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Versions: (draft-sangster-nea-pt-tls) 00 01 02 03 04 05 06 07 08 RFC 6876

Network Working Group                                        P. Sangster
Internet Draft                                      Symantec Corporation
Intended status: Proposed Standard                         N. Cam-Winget
Expires: December 2012                                        J. Salowey
                                                           Cisco Systems
                                                          August 7, 2012



            PT-TLS: A TCP-based Posture Transport (PT) Protocol
                       draft-ietf-nea-pt-tls-07.txt


Abstract

   This document specifies PT-TLS, a TCP-based Posture Transport (PT)
   protocol.  The PT-TLS protocol carries the Network Endpoint
   Assessment (NEA) message exchange under the protection of a
   Transport Layer Security (TLS) secured tunnel.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on November 7, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.




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   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 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...................................................3
      1.1. Prerequisites.............................................4
      1.2. Message Diagram Conventions...............................4
      1.3. Conventions used in this document.........................4
      1.4. Compatibility with other Specifications...................4
   2. Design Considerations..........................................5
      2.1. Benefits of TCP/IP Connectivity...........................5
      2.2. Leveraging Proven TLS Security............................6
      2.3. TLV-Oriented Based Message Encapsulation..................6
      2.4. No Change to Base TLS Protocol............................6
   3. PT-TLS Protocol................................................7
      3.1. Initiating a PT-TLS Session...............................8
         3.1.1. Issues with Server Initiated PT-TLS Sessions.........8
         3.1.2. Establish or Re-Use Existing PT-TLS Session..........9
      3.2. TCP Port Usage............................................9
      3.3. Preventing MITM Attacks with Channel Bindings.............9
      3.4. PT-TLS Message Flow......................................10
         3.4.1. Assessment Triggers.................................10
         3.4.2. PT-TLS Message Exchange Phases......................10
            3.4.2.1. TLS Setup Phase................................11
            3.4.2.2. PT-TLS Negotiation Phase.......................13
            3.4.2.3. PT-TLS Data Transport Phase....................13
         3.4.3. TLS Requirements....................................14
      3.5. PT-TLS Message Format....................................15
      3.6. IETF Namespace PT-TLS Message Types......................17
      3.7. PT-TLS Version Negotiation...............................20
         3.7.1. Version Request Message.............................20
         3.7.2. Version Response Message............................21
      3.8. Client Authentication using SASL.........................22
         3.8.1. SASL Client Authentication Requirements.............23
         3.8.2. SASL in PT-TLS Overview.............................23
         3.8.3. SASL Authentication Flow............................24
         3.8.4. Aborting SASL Authentication........................24
         3.8.5. Linkages to SASL Framework..........................25


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            3.8.5.1. SASL Service Name..............................25
            3.8.5.2. SASL Authorization Identity....................25
            3.8.5.3. SASL Security Layer............................25
            3.8.5.4. Multiple Authentications.......................25
         3.8.6. SASL Channel Bindings...............................25
         3.8.7. SASL Mechanisms.....................................25
         3.8.8. SASL Mechanism Selection............................26
         3.8.9. SASL Authentication Data............................27
         3.8.10. SASL Result........................................27
      3.9. Error Message............................................29
   4. Security Considerations.......................................32
      4.1. Trust Relationships......................................32
         4.1.1. Posture Transport Client............................32
         4.1.2. Posture Transport Server............................33
      4.2. Security Threats and Countermeasures.....................35
         4.2.1. Message Theft.......................................35
         4.2.2. Message Fabrication.................................36
         4.2.3. Message Modification................................36
         4.2.4. Denial of Service...................................36
         4.2.5. NEA Asokan Attacks..................................37
         4.2.6. Trust Anchors.......................................38
   5. Privacy Considerations........................................38
   6. IANA Considerations...........................................38
      6.1. Designated Expert Guidelines.............................39
      6.2. Registry for PT-TLS Message Types........................40
      6.3. Registry for PT-TLS Error Codes..........................41
   7. Acknowledgments...............................................42
   8. References....................................................42
      8.1. Normative References.....................................42
      8.2. Informative References...................................43

1. Introduction

   This document specifies PT-TLS, a TCP-based Posture Transport (PT)
   protocol protected by a TLS channel.

   NEA protocols are intended to be used for pre-admission assessment
   of endpoints joining the network and to assess endpoints already
   present on the network.  In order to support both usage models, two
   different types (or bindings) of PT protocols are necessary to
   operate before and after the endpoint has an assigned IP address and
   other network layer information.  This specification focuses on the
   PT protocol used to assess endpoints already present on the network
   and thus is able to use TCP/IP based transport protocols.  NEA has
   defined another protocol called PT-EAP [PT-EAP] to address
   assessment prior to the endpoint having an assigned IP address.



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   The PT protocol in the NEA architecture [RFC5209] is responsible for
   transporting PB-TNC [RFC5793] batches (often containing PA-TNC
   [RFC5792] attributes) over the network between the Posture Transport
   Client component of the NEA Client and the Posture Transport Server
   component of the NEA Server.  The PT protocol also offers strong
   security protections to ensure the exchanged messages are protected
   from a variety of threats from hostile intermediaries.

1.1. Prerequisites

   This document does not define an architecture or reference model.
   Instead, it defines one binding of the PT protocol that works within
   the reference model described in the NEA Overview and Requirements
   specification.  The reader is assumed to be thoroughly familiar with
   the NEA Overview and Requirements specification.  The NEA working
   group compared the functionality described in this specification
   against the requirements in the NEA Overview and Requirements
   specification and found that each applicable requirement was
   addressed.

1.2. Message Diagram Conventions

   This specification defines the syntax of PT-TLS messages 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, traversing the diagram from top to bottom and then from
   left to right within each line (which represents a 32-bit quantity).
   Multi-byte fields representing numeric values must be sent in
   network (big endian) byte order.

   Descriptions of bit field (e.g. flag) values are described referring
   to the position of the bit within the field.  These bit positions
   are numbered from the most significant bit through the least
   significant bit so a one octet field with only bit 0 set has the
   value 0x80.

1.3. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   RFC 2119 [RFC2119].

1.4. Compatibility with other Specifications

   One of the goals of the NEA effort is to deliver a single set of
   endpoint assessment standards, agreed upon by all parties.  For this


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   reason, the authors understand that the Trusted Computing Group
   (TCG) will be replacing its existing posture transport protocols
   with new versions that are equivalent to and interoperable with the
   NEA specifications.

2. Design Considerations

   This section discusses some of the key design considerations for the
   PT protocol.  This document specifies the PT binding for use when
   performing an assessment or reassessment after the endpoint has been
   admitted to the network and is capable of using TCP/IP to
   communicate with the NEA Server.   If the endpoint does not yet have
   TCP/IP layer access to the NEA Server (and vice versa), the endpoint
   can use the PT-EAP (Posture Transport (PT) Protocol for EAP Tunnel
   Methods) protocol when performing an assessment.

   Because the endpoint has TCP/IP access to the NEA Server
   (potentially on a restricted portion of the network), the NEA Client
   and NEA Server have the ability to establish (or re-use) a reliable
   TCP/IP connection in order to perform the assessment.  The TCP/IP
   connection enables the assessment to occur over a relatively high
   performance, reliable channel capable of supporting multiple
   roundtrip message exchanges in full duplex manner.  These connection
   properties are very different from what is available when the
   endpoint is initially joining the network (e.g. during an 802.1X
   based assessment), therefore the design described in this
   specification follows a different path to maximize the benefits of
   the underlying TCP/IP connection.

2.1. Benefits of TCP/IP Connectivity

   The PT protocol is typically able to offer to the NEA Client and NEA
   Server significantly higher quality of service and flexibility of
   operation than PT-EAP (Posture Transport (PT) Protocol for EAP
   Tunnel Methods).  However, there may be some added risks when the
   endpoint is on the network prior to its initial assessment (if no
   admission time assessment had been performed).  Because of these
   risks, the combined use of an EAP-based assessment during admission
   followed by reassessment using TCP/IP may be appropriate in some
   environments.
   Some of the benefits to having a TCP/IP based transport during an
   assessment include:

   o  Full Duplex connectivity - used to support asynchronous
      initiation of posture exchanges within a single TLS connection
      (e.g. triggered by alerts of posture or policy changes)



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   o  High Bandwidth - potentially much higher bandwidth than other
      transports (e.g. EAP) allowing more in-band data (e.g.
      remediation, verbose posture information)

   o  Large Messages - ability to send very large PA messages without
      directly fragmenting them (underlying carrier protocol may
      introduce fragmentation)

   o  Bi-directional - NEA Client and NEA Server can initiate an
      assessment or reassessment

   o  Multiple Roundtrips - NEA Client and NEA Server can exchange
      numerous messages without fear of infrastructure timeouts.
      However, the entire exchange should be kept as brief as possible
      if the user has to wait for its completion.

2.2. Leveraging Proven TLS Security

   All PT protocol bindings must be capable of providing strong
   authentication, integrity and confidentiality protection for the PB-
   TNC batches.  Rather than define a new protocol over TCP/IP to
   provide adequate protection, this specification requires the use of
   Transport Layer Security [RFC5246] to secure the connection.  TLS
   was selected because it's a widely deployed protocol with parallel
   protections to a number of the EAP tunnel methods, and it meets all
   of the security requirements.

2.3. TLV-Oriented Based Message Encapsulation

   The design of the PT-TLS protocol is based upon the use of type-
   length-value (TLV) oriented protocol message that identifies the
   type of message, the message's length and a potentially variable
   length payload value.  The use of a TLV orientated encoding was
   chosen to match the Internet standard PA-TNC and PB-TNC protocols.
   Because the PA-TNC, PB-TNC and PT-TLS protocols are typically
   implemented inside the same process space, this allows a common set
   of message parsing code to be used. Similarly creation of debugging
   tools is simplified by the common encoding methodologies.  TLV-based
   encoding was used in each of the NEA protocols in part because it
   enables a very space efficient representation on the network and is
   simpler to parse than some other encodings to benefit lower powered
   (or battery constrained) devices.

