the existing encoding
   if doing so would invalidate digital signatures included in the tag.

   If generating a new ISO 2015 SWID tag, the software generating the
   tag MUST use a Tag Creator RegID that is associated with the
   generating software, unless this is impossible, in which case it MUST
   use the "http://invalid.unavailable" Tag Creator RegID value.  Do not
   use a RegID associated with any other party.  In particular, it is
   incorrect to use a Tag Creator RegID associated with the software
   being described by the tag, the enterprise that is using the
   software, or any other entity except that of the party that built the
   tool that is generating the SWID tag.  This reflects the requirement
   that the Tag Creator RegID identify the party that created the tag.

6.1.2.  Guidance on Creation of Software Identifiers from ISO 2015 SWID
        Tags

   A Software Identifier generated from an ISO 2015 SWID tag is
   expressed as a concatenation of the value of the Tag Creator RegID
   field and the Unique ID field.  Specifically, it MUST be of the form:
   NUMBER "::" TAG_CREATOR_REGID UNIQUE_ID, where NUMBER is the length
   of TAG_CREATOR_REGID in bytes.  The rest of the Software Identifier
   MUST be the concatenation of the Tag Creator RegID and the Unique ID
   from the tag, without any connecting character or whitespace.

6.2.  ISO 2009 SWID Tags using XML

   As noted above, ISO's SWID tag specification provides a useful data
   model for representation of software information.  As of the writing
   of this specification, while the 2015 specification is considered
   more comprehensive and addresses some issues with the 2009
   specification, 2009-format SWID tags remain far more common in
   deployments.  For this reason, ISO 2009 SWID tags are included in the
   Software Data Model IANA table.








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6.2.1.  Guidance on Normalizing Source Data to ISO 2009 SWID Tags using
        XML

   Any record associated with this Software Data Model Type MUST conform
   to the ISO/IEC 19770-2-2009 [SWID09] specification.  Any such tag
   SHOULD use a UTF-8 encoding, but MUST NOT alter the existing encoding
   if doing so would invalidate digital signatures included in the tag.

   If generating a new ISO 2009 SWID tag, the software generating the
   tag MUST use a Tag Creator RegID that is associated with the
   generating software unless this is impossible, in which case it MUST
   use "http://invalid.unavailable", which indicates the Tag Creator is
   unknown.  Do not use a RegID associated with any other party.  In
   particular, it is incorrect to use a Tag Creator RegID associated
   with the software being described by the tag, the enterprise that is
   using the software, or any other entity except that of the party that
   built the tool that is generating the SWID tag.  This reflects the
   requirement that the Tag Creator RegID identify the party that
   created the tag.

6.2.2.  Guidance on Creation of Software Identifiers from ISO 2009 SWID
        Tags

   A Software Identifier generated from an ISO 2009 SWID tag is
   expressed as a concatenation of the value of the Tag Creator RegID
   field and the Unique ID field.  Specifically, it MUST be of the form:
   NUMBER "::" TAG_CREATOR_REGID UNIQUE_ID, where NUMBER is the length
   of TAG_CREATOR_REGID in bytes.  The rest of the Software Identifier
   MUST be the concatenation of the Tag Creator RegID and the Unique ID
   from the tag, without any connecting character or whitespace.

7.  Security Considerations

   This section discusses some of the security threats facing Posture
   Collectors and Posture Validators that implement the Software
   Inventory Message and Attributes for PA-TNC protocol.  This section
   primarily notes potential issues for implementers to consider,
   although it does contain a handful of normative requirements to
   address certain security issues.  The issues identified below focus
   on capabilities specific to this document.  Implementers are advised
   to consult other relevant NEA specifications, particularly [RFC5209]
   (the NEA Architecture) and [RFC5792] (PA-TNC), for security issues
   that are applicable to such components in general.