2.4. No Change to Base TLS Protocol

   During the design of the PT-TLS protocol, several approaches were
   considered with different costs and benefits.  Several considered


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   approaches involved integrating the PT protocol into the TLS
   handshake protocol.  Because the PT protocol requires the underlying
   TLS carrier to provide security protections, the PT protocol
   couldn't operate before the cipher suites were negotiated and in
   use.  One option was to integrate into the TLS handshake protocol
   after the ChangeCipherSpec phase allowing the PT message to be
   protected.  The benefit of this approach is that the assessment
   protocol could operate below the application protocols allowing for
   easier integration into applications.  However, making this change
   would require some extensions to the TLS handshake protocol
   standards and existing widely deployed TLS implementations, so it
   wasn't clear that the cost was warranted, particularly because the
   application independence can also be offered by a shim library
   between the application and TLS library that provides the PT
   protocol encapsulation/decapsulation.

   The other general approach considered was to have PT-TLS layer on
   top of TLS as an application protocol (using the standard
   application_data ContentType).  This has the advantage that existing
   TLS software could be used.  However, the PB-TNC traffic would need
   to be encapsulated/decapsulated by a new PT-TLS protocol layer
   before being passed to the TLS library.  This didn't seem like a
   significant issue as PB-TNC is architected to layer on PT anyway.

   After considering the different options, it was determined that
   layering the PT protocol on top of the TLS protocol without
   requiring current TLS protocol implementations to change met all the
   requirements and offered the best path toward rapid adoption and
   deployment.  Therefore the following sections describe a PT protocol
   that is carried on top of TLS.

3. PT-TLS Protocol

   This section specifies the PT-TLS protocol, a Posture Transport (PT)
   protocol carried by the Transport Layer Security (TLS) protocol over
   a TCP/IP network.  As shown in Figure 1, this protocol runs directly
   on top of TLS as an application.  This means PT-TLS is encapsulated
   within the TLS Record Layer protocol using the standard ContentType
   for applications (application_data).

     +---------------------------------------------------------------+
     |             TLV Encapsulation of PB-PA message                |
     +---------------------------------------------------------------+
     |                             TLS                               |
     +---------------------------------------------------------------+
     |                             TCP                               |
     +---------------------------------------------------------------+


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     Figure 1: PT-TLS Layering Model

3.1. Initiating a PT-TLS Session

   The PT-TLS protocol may be initiated by a Posture Transport Client
   or a Posture Transport Server.  This flexibility supports different
   use cases.  For example, a Posture Transport Client that wishes to
   trigger a NEA assessment to determine whether its security posture
   is good can start up a PT-TLS session and request a posture
   assessment.  On the other hand, when an endpoint requests access to
   a protected network or resource, a Posture Transport Server can
   start up a PT-TLS session and perform a posture assessment before
   deciding whether to grant access.

   The party that initiates a PT-TLS session is known as the "PT-TLS
   Initiator".  The other party in the session (which receives the
   request to open a PT-TLS session) is known as the "PT-TLS session
   responder".

3.1.1. Issues with Server Initiated PT-TLS Sessions

   In order for a NEA Server to establish a PT-TLS session, the NEA
   Client needs to be listening for a connection request on a TCP port
   known by the NEA Server.  In many deployments, the security policies
   (e.g. firewall software) of an endpoint are designed to minimize the
   number of open inbound TCP/UDP ports that are available to the
   network to reduce the potential attack footprint.  This is one issue
   that makes it difficult for a NEA Server to initiate a PT-TLS
   session.

   Another issue with this scenario involves X.509 certificates. When
   the NEA Server creates a TLS session to the NEA Client, the NEA
   Client is effectively acting as the TLS server during the TLS
   protocol exchange.  This means the NEA Client would typically need
   to possess an X.509 certificate to protect the initial portion of
   the TLS handshake.  In situations where the NEA Server initiates the
   creation of the TLS session, both the NEA Client and NEA Server MUST
   possess X.509 certificates to fully authenticate the session.  For
   many deployments, provisioning X.509 certificates to all NEA Clients
   has scalability and cost issues; therefore, it is recommended that
   the NEA Client not listen for connection requests from the NEA
   Server but instead establish and maintain a TLS session to the NEA
   Server proactively, so either party can initiate an assessment using
   the preexisting TLS session as required.

   In most cases the traditional methods of server certificate ID
   validation will not apply when the NEA Server initiates the
   connection.  In this case, the NEA Client and Server need to follow


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   the certificate path validation rules in RFC 5280 [RFC5280].   In
   addition, each side needs to be able to authorize its peer based
   upon matching Subject and SubjectAltName fields for certificates
   issued by a particular trust root.

   Therefore, NEA Clients SHOULD be capable of establishing and holding
   open a TLS session with the NEA Server immediately after obtaining
   network access.  A NEA Client MAY listen for connection requests
   from the NEA Server and establish a new PT-TLS session when one does
   not already exist.  Because of the potential added complexity, NEA
   Client's support for accepting inbound PT-TLS connections is
   optional to implement.  Having an existing PT-TLS session allows
   either party to initiate an assessment without requiring the NEA
   Client to be listening for new connection requests.  In order to
   keep the TLS session alive, the NEA Client and NEA Server SHOULD be
   capable of supporting the TLS heartbeat protocol [RFC6520].

3.1.2. Establish or Re-Use Existing PT-TLS Session

   A single PT-TLS session can support multiple NEA assessments, which
   can be started by either party (the PT-TLS Initiator or the PT-TLS
   Responder).  The party that starts a NEA assessment is known as the
   "assessment initiator" and the other party is known as the
   "assessment responder".

   If the assessment initiator already has a PT-TLS session to the
   assessment responder, the initiator can re-use this session;
   otherwise, a new PT-TLS session needs to be established.

3.2. TCP Port Usage

   In order for a PT-TLS Initiator to establish a TCP connection to a
   PT-TLS Responder, the initiator needs to know the TCP port number on
   which the responder is listening for assessment requests.  The IANA
   has reserved TCP port number 271 for use by "pt-tls".

3.3. Preventing MITM Attacks with Channel Bindings

   As described in the NEA Asokan Attack Analysis [ASOKAN], a
   sophisticated Man-in-the-Middle (MITM) attack can be mounted against
   NEA systems.  The attacker forwards PA-TNC messages from a healthy
   machine through an unhealthy one so that the unhealthy machine can
   gain network access.  Because there are easier attacks on NEA
   systems, like having the unhealthy machine lie about its
   configuration, this attack is generally only mounted against
   machines with an External Measurement Agent (EMA). The EMA is a
   separate entity, difficult to compromise, which measures and attests
   to the configuration of the endpoint.


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   To protect against NEA Asokan attacks, the Posture Broker Client on
   an EMA-equipped endpoint should pass the tls-unique channel binding
   [RFC5929] for PT-TLS's underlying TLS session to the EMA.  This
   value can then be included in the EMA's attestation and the Posture
   Validator responsible for communicating with the EMA may then
   confirm that the value matches the tls-unique channel binding for
   its end of the connection.  If the values match, the posture sent by
   the EMA and NEA Client is from the same endpoint as the client side
   of the TLS connection (since the endpoint knows the tls-unique
   value), so no man-in-the-middle is forwarding posture. If they
   differ, the Asokan attack has been detected.  The Posture Validator
   MUST fail its verification of the endpoint if the Asokan attack has
   been detected.

3.4. PT-TLS Message Flow

   This section discusses the general flow of messages between the NEA
   Client's Posture Transport Client and the NEA Server's Posture
   Transport Server in order to perform NEA assessments using the PT-
   TLS protocol.

3.4.1. Assessment Triggers

   Initially, the NEA Client or NEA Server will decide that an
   assessment is needed.  What stimulates the decision to perform an
   assessment is outside the scope of this specification, but some
   examples include:

   o  NEA Server becoming aware of suspicious behavior on an endpoint

   o  NEA Server receiving new policies requiring immediate action

   o  NEA Client noticing a change in local security posture

   o  NEA Client wishing to access a protected network or resource

   Because either the NEA Client or NEA Server can trigger the
   establishment of the TLS session and initiate the assessment, this
   document will use the terms "assessment initiator" and the
   "assessment responder".  This nomenclature allows either NEA
   component to fill either of the PT-TLS roles.

3.4.2. PT-TLS Message Exchange Phases

   The PT-TLS message exchange occurs in three distinct phases:



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   o  TLS Setup (including TLS Handshake protocol)

   o  PT-TLS Negotiation

   o  PT-TLS Data Transport

   The TLS Setup phase is responsible for the establishment of the TCP
   connection and the TLS protections for the PT-TLS messages.  The TLS
   Setup phase starts with the establishment of a TCP connection
   between the Posture Transport Client and Posture Transport Server.
   The new connection triggers the TLS server to start the TLS
   Handshake protocol to establish the cryptographic protections for
   the session.  Once the TLS setup phase has completed (after the TLS
   Finished messages), the TLS session MUST NOT be renegotiated.  TLS
   session renegotiation MAY be used before the TLS Setup phase ends
   and the PT-TLS Negotiation phase begins.  This phase also enables
   the establishment of the tls-unique shared secret.  The tls-unique
   shared secret can later be used by PA to protect against some forms
   of man-in-the-middle attack.

   The PT-TLS Negotiation phase is only performed at the start of the
   first assessment on a TLS session.  During this phase, the NEA
   Client and NEA Server discover each other's PT-TLS capabilities and
   establish a context that will apply to all future PT-TLS messages
   sent over the TLS session.  The PT-TLS Negotiation phase MUST NOT be
   repeated after the session has entered the Data Transport phase.
   NEA assessment messages (PB-TNC batches) MUST NOT be sent by the NEA
   Client or NEA Server prior to the completion of the PT-TLS
   Negotiation phase to ensure that the security protections for the
   session are properly established and applied to the NEA assessment
   messages.

   Finally the Data Transport phase allows the NEA Client and NEA
   Server to exchange PT messages under the protection of the TLS
   session consistent with the capabilities established in earlier
   phases.  The exchanged messages can be a PT-TLS protected NEA
   assessment as described in this specification or other vendor-
   defined PT-TLS exchanged messages.

3.4.2.1. TLS Setup Phase

   After a new TCP connection is established between the Posture
   Transport Client and Posture Transport Server, a standard TLS
   exchange is performed to negotiate a common security context for
   protecting subsequent communications.  As discussed in section
   3.4.1, the TCP connection establishment and/or the TLS handshake
   protocol could be initiated by either the NEA Client or NEA Server.
   The most common situation would be for the assessment initiator to


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   trigger the creation of the TCP connection and TLS handshake, so an
   assessment could begin when no session already exists.  When the NEA
   Server has initiated the TLS Setup, the NEA Server is acting as a
   TLS client and the NEA Client is the TLS server (accepting the
   inbound TLS session request).  The expected normal case is that the
   NEA Client initiates this phase, so that the NEA Server is acting as
   the TLS server and therefore the bootstrapping of the security of
   the TLS session is using the NEA Server's certificate.  Having the
   NEA Client initiate the TLS session avoids the need for the NEA
   Client to also possess a certificate.

   During the TLS Setup phase of PT-TLS, the PT-TLS Initiator contacts
   the listening port of the PT-TLS Responder and performs a TLS
   handshake.  The PT-TLS Responder MUST possess a trustworthy X.509
   certificate used to authenticate to the TLS initiator and used to
   bootstrap the security protections of the TLS session.  The PT-TLS
   Initiator MAY also use an X.509 certificate to authenticate to the
   PT-TLS Responder providing for a bi-directional authentication of
   the PT-TLS session.  The NEA client MUST provide certificate
   validation according to the rules in RFC 5280 when evaluating the
   server certificate.  The NEA client MAY perform certificate
   revocation checking on the NEA server's certificate.  This
   specification allows the NEA client implementation to decide on what
   certificate revocation technique is to be implemented.  Note that
   the NEA client performing certificate validation might require some
   network access (e.g. HTTP) to be allowed during the assessment.  NEA
   client network access might be restricted during assessments in some
   situations.

   In addition, the NEA client MUST follow the recommendations in RFC
   6125 [RFC6125] when validating the NEA server domain name against
   the contents of the server certificate, taking into consideration
   the following restrictions:

   o  Any SRV-IDs and URI-IDs in the certificate are ignored

   o  Use of CN-IDs in certificates is NOT RECOMMENDED

   o  Wildcards MUST NOT appear in the DNS-ID or CN-ID of a certificate
      identifying a PT-TLS server.

   Details for the reverse direction are given in section 3.1.
   Due to deployment issues with issuing and distributing certificates
   to a potentially large number of NEA Clients, this specification
   allows the NEA Client to be authenticated during the PT-TLS
   Negotiation phase using other more cost effective methods.  At the
   conclusion of a successful initial TLS Setup phase, the NEA Client



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   and NEA Server have a protected session to exchange messages.  This
   allows the protocol to transition to the PT-TLS Negotiation phase.

3.4.2.2. PT-TLS Negotiation Phase

   Once a TLS session has been established between Posture Transport
   Client and Posture Transport Server, the PT-TLS Initiator sends a
   Version Request Message indicating its supported PT-TLS protocol
   version range.  Next, the PT-TLS Responder sends a Version Response
   Message which selects a protocol version from within the range
   offered.  The PT-TLS Responder SHOULD select the preferred version
   offered if supported; otherwise, the highest version that the
   responder is able to support from the received Version Request
   Message. If the PT-TLS Responder is unable or unwilling to support
   any of the versions included in the Version Request Message, the
   responder SHOULD send a Version Not Supported error message.

   If no client side authentication occurred during the TLS Setup
   phase, the Posture Transport Server can authenticate the client
   using PT-TLS client authentication messages as described in section
   3.8.  The NEA Server initiates the client authentication and
   indicates when the authentication is complete.

   When the NEA Client receives the SASL [RFC4422] Mechanisms list, the
   NEA Client responds with a SASL Mechanism Selection TLV indicating
   the method of authentication to be used.  Upon selecting an
   appropriate SASL mechanism, the NEA Client and Server exchange SASL
   mechanism specific messages in order to authenticate the NEA Client.
   When the client authentication successfully completes and no
   additional authentications are required (as indicated by the NEA
   Server sending an empty SASL Mechanisms list), the PT-TLS session
   transitions into the Data Transport phase, where it will remain for
   the duration of the session.  Note that the NEA Server could choose
   to not authenticate the client (indicated by only sending an empty
   SASL Mechanisms list) or to continue performing a posture assessment
   even if the authentication did not complete successfully.

3.4.2.3. PT-TLS Data Transport Phase

   Once a PT-TLS session is available to carry NEA assessments, PT-TLS
   allows either side of the connection to send the first PB-TNC batch.
   The PB-TNC standard prescribes whether the Posture Broker Client or
   Posture Broker Server starts the assessment.  The assessment
   initiator first envelopes the PB-TNC batch in a PT-TLS message, then
   assigns a message identifier to the message and finally transmits it
   over the session.  The assessment responder validates the PT-TLS




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   message and delivers the encapsulated PB-TNC batch to its upstream
   component (Posture Broker Client or Server).

   Most PT-TLS messages contain PB-TNC batches that house PA-TNC
   requests for posture information or a response containing the
   requested posture information.  The Posture Transport Client and
   Posture Transport Server may also exchange messages between them,
   such as a PT-TLS Error Message indicating that a problem occurred
   processing a message.   During an assessment, the Posture Transport
   Client and Server merely encapsulate and exchange the PB-TNC batches
   and are unaware of the state of the assessment.

   The PT-TLS protocol allows either party to send a PT-TLS message at
   any time, reflecting the full duplex nature of the underlying TLS
   session.  For example, an assessment initiator may send several PT-
   TLS messages prior to receiving any responses from the assessment
   responder.  All implementations of PT-TLS MUST support full duplex
   PT-TLS message exchange.  However, some higher layer NEA protocols
   (e.g. PB-TNC) may not be able to fully make use of the full-duplex
   message exchange.

3.4.3. TLS Requirements

   In order to ensure that strong security is always available for
   deployers and to improve interoperability, this section discusses
   some requirements on the underlying TLS transport used by PT-TLS.
   Whenever TLS is used by this specification, the appropriate version
   (or versions) of TLS will vary over time, based on the widespread
   deployment and known security vulnerabilities.  At the time of this
   writing, TLS version 1.2 [RFC5246] is the most recent version, but
   has a very limited deployment base and might not be readily
   available for implementation.  TLS version 1.0 [RFC2246] and version
   1.1 [RFC4346] are the most widely deployed versions, and will
   provide the broadest interoperability.  Implementations of PT-TLS
   SHOULD support use of TLS 1.2.

   For each TLS version supported, implementations of the PT-TLS MUST
   at least support the TLS_RSA_WITH_AES_128_CBC_SHA cipher suite.
   This cipher suite requires the server to provide a certificate that
   can be used during the key exchange.  Implementations SHOULD NOT
   include support for cipher suites that do not minimally offer PT-TLS
   Responder (typically Posture Transport Server) authentication, such
   as the anonymous Diffie-Hellman cipher suites (e.g.
   TLS_DH_anon_WITH_AES_128_CBC_SHA).  Implementations MUST support RFC
   5746 [RFC5746].  Implementations MAY allow renegotiation to provide
   confidentiality for the client certificate.  If renegotiation is
   allowed implementations need to select the appropriate handshake
   messages as described in RFC 5929 for the tls-unique value.


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3.5. PT-TLS Message Format

   This section describes the format and semantics of the PT-TLS
   message.  Every message sent over a PT-TLS session MUST start with
   the PT-TLS header described in this section.

   The following is the PT-TLS header:
                        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   |           Message Type Vendor ID              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Message Type                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Message Length                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Message Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Message Value (e.g. PB-TNC Batch) . . .        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Reserved

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Message Type Vendor ID

      This field indicates the owner of the name space associated with
      the Message Type.  This is accomplished by specifying the 24 bit
      SMI Private Enterprise Number [PEN] (Vendor ID) of the party who
      owns the Message Type name space.  Consistent with PA-TNC and PB-
      TNC, we depend on the PEN fitting in 24 bits, so if IANA were to
      register a wider PEN than that PEN could not be used with NEA.
      IETF namespace PT-TLS Message Types MUST use zero (0) in this
      field.  For more information about the intended use of NEA
      namespace identifiers, see PA-TNC (RFC 5792) sections 2.1 and
      2.2.

      The PT-TLS Message Type Vendor ID 0xffffff is reserved.  Posture
      Transport Clients and Servers MUST NOT send PT-TLS messages in
      which the PT-TLS Message Type Vendor ID has this reserved value
      (0xffffff).  If a Posture Transport Client or Posture Transport
      Server receives a message containing this reserved value
      (0xffffff) in the PT-TLS Message Type Vendor ID, the recipient



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      SHOULD respond with an Invalid Parameter error code in a PT-TLS
      Error message.

   Message Type

      This field defines the type of the PT-TLS message within the
      scope of the specified Message Type Vendor ID that is included in
      the Message Value field.  The specific IETF defined values
      allowable in this field when the Message Type Vendor ID is the
      IETF SMI Private Enterprise Number value (0) are defined in
      section 3.6.  Recipients of a message containing a Message Type
      Vendor ID and Message Type that is unrecognized SHOULD respond
      with a Type Not Supported error code in a PT-TLS Error message.