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7.1.  Evidentiary Value of Software Inventory Evidence Records

   The degree to which an endpoint's Software Inventory Evidence
   Collection accurately reflects the endpoint's actual software load
   and any changes made to this software load is dependent on the
   accuracy of the tools used to populate and manage the software
   inventory evidence records in this collection.  Some tools might not
   be designed to update records in the Software Inventory Evidence
   Collection in real time, resulting in a collection that is out-of-
   sync with actual system state.  Moreover, tools might inaccurately
   characterize software, or fail to properly record its removal.
   Finally, it is likely that there will be software on the endpoint
   that is not tracked by any source and thus is not reflected in the
   Software Inventory Evidence Collection.  Users of collected software
   inventory evidence records need to understand that the information
   provided by the Software Inventory Message and Attributes for PA-TNC
   capability cannot be treated as completely accurate.  Nonetheless,
   having endpoints report this information can still provide useful
   insights into the state of the endpoint's software load, and can
   alert administrators and policy tools of situations that require
   remediation.

7.2.  Sensitivity of Collected Records

   Software records on an endpoint are generally not considered to be
   sensitive, although there can be exceptions to this generalization as
   noted in the section on Privacy Considerations.  In general, an
   endpoint's Software Inventory Evidence Collection can be browsed and
   individual records read by any party with access to the endpoint.
   This is generally not considered to be problematic, as those with
   access to the endpoint can usually learn of everything disclosed by
   that endpoint's records simply by inspecting other parts of the
   endpoint.

   The situation changes when an endpoint's inventory records are
   collected and stored off of the endpoint itself, such as on a NEA
   Server or CMDB.  Inventory records represent a wealth of information
   about the endpoint in question and, for an adversary who does not
   already have access to the endpoint, a collection of the endpoint's
   inventory records might provide many details that are useful for
   mounting an attack.  A list of the inventory records associated with
   an endpoint reveals a list of software installed on the endpoint.
   This list can be very detailed, noting specific versions and even
   patch levels, which an adversary can use to identify vulnerable
   software and design efficacious attacks.

   In addition, other information might also be gleaned from a
   collection of software inventory records:



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   o  An inventory record might include information about where the
      product was installed on a given endpoint.  This can reveal
      details about the file organization of that endpoint that an
      attacker can utilize.

   o  An inventory record might include information about how the
      software was provided to the endpoint, who in an organization
      signs off on the package release, and who packaged the product for
      installation.  This information might be used as a starting point
      for the development of supply chain attacks.

   o  Events affecting inventory records are reported with timestamps
      indicating when each given event occurred.  This can give the
      attacker an indication of how quickly an organization distributes
      patches and updates, helping the attacker determine how long an
      attack window might remain open.

   Any consolidated software inventory is a potential risk, because such
   an inventory can provide an adversary an insight into the
   enterprise's configuration and management process.  It is recommended
   that a centralized software inventory record collection be protected
   against unauthorized access.  Mechanisms to accomplish this can
   include encrypting the data at rest, ensuring that access to the data
   is limited only to authorized individuals and processes, and other
   basic security precautions.

7.3.  Integrity of Endpoint Records

   SW-PCs maintain records of detected changes to the endpoint's
   Software Inventory Evidence Collection.  These records are used to
   respond to a SW-PV's request for change events.  The SW-PV might use
   a list of reported events to update its understanding of the
   endpoint's Software Inventory Evidence Collection without needing to
   receive a full inventory report from the SW-PC.  For this reason,
   preserving the integrity of the SW-PC's record of events is extremely
   important.  If an attacker modifies the SW-PC's record of changes to
   the endpoint's Software Inventory Evidence Collection, this might
   cause the SW-PV's understanding of the endpoint's Software Inventory
   Evidence Collection to differ from its actual state.  Results might
   include leading the SW-PV to believe that absent software was
   present, that present software was absent, that patches have been
   installed even if this is not the case, or to be unaware of other
   changes to Software Inventory Evidence Records.  As such, the SW-PC
   MUST take steps to protect the integrity of its event records.

   In addition, records of established SW-PV subscriptions also require
   protection against manipulation or corruption.  If an attacker is
   able to modify or delete records of an established subscription by a



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   SW-PV, the SW-PC might fail to correctly fulfill this subscription.
   The SW-PV would not be aware that its subscription was not being
   correctly fulfilled unless it received additional information that
   indicated a discrepancy.  For example, the SW-PV might collect a full
   inventory and realize from this that certain events had not been
   correctly reported in accordance with an established subscription.
   For this reason, the SW-PC MUST protect the integrity of subscription
   records.