      Posture Transport Clients and Posture Transport Servers MUST NOT
      require support for particular vendor-defined PT-TLS Message
      Types in order to interoperate with other PT-TLS compliant
      implementations (although implementations MAY permit
      administrators to configure them to require support for specific
      vendor-defined PT-TLS message types).

      If the PT-TLS Message Type Vendor ID field has the value zero
      (0), then the PT-TLS Message Type field contains an IETF
      namespace PT-TLS Message Type, as listed in the IANA registry.
      IANA maintains a registry of PT-TLS Message Types.  Entries in
      this registry are added following the IANA Specification Required
      policy, following the guidelines in section 6.1.  Section 3.6. of
      this specification defines the initial set of IETF defined PT-TLS
      Message Types.

      The PT-TLS Message Type 0xffffffff is reserved.  Posture
      Transport Clients and Posture Transport Servers MUST NOT send PT-
      TLS messages in which the PT-TLS Message Type has this reserved
      value (0xffffffff).  If a Posture Transport Client or Posture
      Transport Server receives a message in which the PT-TLS Message
      Type has this reserved value (0xffffffff), it SHOULD respond with
      an Invalid Parameter error code in a PT-TLS Error message.

   Message Length

      This field contains the length in octets of the entire PT-TLS
      message (including the entire header).  Therefore, this value
      MUST always be at least 16.  Any Posture Transport Client or
      Posture Transport Server that receives a message with a PT-TLS
      Message Length field whose value is less than 16 SHOULD respond
      with an Invalid Parameter PT-TLS error code.  Similarly, if a
      Posture Transport Client or Posture Transport Server receives a


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      PT-TLS message for a Message Type that has a known Message Length
      and the Message Length indicates a different value (greater or
      less than the expected value), the recipient SHOULD respond with
      an Invalid Parameter PT-TLS error code.

   Message Identifier

      This field contains a value that uniquely identifies the PT-TLS
      message on a per message sender (Posture Transport Client or
      Server) basis.  This value is copied into the body of the PT-TLS
      Error Message so the recipient can determine which message caused
      the error.

      The Message Identifier MUST be a monotonically increasing counter
      starting at zero indicating the number of the messages the sender
      has transmitted over the TLS session.  It is possible that a busy
      or long lived session might exceed 2^32-1 messages sent, so the
      message sender MUST roll over to zero upon reaching the 2^32nd
      message, thus restarting the increasing counter.  During a
      rollover, it is feasible that the message recipient could be
      confused if it keeps track of every previously received Message
      Identifier, so recipients MUST be able to handle roll over
      situations without generating errors.

   Message Value

      The contents of this field vary depending on the particular
      Message Type Vendor ID and Message Type given in the PT-TLS
      header for this PT-TLS message.  This field most frequently
      contains a PB-TNC batch. The contents of this field for each of
      the initial IETF namespace PT-TLS Message Types are defined in
      this specification.

3.6. IETF Namespace PT-TLS Message Types

   This section defines the NEA standard PT-TLS Message Types used to
   carry PT-TLS messages and PB-TNC batches between the Posture
   Transport Client and Posture Transport Server.

   The following table summarizes the initial set of IETF defined
   message type values, which are used with the PT-TLS Message Type
   Vendor ID field set to the IETF SMI PEN (0).  Note that the IANA
   administers PEN value of 0 on behalf of the IETF.  These
   descriptions only apply to the IETF name space.

   Value (Name)                                Definition
   ------------                                ----------


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     0 (Experimental)           Reserved for experimental use.  This
                                type will not offer interoperability
                                but allows for experimentation.  This
                                message type MUST only be sent when
                                the NEA Client and NEA Server are in
                                the Data Transport phase and only on a
                                restricted, experimental network.
                                Compliant implementations MUST send an
                                Invalid Message error code in a PT-TLS
                                Error message if an Experimental
                                message is received.

     1 (Version Request)        Version negotiation request including
                                the range of versions supported by the
                                sender.  This message type MUST only
                                be sent by the TLS session initiator
                                as the first PT-TLS message in the PT-
                                TLS Negotiation phase.  Recipients
                                MUST send an Invalid Message error
                                code in a PT-TLS Error message if a
                                Version Request is received at another
                                time.

     2 (Version Response)       PT-TLS protocol version selected by
                                the responder.  This message type MUST
                                only be sent by the TLS session
                                responder as the second message in the
                                PT-TLS Negotiation phase. Recipients
                                MUST send an Invalid Message error
                                code in a PT-TLS Error message if a
                                Version Response is received at
                                another time.

     3 (SASL Mechanisms)        Sent by the NEA Server to indicate
                                what SASL mechanisms it is willing to
                                use for authentication on this
                                session. This message type MUST only
                                be sent by the NEA Server in the PT-
                                TLS Negotiation phase.  The NEA Client
                                MUST send an Invalid Message error
                                code in a PT-TLS Error message if a
                                SASL Mechanisms message is received at
                                another time.

     4 (SASL Mechanism Selection) Sent by the NEA Client to select a
                                SASL mechanism from the list offered


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                                by the NEA Server.  This message type
                                MUST only be sent by the NEA Client in
                                the PT-TLS Negotiation phase.  The NEA
                                Server MUST send an Invalid Message
                                error code in a PT-TLS Error message
                                if a SASL Mechanism Selection is
                                received after the PT-TLS Negotiation
                                phase.  Once a SASL mechanism has been
                                selected, it may not change until the
                                mechanism completes either
                                successfully or as a failure.

     5 (SASL Authentication Data) Opaque octets exchanged between the
                                NEA Client and NEA Server's SASL
                                mechanisms to perform the client
                                authentication.  This message type
                                MUST only be sent during the PT-TLS
                                Negotiation phase.  Recipients MUST
                                send an Invalid Message error code in
                                a PT-TLS Error message if a SASL
                                Authentication Data message is
                                received after the PT-TLS Negotiation
                                phase.

     6 (SASL Result)            Indicates the result code of the SASL
                                mechanism authentication as described
                                in section 3.8.10.   This message type
                                MUST only be sent by the NEA Server
                                when the NEA Client and NEA Server are
                                in the PT-TLS Negotiation phase.  The
                                NEA Client MUST send an Invalid
                                Message error code in a PT-TLS Error
                                message if a SASL Result is received
                                after the PT-TLS Negotiation phase.

     7 (PB-TNC Batch)           Contains a PB-TNC batch.  For more
                                information on PB-TNC batches see RFC
                                5793 (PB-TNC) section 4.  This message
                                type MUST only be sent when the NEA
                                Client and NEA Server are in the PT-
                                TLS Data Transport phase.  Recipients
                                SHOULD send an Invalid Message error
                                code in a PT-TLS Error message if a
                                PB-TNC Batch is received outside of
                                the Data Transport phase.




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     8 (PT-TLS Error)           PT-TLS Error message as described in
                                section 3.9.  This message type may be
                                used during any PT-TLS phase.

     9+ (Reserved)              These values are reserved for future
                                allocation following guidelines
                                defined in the IANA Considerations
                                section 6.1.  Recipients of
                                unsupported messages in the IETF name
                                space using a message type of 9 or
                                higher MUST respond with a Type Not
                                Supported PT-TLS error code in a PT-
                                TLS Error message.

3.7. PT-TLS Version Negotiation

   This section describes the message format and semantics for the PT-
   TLS protocol version negotiation.  This exchange is used by the PT-
   TLS Initiator to trigger a version negotiation at the start of an
   assessment.  The PT-TLS Initiator MUST send a Version Request
   message as its first PT-TLS message and MUST NOT send any other PT-
   TLS messages on this connection until it receives a Version Response
   message or an Error message.  The PT-TLS Responder MUST complete the
   version negotiation (or cause an error) prior to sending or
   accepting reception of any additional messages.  After the
   successful completion of the version negotiation, both the Posture
   Transport Client and Posture Transport Server MUST only send
   messages compliant with the negotiated protocol version.  Subsequent
   assessments on the same session MUST use the negotiated version
   number and therefore MUST NOT send additional version negotiation
   messages.

3.7.1. Version Request Message

   This message is sent by a PT-TLS Initiator as the first PT-TLS
   message in a PT-TLS session.  This message discloses the sender's
   supported versions of the PT-TLS protocol.  To ensure compatibility,
   this message MUST always be sent using version 1 of the PT-TLS
   protocol.  Recipients of this message MUST respond with a Version
   Response, or a PT-TLS Error message (Version Not Supported or
   Invalid Message).  The following diagram shows the format of the
   Version Request Message:






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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   |    Min Vers   |    Max Vers   |   Pref Vers   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Min Vers

      This field contains the minimum version of the PT-TLS
      protocol supported by the sender.  This field MUST be set to
      1 indicating support for the first version of PT-TLS.
      However, future versions of this specification will probably
      remove this requirement so PT-TLS Responders MUST be
      prepared to receive other values.

   Max Vers

      This field contains the maximum version of the PT-TLS
      protocol supported by the sender.  This field MUST be set to
      1 indicating support for the first version of PT-TLS.
      However, future versions of this specification will probably
      remove this requirement so PT-TLS Responders MUST be
      prepared to receive other values.

   Pref Vers

      This field contains the sender's preferred version of the
      PT-TLS protocol.  This is a hint to the recipient that the
      sender would like this version selected if supported.  The
      value of this field MUST fall within the range of Min Vers
      to Max Vers.  This field MUST be set to 1 indicating support
      for the first version of PT-TLS.  However, future versions
      of this specification will probably remove this requirement
      so PT-TLS Responders MUST be prepared to receive other
      values.