7.4.  SW-PC Access Permissions

   A SW-PC requires sufficient permissions to collect Software Inventory
   Evidence Records from all of its supported sources, as well as
   sufficient permissions to interact with the endpoint's Posture Broker
   Client.  With regard to the former, this might require permissions to
   read the contents of directories throughout the file system.
   Depending on the operating environment and other activities
   undertaken by a SW-PC (or software that incorporates a SW-PC as one
   of its capabilities) additional permissions might be required by the
   SW-PC software.  The SW-PC SHOULD NOT be granted permissions beyond
   what it needs in order to fulfill its duties.

7.5.  Sanitization of Record Fields

   Not all sources of software inventory evidence are necessarily
   tightly controlled.  For example, consider a source that gathers
   .swid files from the endpoint's file system.  Any party could create
   a new .swid file that could be collected and turned into a Software
   Inventory Evidence Record.  As a result, it is important that the
   contents of source information not be automatically trusted.  In
   particular, tools that read source information and the Software
   Inventory Evidence Records derived therefrom, including SW-PCs, need
   to be careful to sanitize input to prevent buffer overflow attacks,
   encoding attacks, and other weaknesses that might be exploited by an
   adversary who can control the contents of a record.

7.6.  PA-TNC Security Threats

   In addition to the aforementioned considerations the Software
   Inventory Message and Attributes for PA-TNC protocol is subject to
   the same security threats as other PA-TNC transactions, as noted in
   Section 5.2 of PA-TNC [RFC5792].  These include, but are not limited
   to, attribute theft, message fabrication, attribute modification,
   attribute replay, attribute insertion, and denial of service.
   Implementers are advised to consult the PA-TNC specification to
   better understand these security issues.





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8.  Privacy Considerations

   As noted in Section 7.2, if an adversary can gain an understanding of
   the software installed on an endpoint, they can utilize this to
   launch attacks and maintain footholds on this endpoint.  For this
   reason, the NEA Server needs to ensure adequate safeguards are in
   place to prevent exposure of collected inventory records.  For
   similar reasons, it is advisable that an endpoint only send records
   to a NEA Server that is authorized to receive this information and
   that can be trusted to safeguard this information after collection.

9.  Relationship to Other Specifications

   This specification makes frequent reference to and use of other
   specifications.  This section describes these relationships.

   This specification is expected to participate in a standard NEA
   architecture.  As such, it is expected to be used in conjunction with
   the other protocols used in a NEA exchange.  In particular, SW
   Attributes are conveyed over PB-TNC [RFC5793], which is in turn
   conveyed over some variant of PT (either PT-TLS [RFC6876] or PT-EAP
   [RFC7171]).  These protocols have an especially important role, as
   they are responsible for ensuring that attributes defined under this
   specification are delivered reliably, securely, and to the
   appropriate party.

   It is important to note that the Product Information, Numeric
   Version, and String Version attributes defined in the PA-TNC
   specification [RFC5792] are also meant to convey information about
   installed applications and the versions thereof.  As such, there is
   some conceptual overlap between those attributes and the intent of
   this specification.  However, PA-TNC was designed to respond to very
   specific queries about specific classes of products, while the
   Software Inventory Message and Attributes for PA-TNC specification is
   able to convey a broader query, resulting in a more comprehensive set
   of evidence regarding an endpoint's installed software.  As such,
   this specification provides important capabilities not present in the
   PA-TNC specification.

10.  IANA Considerations

   This section extends multiple existing IANA registries.
   Specifically, it extends the PA-TNC Attribute Types and PA-TNC Error
   Codes defined in the PA-TNC specification [RFC5792] and the PA-
   Subtypes registry defined in the PB-TNC specification [RFC5793] and
   extended in PA-TNC.  This specification only adds values to these
   registries and does not alter how these registries work or are




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   maintained.  Consult the appropriate specifications for details on
   the operations and maintenance of these registries.