3.7.2. Version Response Message

   This message is sent in response to receiving a Version Request
   Message at the start of a new assessment session.  If a recipient
   receives a Version Request after a successful version negotiation
   has occurred on the session, the recipient MUST send an Invalid


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   Message error code in a PT-TLS Error message and have TLS close the
   session.  This message MUST be sent using the syntax, semantics, and
   requirements of the protocol version specified in this message.

                        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                      |    Version    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Version

      This field contains the version selected by the sender of
      this message.  The version selected MUST be within the Min
      Vers to Max Vers inclusive range sent in the Version Request
      Message.  If a PT-TLS Initiator receives a message with an
      invalid Version selected, the PT-TLS Initiator MUST respond
      with a Version Not Supported PT-TLS error message.

3.8. Client Authentication using SASL

   This section includes a description of the message format and
   semantics necessary to perform client authentication
   (authentication of the NEA Client) over PT-TLS.  Client
   authentication could be necessary if the NEA Server requires
   such an authentication and it was not performed during the TLS
   handshake.  The general model used for performing an
   authentication of the client using PT-TLS messages is to
   integrate the Simple Authentication and Security Layer (SASL)
   [RFC4422] framework.   SASL provides a number of standards-
   based authentication mechanisms capable of authenticating the
   NEA Client using a variety of base technologies.

   Client authentication could occur during the TLS handshake
   using TLS defined authentication techniques.  Because this
   client authentication is optional, the NEA Server's policy
   might require the client to be authenticated by PT-TLS before
   performing the assessment.  Similarly, the NEA Server may
   require a PT-TLS authentication even if the NEA Client was
   authenticated during the TLS handshake (e.g. to allow a user
   authentication after a system level authentication occurred
   during the TLS handshake).  The decision of whether a SASL


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   client authentication is to occur is left to the NEA Server's
   policy.

   As discussed in section 3.1.1, it is possible that the NEA
   Server may initiate the TLS session to the NEA Client, thus
   causing it to fill the role of TLS Client during the TLS
   handshake.  Because the NEA Server is required to possess an
   X.509 certificate for when it is acting as the TLS Server role
   (normal case), PT-TLS requires that the NEA Server MUST use its
   X.509 certificate for TLS client authentication during the TLS
   handshake to authenticate itself even when it is acting as the
   TLS Client.  In this case, the NEA Client and NEA Server will
   authenticate using certificates during the TLS handshake, so
   the PT-TLS SASL client authentication might not be required
   unless NEA Server policy required an additional authentication
   of the NEA Client.  Therefore, the normal usage for the SASL
   messages is when the NEA Client acted as the TLS client and did
   not authenticate during the TLS handshake.

3.8.1. SASL Client Authentication Requirements

   Implementations compliant with the PT-TLS specification MUST
   implement the PT-TLS client authentication messages described
   in this section.  These PT-TLS client authentication messages
   are capable of carrying a variety of SASL authentication
   mechanisms' exchanges.  In order to ensure interoperability,
   all PT-TLS implementations compliant with this specification
   MUST at least support the PLAIN SASL mechanism [RFC4616].
   Similarly, implementations MUST provide the EXTERNAL SASL
   mechanism if both parties are authenticated during the TLS
   establishment.  In order to be able to take advantage of other
   strong, widely deployed authentication technologies such as
   Kerberos and support for channel bindings, implementations MAY
   include support for GS2 (second GSS-API bridge for SASL)
   [RFC5801].  GS2 includes negotiable support for channel binding
   for use with SASL (see section 5 of RFC 5801).

3.8.2. SASL in PT-TLS Overview

   Mechanism negotiation is initiated by the NEA Server sending the
   SASL Mechanisms TLV to the NEA Client to indicate the zero or more
   SASL mechanisms the NEA Server's policy is willing to use with the
   NEA Client.  The NEA Client selects one SASL mechanism from the list
   and sends a SASL Mechanism Selection TLV completing the negotiation.
   Subsequent challenges and responses are carried within the SASL
   Authentication Data TLV carrying the authentication data for the
   selected mechanism.  The authentication outcome is communicated in a


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   SASL Result TLV containing a status code.  If additional
   authentications are required, the NEA Server could trigger the next
   authentication by sending another SASL Mechanisms TLV after sending
   the SASL Result TLV for the current authentication mechanism.

3.8.3. SASL Authentication Flow

   The SASL client authentication starts when the NEA Server
   enters the PT-TLS Negotiation phase and its policy indicates
   that an authentication of the NEA Client is necessary such as
   if it was not performed during the TLS handshake protocol.  The
   NEA Server is responsible for triggering the client
   authentication by sending the SASL Mechanisms TLV to the NEA
   Client listing the set of SASL mechanisms the server is willing
   to use based upon its policy.

   The NEA Client selects a SASL mechanism from the list proposed
   by the NEA Server or sends a PT-TLS Invalid Message error code
   indicating it is unable or unwilling to perform any of the
   mechanisms that were offered.  If the NEA Server receives a
   SASL Mechanism Selection TLV that contains an unacceptable SASL
   mechanism, the NEA Server would respond with a SASL Mechanism
   Error in a PT-TLS Error TLV.

   In situations where the NEA Server does not require a client
   authentication, the NEA Server MUST send a SASL Mechanisms TLV
   with no mechanisms included (only the PT-TLS header) indicating
   the connection should transition to the PT-TLS Data Transport
   phase.  The same mechanism is employed to indicate that a SASL
   authentication already performed in this session is adequate to
   permit transition to the PT-TLS Data Transport phase.  So the
   NEA Server MUST always send a SASL Mechanisms TLV with no
   mechanisms as the last message in the PT-TLS Negotiation phase
   and the NEA Client MUST NOT transition to the PT-TLS Data
   Transport phase until it receives such a message.

   If the NEA Server receives a NEA assessment message before the
   completion of the client authentication, the NEA Server MUST
   send an Authentication Required PT-TLS Error indicating to the
   NEA Client that an authentication exchange is required prior to
   entering the PT-TLS Data Transport phase.

3.8.4. Aborting SASL Authentication

   The NEA Server may abort the authentication exchange by sending the
   SASL Result TLV with a status code of ABORT.  The NEA Client may



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   abort the authentication exchange by sending a PT-TLS Error message
   with an Error Code of SASL Mechanism Error.

3.8.5. Linkages to SASL Framework

3.8.5.1. SASL Service Name

   The service name for PT-TLS is "nea-pt-tls".

3.8.5.2. SASL Authorization Identity

   The PT-TLS protocol does not make use of a SASL authorization
   identity string as described in RFC4422.

3.8.5.3. SASL Security Layer

   The NEA PT-TLS protocol always runs under the protection of TLS.
   SASL security layers are not used and thus MUST be negotiated off
   during SASL authentication.

3.8.5.4. Multiple Authentications

   Only one SASL mechanism authentication may be in progress at any one
   time.  Once a SASL mechanism completes (successfully or
   unsuccessfully) the NEA Server MAY trigger an additional
   authentication by sending a SASL Mechanisms TLV.

3.8.6. SASL Channel Bindings

   SASL channel bindings are used to bind the SASL authentication to
   the outer TLS tunnel to ensure that the authenticating endpoints are
   the same as the TLS endpoints.   For SASL mechanisms that support
   channel bindings the TLS-unique value defined in RFC 5929 is carried
   by the SASL Mechanism.    For most mechanisms this means including
   the tls-unique value with the appropriate prefix defined in RFC 5929
   in the application data portion of the SASL Mechanism channel
   binding data. If the validation of the channel-binding fails then
   the connection MUST be aborted.

3.8.7. SASL Mechanisms

   This TLV is sent by the NEA Server to indicate the list of SASL
   mechanisms that it is willing and able to use to authenticate the
   NEA Client.   Each mechanism name consists of a length followed by a
   name.   The total length of the list is determined by the TLV Length
   field.



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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Rsvd| Mech Len|            Mechanism Name (1-20 bytes)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Rsvd| Mech Len|            Mechanism Name (1-20 bytes)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |

   Rsvd (Reserved)

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Mech Len (Mechanism Name Length)

      The length of the Mechanism-Name field in octets.

   Mechanism Name

      SASL mechanism name adhering to the rules defined in RFC4422
      with no padding.

3.8.8. SASL Mechanism Selection

   This TLV is sent by the NEA Client in order to select a SASL
   mechanism for use on this session.

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Rsvd| Mech Len|            Mechanism Name (1-20 bytes)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Optional Initial Mechanism Response              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Rsvd (Reserved)

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Mech Len (Mechanism Name Length)

      The length of the Mechanism-Name field in octets.

   Mechanism Name


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      SASL mechanism name adhering to the rules defined in
      RFC4422.

   Optional Initial Mechanism Response

      Initial set of authentication information required from the
      NEA Client to kick start the authentication.  This data is
      optional and if not provided would be solicited by the NEA
      Server in the first SASL Authentication Data TLV request.

3.8.9. SASL Authentication Data

   This TLV carries an opaque (to PT-TLS) blob of octets being
   exchanged between the NEA Client and the NEA Server.  This TLV
   facilitates their communications without interpreting any of the
   bytes.  The SASL Authentication Data TLV MUST NOT be sent until a
   SASL mechanism has been established for a session.  The SASL
   Authentication Data TLV associated with the current authentication
   mechanism MUST NOT be sent after a SASL Result is sent with a
   Successful status.  Additional SASL Authentication Data TLVs would
   be sent if the PT-TLS Initiator and Responder desire a subsequent
   SASL authentication to occur but only after another SASL mechanism
   selection exchange occurs.

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                SASL Mechanism Data (Variable Length)          ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   SASL Mechanism Data

      Opaque, variable length set of bytes exchanged between the
      PT-TLS Initiator's SASL mechanism and its peer PT-TLS
      Responder's SASL mechanism.  These bytes MUST NOT be
      interpreted by the PT-TLS layer.

3.8.10. SASL Result

   This TLV is sent by the NEA Server at the conclusion of the SASL
   exchange to indicate the authentication result.  Upon reception of a
   SASL Result TLV indicating an Abort, the NEA Client MUST terminate
   the current authentication conversation.  The recipient may retry
   the authentication in the event of an authentication failure.
   Similarly, the NEA Server may request additional SASL
   authentication(s) be performed after the completion of a SASL


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   mechanism by sending another SASL Mechanisms TLV including any
   mechanisms dictated by its policy.

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Result Code         |    Optional Result Data       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Result Code

      This field contains the result of the SASL authentication
      exchange.

      Value (Name)                                Definition
      ------------                                ----------
       0 (Success)              SASL authentication was successful and
                                identity was confirmed.

       1 (Failure)              SASL authentication failed.  This
                                might be caused by the client
                                providing an invalid user identity
                                and/or credential pair.  Note that
                                this is not a mechanism failure to
                                process the authentication as reported
                                by the Mechanism Failure code.

       2 (Abort)                SASL authentication exchange was
                                aborted by the sender

       3 (Mechanism Failure)    SASL "mechanism failure" during the
                                processing of the client's
                                authentication (e.g. not related to
                                the user's input).  For example, this
                                could occur if the mechanism is unable
                                to allocate memory (e.g. malloc) that
                                is needed to process a received SASL
                                mechanism message.

   Optional Result Data

      This field contains a variable length set of additional data
      for a successful result.  This field MUST be zero length
      unless the NEA Server is returning a Result Code of Success



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      and has more data to return.   For more information on the
      additional data with success in SASL, see RFC 4422.

3.9. Error Message

   This section describes the format and contents of the PT-TLS Error
   Message sent by the NEA Client or NEA Server when it detects a PT-
   TLS level protocol error.  Each error message contains an error code
   indicating the error that occurred, followed by a copy of the
   message that caused the error.

   When a PT-TLS error is received, the recipient MUST NOT respond with
   a PT-TLS error because this could result in an infinite loop of
   error messages being sent.  Instead, the recipient MAY log the
   error, modify its behavior to avoid future errors, ignore the error,
   terminate the assessment, or take other action as appropriate (as
   long as it is consistent with the requirements of this
   specification).

   The Message Value portion of a PT-TLS Error Message contains the
   following information:

                          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   |               Error Code Vendor ID            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Error Code                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Copy of Original Message (Variable Length)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           . . . . . . .                       |

   Reserved

      Reserved for future use.  This field MUST be set to 0 on
      transmission and ignored upon reception.

   Error Code Vendor ID

      This field contains the IANA assigned SMI Private Enterprise
      Number for the vendor whose Error Code name space is being
      used in the message.  For IETF namespace Error Code values
      this field MUST be set to zero (0).  For other vendor-
      defined Error Code name spaces this field MUST be set to the
      SMI Private Enterprise Number of the vendor.

   Error Code


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      This field contains the error code.  This error code exists
      within the scope of Error Code Vendor ID in this message.
      Posture Transport Clients and Posture Transport Servers MUST
      NOT require support for particular vendor-specific PT-TLS
      Error Codes in order to interoperate with other PT-TLS
      compliant implementations (although implementations MAY
      permit administrators to configure them to require support
      for specific PT-TLS error codes).

      When the Error Code Vendor ID is set to the IETF Private
      Enterprise Number, the following table lists the initial
      supported IETF defined numeric error codes:

      Value (Name)                                Definition
      ------------                                ----------
       0 (Reserved)            Reserved value indicates that the PT-
                               TLS Error Message SHOULD be ignored by
                               all recipients.  This MAY be used for
                               debugging purposes to allow a sender
                               to see a copy of the message that was
                               received while a receiver is operating
                               on its contents.

       1 (Malformed Message)   PT-TLS message unrecognized or
                               unsupported.  This error code SHOULD
                               be sent when the basic message content
                               sanity test fails.  The sender of this
                               error code MUST consider it a fatal
                               error and abort the assessment.


       2 (Version Not Supported) This error SHOULD be sent when a PT-
                               TLS Responder receives a PT-TLS
                               Version Request message containing a
                               range of version numbers that doesn't
                               include any version numbers that the
                               recipient is willing and able to
                               support on the session.  All PT-TLS
                               messages carrying the Version Not
                               Supported error code MUST use a
                               Version number of 1.  All parties that
                               receive or send PT-TLS messages MUST
                               be able to properly process an error
                               message that meets this description,
                               even if they cannot process any other
                               aspect of PT-TLS version 1.  The
                               sender and receiver of this error code


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                               MUST consider this a fatal error and
                               close the TLS session after sending or
                               receiving this PT-TLS message.

       3 (Type Not Supported)  PT-TLS message type unknown or not
                               supported.  When a recipient receives
                               a PT-TLS message type that it does not
                               support, it MUST send back this error,
                               ignore the message and proceed.  For
                               example, this could occur if the
                               sender used a Vendor ID for the
                               Message Type that is not supported by
                               the recipient.  This error message
                               does not indicate a fatal error has
                               occurred, so the assessment is allowed
                               to continue.

       4 (Invalid Message)     PT-TLS message received was invalid
                               based on the protocol state.  For
                               example, this error would be sent if a
                               recipient receives a message
                               associated with the PT-TLS Negotiation
                               Phase (such as Version messages) after
                               the protocol has reached the PT-TLS
                               Data Transport Phase. The sender and
                               receiver of this error code MUST
                               consider it a fatal error and close
                               the TLS session after sending or
                               receiving this PT-TLS message.

       5 (SASL Mechanism Error) A fatal error occurred while trying to
                               perform the client authentication.
                               For example, the NEA Client is unable
                               to support any of the offered SASL
                               mechanisms.  The sender and receiver
                               of this error code MUST consider it a
                               fatal error and close the TLS session
                               after sending or receiving this PT-TLS
                               message.

       6 (Invalid Parameter)   The PT-TLS error message sender has
                               received a message with an invalid or
                               unsupported value in the PT-TLS
                               header.  This could occur if the NEA
                               Client receives a PT-TLS message from


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                               the NEA Server with a Message Length
                               of zero (see section 3.5) for
                               details.  The sender and receiver of
                               this error code MUST consider it a
                               fatal error and close the TLS session
                               after sending or receiving this PT-TLS
                               message.

   Copy of Original Message

      This variable length value MUST contain a copy (up to 1024
      bytes) of the original PT-TLS message that caused the error.
      If the original message is longer than 1024 bytes, only the
      initial 1024 bytes will be included in this field.   This
      field is included so the error recipient can determine which
      message sent caused the error.  In particular, the recipient
      can use the Message Identifier field from the Copy of
      Original Message to determine which message caused the
      error.

4. Security Considerations

   This section discusses the major threats potentially faced by each
   binding of the PT protocol and countermeasures provided by the PT-
   TLS protocol.

4.1. Trust Relationships

   In order to understand where security countermeasures are necessary,
   this section starts with a discussion of where the NEA architecture
   envisions some trust relationships between the processing elements
   of the PT-TLS protocol.  Implementations or deployments where these
   trust relationships are not present would need to provide additional
   countermeasures to ensure the proper operation and security of PT-
   TLS (which relies upon these relationships to be trustworthy).  The
   following sub-sections discuss the trust properties associated with
   each portion of the NEA reference model directly involved with the
   processing of the PT-TLS protocol.

4.1.1. Posture Transport Client

   The Posture Transport Client is trusted by the Posture Broker Client
   to:

   o  Not observe, fabricate or alter the contents of the PB-TNC
      batches received from the network


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   o  Not observe, fabricate or alter the PB-TNC batches passed down
      from the Posture Broker Client for transmission on the network

   o  Transmit on the network any PB-TNC batches passed down from the
      Posture Broker Client

   o  Deliver properly security protected messages received from the
      network that are destined for the Posture Broker Client

   o  Provide configured security protections (e.g. authentication,
      integrity and confidentiality) for the Posture Broker Client's
      PB-TNC batches sent on the network

   o  Expose the authenticated identity of the Posture Transport Server
      only to the PB-TNC layer within the NEA Client

   o  Verify the security protections placed upon messages received
      from the network to ensure the messages are authentic and
      protected from attacks on the network

   o  Provide a secure, reliable, in order delivery, full duplex
      transport for the Posture Broker Client's messages

   The Posture Transport Client is trusted by the Posture Transport
   Server to:

   o  Not send malicious traffic intending to harm (e.g. denial of
      service) the Posture Transport Server

   o  Not send malformed messages (e.g. messages lacking PT-TLS header)

   o  Not send invalid or incorrect responses to messages (e.g. errors
      when no error is warranted)

   o  Not ignore or drop messages causing issues for the protocol
      processing (e.g. dropping PT-TLS SASL Authentication Data
      messages)

   o  Verify the security protections placed upon messages received
      from the network to ensure the messages are authentic and
      protected from attacks on the network

4.1.2. Posture Transport Server

   The Posture Transport Server is trusted by the Posture Broker Server
   to:



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   o  Not observe, fabricate or alter the contents of the PB-TNC
      batches received from the network

   o  Not observe, fabricate or alter the PB-TNC batches passed down
      from the Posture Broker Server for transmission on the network

   o  Transmit on the network any PB-TNC batches passed down from the
      Posture Broker Server

   o  Deliver properly security protected messages received from the
      network that are destined for the Posture Broker Server

   o  Provide configured security protections (e.g. authentication,
      integrity and confidentiality) for the Posture Broker Server's
      messages sent on the network

   o  Expose the authenticated identity of the Posture Transport Client
      only to the PB-TNC layer within the NEA Server

   o  Verify the security protections placed upon messages received
      from the network to ensure the messages are authentic and
      protected from attacks on the network

   o  Provide a secure, reliable, in order delivery, full duplex
      transport for the Posture Broker Server's messages

   The Posture Transport Server is trusted by the Posture Transport
   Client to:

   o  Not send malicious traffic intending to harm (e.g. denial of
      service) the Posture Transport Client

   o  Not send malformed messages (e.g. messages lacking PT-TLS header)

   o  Not send invalid or incorrect responses to messages (e.g. errors
      when no error is warranted)

   o  Not ignore or drop messages causing issues for the protocol
      processing (e.g. dropping PT-TLS SASL Result messages)

   o  Verify the security protections placed upon messages received
      from the network to ensure the messages are authentic and
      protected from attacks on the network






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4.2. Security Threats and Countermeasures

   Beyond the trusted relationships assumed in section 4.1 the PT-TLS
   protocol faces a number of potential security attacks that could
   require security countermeasures.