10.1.  PA Subtypes

   The following is an extension to the PA Subtype registry [1] defined
   in section 7.2 of the PA-TNC specification [RFC5792].

   +-----+---------+------------+--------------------------------------+
   | PEN | Integer | Name       | Defining Specification               |
   +-----+---------+------------+--------------------------------------+
   | 0   | 9       | SW         | Software Inventory Message and       |
   |     |         | Attributes | Attributes for PA-TNC                |
   +-----+---------+------------+--------------------------------------+

10.2.  Registry for PA-TNC Attribute Types

   Section 5.4 of this specification defines several new PA-TNC
   attributes.  The following values are added to the registry for PA-
   TNC Attribute Types defined in the PA-TNC specification.  Note that
   Table 2 in Section 5.4 lists these attributes but uses a hexadecimal
   value to identify their associated integer.  The integer values given
   in that table are identical to those provided here.  Note also that
   Table 2 includes an entry for PA-TNC Error attributes, but the IANA
   information associated with that attribute is already defined in the
   PA-TNC specification and is not reproduced here.

























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   +-----+---------+-------------------+-------------------------------+
   | PEN | Integer | Name              | Defining Specification        |
   +-----+---------+-------------------+-------------------------------+
   | 0   | 17      | SW Request        | Software Inventory Message    |
   |     |         |                   | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 18      | Software          | Software Inventory Message    |
   |     |         | Identifier        | and Attributes for PA-TNC     |
   |     |         | Inventory         |                               |
   |     |         |                   |                               |
   | 0   | 19      | Software          | Software Inventory Message    |
   |     |         | Identifier Events | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 20      | Software          | Software Inventory Message    |
   |     |         | Inventory         | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 21      | Software Events   | Software Inventory Message    |
   |     |         |                   | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 22      | Subscription      | Software Inventory Message    |
   |     |         | Status Request    | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 23      | Subscription      | Software Inventory Message    |
   |     |         | Status Response   | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 24      | Subscription      | Software Inventory Message    |
   |     |         | Status Response   | and Attributes for PA-TNC     |
   |     |         |                   |                               |
   | 0   | 25 - 31 | Reserved for      | Software Inventory Message    |
   |     |         | future use        | and Attributes for PA-TNC     |
   +-----+---------+-------------------+-------------------------------+

10.3.  Registry for PA-TNC Error Codes

   Section 5.16 of this specification defines several new PA-TNC Error
   Codes.  The following values are added to the registry for PA-TNC
   Error Codes defined in the PA-TNC specification.  Note that Table 9
   in Section 5.16 lists these codes but uses a hexadecimal value to
   identify their associated integer.  The integer values given in that
   table are identical to those provided here.











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   +-----+---------+-----------------------------------+---------------+
   | PEN | Integer | Name                              | Defining      |
   |     |         |                                   | Specification |
   +-----+---------+-----------------------------------+---------------+
   | 0   | 32      | SW_ERROR                          | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 33      | SW_SUBSCRIPTION_DENIED_ERROR      | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 34      | SW_RESPONSE_TOO_LARGE_ERROR       | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 35      | SW_SUBSCRIPTION_FULFILLMENT_ERROR | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 36      | SW_SUBSCRIPTION_ID_REUSE_ERROR    | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   |     |         |                                   |               |
   | 0   | 37-47   | Reserved for future use           | Software      |
   |     |         |                                   | Inventory     |
   |     |         |                                   | Message and   |
   |     |         |                                   | Attributes    |
   |     |         |                                   | for PA-TNC    |
   +-----+---------+-----------------------------------+---------------+

10.4.  Registry for Software Data Models

   The name for this registry is "Software Data Model Types".  Each
   entry in this registry should include a human readable name, an SMI
   Private Enterprise Number, a decimal integer value between 1 and
   2^8-1 (inclusive), and a reference to the specification where the use
   of this data model is defined.  This specification needs to provide



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   both a description of the format used by the data model and the
   procedures by which Software Identifiers are derived from a record
   expressed using this data model.  Note that a specification that just
   defines the data model structure and its use is generally not
   sufficient as it would likely lack the procedures for constructing a
   Software Identifier.  This is why the table below references the
   current specification for ISO SWID tags, rather than using the actual
   ISO SWID tag specification.