   Generally, the PT-TLS protocol is responsible for offering strong
   security protections for all of the NEA protocols so any threats to
   its ability to protect NEA protocol messages could be very damaging
   to deployments.  Once the message is delivered to the Posture Broker
   Client or Posture Broker Server, the posture brokers are trusted to
   properly and safely process the messages.

4.2.1. Message Theft

   When PT-TLS messages are sent over unprotected network links or
   spanning local software stacks that are not trusted, the contents of
   the messages may be subject to information theft by an intermediary
   party.  This theft could result in information being recorded for
   future use or analysis by the adversary.  Messages observed by
   eavesdroppers could contain information that exposes potential
   weaknesses in the security of the endpoint, or system fingerprinting
   information easing the ability of the attacker to employ attacks
   more likely to be successful against the endpoint.  The eavesdropper
   might also learn information about the endpoint or network policies
   that either singularly or collectively is considered sensitive
   information.  For example, if PT-TLS does not provide
   confidentiality protection, an adversary could observe the PA-TNC
   attributes included in the PT-TLS message and determine that the
   endpoint is lacking patches, or particular sub-networks have more
   lenient policies.

   In order to protect against NEA assessment message theft, the PT-TLS
   protocol provides strong cryptographic authentication, integrity and
   confidentiality protection.  Deployers are strongly encouraged to
   employ best practice of the day TLS ciphers to ensure the
   information remains safe despite advances in technology and
   discovered cipher weaknesses.  The use of bi-directional
   authentication of the assessment transport session ensures that only
   properly authenticated and authorized parties may be involved in an
   assessment dialog.  The PT-TLS protocol also provides strong
   cryptography for all of the PB-TNC and PA-TNC protocol messages
   traveling over the network allowing the message contents to be
   hidden from potential theft by the adversary even if the attacker is
   able to observe the encrypted PT-TLS session.




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4.2.2. Message Fabrication

   Attackers on the network or present within the NEA system could
   introduce fabricated PT-TLS messages intending to trick or create a
   denial of service against aspects of an assessment. For example, an
   adversary could attempt to insert into the message exchange fake PT-
   TLS error codes in order to disrupt communications.

   The PT-TLS protocol provides strong security protections for the
   complete message exchange over the network.  These security
   protections prevent an intermediary from being able to insert fake
   messages into the assessment.  In particular, the TLS's protocol use
   of hashing algorithms provides strong integrity protections that
   allow for detection of any changes in the content of the message
   stream.  Additionally, adversaries are unable to observe the PT-TLS
   protocol exchanges because they are encrypted by the TLS ciphers, so
   would have difficulty in determining where to insert the falsified
   message, since the attacker is unable to determine where the message
   boundaries exist.  Even a successful message insertion did occur;
   the recipient would be able to detect it due to the TLS cipher
   suite's integrity checking failing.

4.2.3. Message Modification

   This attack could allow an active attacker capable of intercepting a
   message to modify a PT-TLS message or transported PA-TNC attribute
   to a desired value to ease the compromise of an endpoint.  Without
   the ability for message recipients to detect whether a received
   message contains the same content as what was originally sent,
   active attackers can stealthily modify the attribute exchange.

   The PT-TLS protocol leverages the TLS protocol to provide strong
   authentication and integrity protections as a countermeasure to this
   theat.  The bi-directional authentication prevents the attacker from
   acting as an active man-in-the-middle to the protocol that could be
   used to modify the message exchange.  The strong integrity
   protections (e.g. hashing) offered by TLS allows PT-TLS message
   recipients to detect message alterations by other types of network
   based adversaries.

4.2.4. Denial of Service

   A variety of types of denial of service attacks are possible against
   the PT-TLS protocol if the message exchanges are left unprotected
   while traveling over the network.   The Posture Transport Client and
   Posture Transport Server are trusted not to participate in the



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   denial of service of the assessment session, leaving the threats to
   come from the network.

   The PT-TLS protocol provides bi-directional authentication
   capabilities in order to prevent a man-in-the-middle on the network
   from becoming an undetected active proxy of PT-TLS messages.
   Because the PT-TLS protocol runs after the TLS handshake and thus
   cipher establishment/use, all of the PT-TLC messages are protected
   from undetected modification that could create a denial of service
   situation.  However it is possible for an adversary to alter the
   message flows causing each message to be rejected by the recipient
   because it fails the integrity checking.

   The PT-TLS protocol operates as an application protocol on top of
   TLS and thus TCP/IP protocols, so is subject to denial of service
   attacks against the TLS, TCP and IP protocols.

4.2.5. NEA Asokan Attacks

   As described in section 3.3 and in the NEA Asokan Attack Analysis
   [ASOKAN], a sophisticated MITM attack can be mounted against NEA
   systems.  The attacker forwards PA-TNC messages from a healthy
   machine through an unhealthy one so that the unhealthy machine can
   gain network access.  Section 3.3 and the NEA Asokan Attack
   Analysis provide a detailed description of this attack and of the
   countermeasures that can be employed against it.

   Because lying endpoint attacks are much easier than Asokan attacks
   and the only known effective countermeasure against lying endpoint
   attacks is the use of an External Measurement Agent (EMA),
   countermeasures against an Asokan attack are not necessary unless an
   EMA is in use.  However, PT-TLS implementers may not know whether an
   EMA will be used with their implementation.  Therefore, PT-TLS
   implementers SHOULD support the Asokan attack countermeasures
   described in section 3.3 by providing the value of the tls-unique
   channel binding to higher layers in the NEA reference model: Posture
   Broker Clients, Posture Broker Servers, Posture Collectors, and
   Posture Validators.

   The Asokan attack can also apply to authentication mechanisms
   carried within TLS.  SASL mechanisms providing channel bindings use
   the tls-unique channel binding data as defined in section 3.3 to
   protect against the attack.






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4.2.6. Trust Anchors

   The TLS protocol bases its trust decision about the signer of the
   certificates received during the TLS authentication using a set of
   trust anchor certificate.  It is essential that these trust anchor
   certificates are integrity protected from unauthorized modification.
   Many common software components (e.g. browsers, operating systems,
   security protocols) include a set of trust anchor certificates that
   are relevant to their operation.  The PT-TLS SHOULD use a PT-TLS
   specific set of trust anchor certificates in order to limit what
   Certificate Authorities are authorized to issue certificates for use
   with NEA.

5. Privacy Considerations

   The role of PT-TLS is to act as a secure transport for PB-TNC and
   other higher layer protocols.  As such, PT-TLS does not directly
   utilize personally identifiable information (PII) except when client
   authentication is enabled.  When client authentication is being
   used, the NEA Client will be asked to use SASL which may disclose a
   local identifier (e.g. username) associated with the endpoint and an
   authenticator (e.g. password) to authenticate that identity.
   Because the identity and authenticator are potentially privacy
   sensitive information, the NEA Client MUST offer a mechanism to
   restrict which NEA Servers will be sent this information.
   Similarly, the NEA Client SHOULD provide an indication to the person
   being identified that a request for their identity has been made in
   case they choose to opt out of the authentication to remain
   anonymous unless no user interface is available.

   PT-TLS provides cryptographic peer authentication, message integrity
   and data confidentiality protections to higher layer NEA protocols
   that may exchange data potentially including PII.  These security
   services can be used to protect any PII involved in an assessment
   from passive and active attackers on the network.  Endpoints sending
   potentially privacy sensitive information SHOULD ensure that the PT-
   TLS security protections (TLS cipher suites) negotiated for an
   assessment of the endpoint are adequate to avoid interception and
   off-line attacks of any long term privacy sensitive information
   unless other network protections are already present.

6. IANA Considerations

   This specification requests the creation of two new IANA
   registries and the assignment of a TCP port number. First, this
   specification requests that IANA permanently reserve the early
   allocated TCP port number 271 for use with the PT-TLS protocol


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   upon publication of this specification as an Internet standard
   RFC.

   This section also defines the contents of two new IANA
   registries: PT-TLS Message Types, and PT-TLS Error Codes.  This
   section explains how these registries work.

   All of the registries defined in this document support IETF
   defined values and vendor-defined values.  To explain this
   phenomenon, we will use the PT-TLS Message Type as an example
   but the other registries work the same way.

   Whenever a PT-TLS Message Type appears on a network, it is
   always accompanied by an SMI Private Enterprise Number (PEN),
   also known as a vendor ID.  If this vendor ID is zero, the
   accompanying PT-TLS Message Type is an IETF namespace value
   listed in the IANA registry for PT-TLS Message Types and its
   meaning is defined in the specification listed for that PT-TLS
   Message Type in that registry.  If the vendor ID is not zero,
   the meaning of the PT-TLS Message Type is defined by the vendor
   identified by the vendor ID (as listed in the IANA registry for
   SMI PENs). The identified vendor is encouraged but not required
   to register with IANA some or all of the PT-TLS Message Types
   used with their vendor ID and publish a specification for each
   of these values.

   This delegation of namespace is analogous to the technique used
   for OIDs.  It can result in interoperability problems if
   vendors require support for particular vendor-specific values.
   However, such behavior is explicitly prohibited by this
   specification, which dictates that "Posture Transport Clients
   and Posture Transport Servers MUST NOT require support for
   particular vendor-specific PT-TLS Error Codes in order to
   interoperate with other PT-TLS compliant implementations
   (although implementations MAY permit administrators to
   configure them to require support for specific PT-TLS error
   codes)."  Similar requirements are included for PT-TLS Message
   Types.

6.1. Designated Expert Guidelines

   For all of the IANA registries defined by this specification,
   new values are added to the registry by following the IANA
   Specification Required policy, using the Designated Expert
   process defined in RFC 5226 [RFC5226].




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   This section provides guidance to designated experts so that
   they may make decisions using a philosophy appropriate for
   these registries.

   The registries defined in this document have plenty of values.
   In most cases, the IETF has approximately 2^32 values available
   for it to define and each vendor has the same number of values
   for its use.  Because there are so many values available,
   designated experts should not be terribly concerned about
   exhausting the set of values.

   Instead, designated experts should focus on the following
   requirements.  All values in these IANA registries MUST be
   documented in a specification that is permanently and publicly
   available. IETF namespace values MUST also be useful, not
   harmful to the Internet, and defined in a manner that is clear
   and likely to ensure interoperability.

   Designated experts should encourage vendors to avoid defining
   similar but incompatible values and instead agree on a single
   IETF reviewed approach and value.  However, it is beneficial to
   document existing practice.

   There are several ways to ensure that a specification is
   permanently and publicly available.  It may be published as an
   RFC.  Alternatively, it may be published in another manner that
   makes it freely available to anyone.  However, in this latter
   case, the vendor MUST supply a copy to the IANA and authorize
   the IANA to archive this copy and make it freely available to
   all if at some point the document becomes no longer freely
   available to all through other channels.

   The following two sections provide guidance to the IANA in
   creating and managing the new IANA registries defined by this
   specification.

6.2. Registry for PT-TLS Message Types

   The name for this registry is "PT-TLS Message Types".  Each
   entry in this registry should include a human-readable name, an
   SMI Private Enterprise Number, a decimal integer value between
   0 and 2^32-1, and a reference to the specification where the
   contents of this message type are defined.  This specification
   must define the meaning of the PT-TLS message type and the
   format and semantics of the PT-TLS Message Value field that
   include the designated Private Enterprise Number in the PT-TLS



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   Message Type Vendor ID field and the designated numeric value
   in the PT-TLS Message Type field.

   The following entries for this registry are defined in this
   document.  Additional entries to this registry are added by
   following the IANA Specification Required policy, consistent
   with the guidelines in section 6.1.

   PEN   Value       Name                 Defining Specification
   ---   -----       ----                 ----------------------
    0      0     Experimental             RFC # Assigned to this I-D
    0      1     Version Request          RFC # Assigned to this I-D
    0      2     Version Response         RFC # Assigned to this I-D
    0      3     SASL Mechanisms          RFC # Assigned to this I-D
    0      4     SASL Mechanism Selection RFC # Assigned to this I-D
    0      5     SASL Authentication Data RFC # Assigned to this I-D
    0      6     SASL Result              RFC # Assigned to this I-D
    0      7     PB-TNC Batch             RFC # Assigned to this I-D
    0      8     PT-TLS Error             RFC # Assigned to this I-D
    0   9-2^32-2 Future Allocation        For future IANA allocation
    0    2^32-1  Permanently Reserved     Not to be assigned by IANA

   The PEN 0 (IETF) PT-TLS Message Type values between 9 and 2^32-2
   inclusive are allocated for future assignment by the IANA.

6.3. Registry for PT-TLS Error Codes

   The name for this registry is "PT-TLS Error Codes".  Each entry
   in this registry should include a human-readable name, an SMI
   Private Enterprise Number, a decimal integer value between 0
   and 2^32-1, and a reference to the specification where this
   error code is defined.  This specification must define the
   meaning of this error code, a PT-TLS Message Type of PT-TLS
   Error, the designated Private Enterprise Number in the PT-TLS
   Error Code Vendor ID field, and the designated numeric value in
   the PT-TLS Error Code field.

   The following entries for this registry are defined in this
   document.  Additional entries to this registry are added
   following the IANA Specification Required policy, consistent
   with the guidelines in section 6.1.








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   PEN  Value       Name                  Defining Specification
   ---  -----       ----                  ----------------------
    0     0     Reserved                 RFC # Assigned to this I-D
    0     1     Malformed Message        RFC # Assigned to this I-D
    0     2     Version Not Supported    RFC # Assigned to this I-D
    0     3     Type Not Supported       RFC # Assigned to this I-D
    0     4     Invalid Message          RFC # Assigned to this I-D
    0     5     SASL Mechanism Error     RFC # Assigned to this I-D
    0     6     Invalid Parameter        RFC # Assigned to this I-D
    0  7-2^32-1 Future Allocation        For future IANA allocation

   The PEN 0 (IETF) PT-TLS Error Codes between 7 and 2^32-1 inclusive
   are allocated for future assignment by the IANA.

7. Acknowledgments

   Thanks to the Trusted Computing Group for contributing the initial
   text upon which this document was based [IFT-TLS].

   The authors of this draft would also like to acknowledge the
   following people who have contributed to or provided substantial
   input on the preparation of this document or predecessors to it:
   Syam Appala, Stuart Bailey, Lauren Giroux, Steve Hanna, Josh
   Howlett, Scott Kelly, Carolin Latze, Sung Lee, Lisa Lorenzin, Alexey
   Melnikov, Ravi Sahita, Subbu Srinivasan, Susan Thomson and Mark
   Townsend.

   This document was prepared using 2-Word-v2.0.template.dot.

8. References

8.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4422] Melnikov A., Zeilenga K., "Simple Authentication and
             Security Layer (SASL)", RFC 4422, June 2006.

   [RFC4616] Zeilenga K., "The PLAIN Simple Authentication and Security
             Layer (SASL) Mechanism", RFC 4616, August 2006.

   [RFC5226] Narten T., Alvestrand H., "Guidelines for Writing an IANA
             Considerations Section in RFCs", RFC 5226, May 2008.

   [RFC5246] Dierks T., Rescorla E., "The Transport Layer Security
             (TLS) Protocol Version 1.2", RFC 5246, August 2008.


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   [RFC5280] Cooper, D., Santesson, S., Farrel, S., Boeyen, S.,
             Housley, R., Polk, W., "Internet X.509 Public Key
             Infrastructure Certificate and Certificate Revocation List
             (CRL) Profile", RFC 5280, May 2008.

   [RFC5746] Rescorla E., Ray M., Oskov N., "Transport Layer Security
             (TLS) Renegotiation Indication Extension", RFC 5746,
             February 2010.

   [RFC5792] Sangster P., Narayan K., "PA-TNC: A Posture Attribute
             Protocol (PA) Compatible with TNC", RFC 5792, March 2010.

   [RFC5793] Sahita, R., Hanna, S., and R. Hurst, "PB-TNC: A Posture
             Broker Protocol (PB) Compatible with TNC", RFC 5793, March
             2010.

   [RFC5929] Altman, J., Williams, N., Zhu L., "Channel Bindings for
             TLS", RFC 5929, July 2010.

   [RFC6125] Saint-Andre, P., Hodges, J., "Representation and
             Verification of Domain-Based Application Service Identity
             within Internet Public Key Infrastructure Using X.509
             (PKIX) Certificates in the Context of Transport Layer
             Security (TLS)", RFC 6125, March 2011.

   [RFC6520] Segglemann, R., Tuexen, M., Williams M., "Transport Layer
             Security (TLS) and Datagram Transport Layer Security
             (DTLS) Heartbeat Extension", RFC 6520, February 2012.

8.2. Informative References

   [ASOKAN]  Salowey, J., Hanna, S., "NEA Asokan Attack Analysis",
             draft-ietf-nea-asokan-00.txt (work in progress), April
             2012.

   [IFT-TLS] Trusted Computing Group, "TNC IF-T: Binding to TLS",
             http://www.trustedcomputinggroup.org/files/resource_files/
             51F0757E-1D09-3519-
             AD63B6FD099658A6/TNC_IFT_TLS_v1_0_r16.pdf, May 2009.

   [PEN]     IANA Private Enterprise Numbers (PEN) registry,
             http://www.iana.org/assignments/enterprise-numbers.

   [PT-EAP]  Cam-Winget, N., S., Sangster, P., "PT-EAP: Posture
             Transport (PT) Protocol For EAP Tunnel Methods", draft-
             ietf-nea-pt-eap-03.txt (work in progress), July 2012.



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   [RFC2246] Dierks, T. and Allen C., "The TLS Protocol Version 1.0",
             RFC 2246, January 1999.

   [RFC4346] Dierks T., Rescorla E., "The Transport Layer Security
             (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC5209] Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
             Tardo, "Network Endpoint Assessment (NEA): Overview and
             Requirements", RFC 5209, June 2008.

   [RFC5801] Josefsson, S., Williams, N., "Using Generic Security
             Service Application Program Interface (GSS-API) Mechanisms
             in Simple Authentication and Security Layer (SASL): The
             GS2 Mechanism Family", RFC 5801, July 2010.

Authors' Addresses

   Paul Sangster
   Symantec Corporation
   6825 Citrine Dr
   Carlsbad, CA 92009

   Email: paul_sangster@symantec.com

   Nancy Cam-Winget
   Cisco Systems
   80 West Tasman Drive
   San Jose, CA  95134
   US

   Email: ncamwing@cisco.com

   Joseph Salowey
   Cisco Systems
   2901 Third Avenue
   Seattle, WA  98121
   US

   Email: jsalowey@cisco.com










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