   The following entries for this registry are defined in this document.
   They are the initial entries in the registry for Software Data Model
   Types.  Additional entries to this registry are added by Expert
   Review with Specification Required, following the guidelines in
   [RFC5226].

   +-----+---------+----------------------------+----------------------+
   | PEN | Integer | Name                       | Defining             |
   |     |         |                            | Specification        |
   +-----+---------+----------------------------+----------------------+
   | 0   | 1       | ISO 2015 SWID Tags using   | **CURRENT            |
   |     |         | XML                        | SPECIFICATION**      |
   |     |         |                            |                      |
   | 0   | 2       | ISO 2009 SWID Tags using   | **CURRENT            |
   |     |         | XML                        | SPECIFICATION**      |
   |     |         |                            |                      |
   | 0   | 192-255 | Reserved for local         | N/A                  |
   |     |         | enterprise use             |                      |
   +-----+---------+----------------------------+----------------------+

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.





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   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <http://www.rfc-editor.org/info/rfc5198>.

   [RFC5209]  Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
              Tardo, "Network Endpoint Assessment (NEA): Overview and
              Requirements", RFC 5209, DOI 10.17487/RFC5209, June 2008,
              <http://www.rfc-editor.org/info/rfc5209>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5792]  Sangster, P. and K. Narayan, "PA-TNC: A Posture Attribute
              (PA) Protocol Compatible with Trusted Network Connect
              (TNC)", RFC 5792, DOI 10.17487/RFC5792, March 2010,
              <http://www.rfc-editor.org/info/rfc5792>.

   [SWID09]   The International Organization for Standardization/
              International Electrotechnical Commission, "Information
              Technology - Software Asset Management - Part 2: Software
              Identification Tag, ISO/IEC 19770-2", November 2009.

   [SWID15]   The International Organization for Standardization/
              International Electrotechnical Commission, "Information
              Technology - Software Asset Management - Part 2: Software
              Identification Tag, ISO/IEC 19770-2", October 2015.

11.2.  Informative References

   [NIST-SWID]
              The National Institute of Standards and Technology and The
              MITRE Corporation, "Guidelines for the Creation of
              Interoperable Software Identification (SWID) Tags", August
              2013.

   [RFC5793]  Sahita, R., Hanna, S., Hurst, R., and K. Narayan, "PB-TNC:
              A Posture Broker (PB) Protocol Compatible with Trusted
              Network Connect (TNC)", RFC 5793, DOI 10.17487/RFC5793,
              March 2010, <http://www.rfc-editor.org/info/rfc5793>.

   [RFC6876]  Sangster, P., Cam-Winget, N., and J. Salowey, "A Posture
              Transport Protocol over TLS (PT-TLS)", RFC 6876,
              DOI 10.17487/RFC6876, February 2013,
              <http://www.rfc-editor.org/info/rfc6876>.





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   [RFC7171]  Cam-Winget, N. and P. Sangster, "PT-EAP: Posture Transport
              (PT) Protocol for Extensible Authentication Protocol (EAP)
              Tunnel Methods", RFC 7171, DOI 10.17487/RFC7171, May 2014,
              <http://www.rfc-editor.org/info/rfc7171>.

11.3.  URIs

   [1] https://www.iana.org/assignments/pb-tnc-parameters/pb-tnc-
       parameters.xhtml#pb-tnc-parameters-2

Authors' Addresses

   Charles Schmidt
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: cmschmidt@mitre.org


   Daniel Haynes
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: dhaynes@mitre.org


   Chris Coffin
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: ccoffin@mitre.org


   David Waltermire
   National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, Maryland
   USA

   Email: david.waltermire@nist.gov





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   Jessica Fitzgerald-McKay
   Department of Defense
   9800 Savage Road
   Ft. Meade, Maryland
   USA

   Email: jmfitz2@nsa.gov












































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