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Versions: 00 01 02 draft-ietf-nea-pt-tls

Network Working Group                                       P. Sangster
Internet Draft                                     Symantec Corporation
Intended status: Proposed Standard                        March 3, 2011
Expires: September 2011



    PT-TLS: A Posture Transport (PT) Protocol Compatible with TNC Using
                      Transport Layer Security (TLS)
                     draft-sangster-nea-pt-tls-02.txt


Abstract

   This document specifies PT-TLS, a Posture Transport (PT) protocol
   compatible with the Trusted Computing Group's IF-T Binding to TLS 1.0
   protocol.  The document then evaluates PT-TLS against the
   requirements defined in the NEA Overview and Requirements and PB-TNC
   specifications.

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
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on September 3, 2011.

Copyright Notice

   Copyright (c) 2011 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.

Table of Contents

   1. Introduction...................................................4
      1.1. Prerequisites.............................................4
      1.2. Message Diagram Conventions...............................4
      1.3. Conventions used in this document.........................5
   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............................7
   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.......................12
            3.4.2.3. PT-TLS Data Transport Phase....................13
         3.4.3. TLS Requirements....................................13
      3.5. PT-TLS Message Format....................................14
      3.6. IETF Standard PT-TLS Message Types.......................16
      3.7. PT-TLS Version Negotiation...............................19
         3.7.1. Version Request Message.............................19
         3.7.2. Version Response Message............................21
      3.8. Client Authentication Message Exchange...................21
         3.8.1. Client Authentication Request Message...............23
            3.8.1.1. Auth Type Values...............................24
         3.8.2. Client Authentication Selection Message.............25
         3.8.3. Client Authentication Challenge Message.............26
            3.8.3.1. Basic Authentication Challenge.................27
         3.8.4. Client Authentication Response Message..............28
            3.8.4.1. Basic Authentication Information...............29
         3.8.5. Client Authentication Successful Message............30
      3.9. Error Message............................................30


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   4. Security Considerations.......................................34
      4.1. Trust Relationships......................................34
         4.1.1. Posture Transport Client............................34
         4.1.2. Posture Transport Server............................35
      4.2. Security Threats and Countermeasures.....................36
         4.2.1. Message Theft.......................................36
         4.2.2. Message Fabrication.................................37
         4.2.3. Message Modification................................38
         4.2.4. Denial of Service...................................38
         4.2.5. NEA Asokan Attacks..................................38
   5. Privacy Considerations........................................39
   6. IANA Considerations...........................................39
      6.1. Designated Expert Guidelines.............................40
      6.2. Registry for PT-TLS Message Types........................41
      6.3. Registry for PT-TLS Error Codes..........................42
      6.4. Registry for PT-TLS Auth Types...........................43
   7. Acknowledgments...............................................43
   8. References....................................................44
      8.1. Normative References.....................................44
      8.2. Informative References...................................44
   Appendix A. Evaluation Against NEA Requirements..................46
      A.1. Evaluation Against Requirement C-1.......................46
      A.2. Evaluation Against Requirements C-2......................46
      A.3. Evaluation Against Requirements C-3......................46
      A.4. Evaluation Against Requirements C-4......................46
      A.5. Evaluation Against Requirements C-5......................47
      A.6. Evaluation Against Requirements C-6......................47
      A.7. Evaluation Against Requirements C-7......................48
      A.8. Evaluation Against Requirements C-8......................48
      A.9. Evaluation Against Requirements C-9......................48
      A.10. Evaluation Against Requirements C-10....................49
      A.11. Evaluation Against Requirements C-11....................49
      A.12. Evaluation Against Requirements PT-1....................49
      A.13. Evaluation Against Requirements PT-2....................50
      A.14. Evaluation Against Requirements PT-3....................50
      A.15. Evaluation Against Requirements PT-4....................50
      A.16. Evaluation Against Requirements PT-5....................50
      A.17. Evaluation Against Requirements PT-6 (from PB-TNC
      specification)................................................51
      A.18. Evaluation Against Requirements PT-7 (from PB-TNC
      specification)................................................51
      A.19. Evaluation Against Requirements PT-8 (from PB-TNC
      specification)................................................51
      A.20. Evaluation Against Requirements PT-9 (from PB-TNC
      specification)................................................51




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1. Introduction

   This document specifies PT-TLS, a Posture Transport (PT) protocol
   compatible with the Trusted Computing Group's IF-T Binding to TLS 1.0
   protocol [IFT-TLS].  The document then evaluates PT-TLS against the
   applicable requirements defined in the NEA Overview and Requirements
   [RFC5209] and PB-TNC [RFC5793] specifications.

   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.

   The PT protocol in the NEA architecture is responsible for
   transporting PB-TNC 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.  No familiarity with
   TCG specifications is assumed.

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



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   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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 should use
   the PT-EAP (Posture Transport (PT) Protocol for EAP Tunnel Methods)
   [PT-EAP] 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 link layer oriented bindings such as 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:



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   o  Full Duplex connectivity - can send multiple assessment messages
      prior to receiving a response including sending of asynchronous
      messages (e.g. alerts of posture or policy changes)

   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.


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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
   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.  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).






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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
   session 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.

   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.  Having an existing PT-TLS session allows either party


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   to initiate an assessment without requiring the NEA Client to be
   listening for new connection requests.

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 session initiator or the
   PT-TLS session 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 must be established.

3.2. TCP Port Usage

   In order for a PT-TLS session initiator to establish a TCP connection
   to a PT-TLS session responder, the initiator needs to know the TCP
   port number on which the responder is listening for assessment
   requests.  Therefore, this specification requests the IANA reserve a
   well known TCP port number for use with the PT-TLS protocol upon
   publication of this specification as an Internet standard RFC.

3.3. Preventing MITM Attacks with Channel Bindings

   As described 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.
   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.

   To protect against NEA Asokan attacks, the Posture Broker 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, an attack
   has been detected.  The Posture Validator SHOULD fail its
   verification of the endpoint if an attack has been detected.

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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:
      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 normally starts with the establishment of a TCP
   connection between the Posture Transport Client and Posture Transport
   Server.  The new connection triggers the TLS Handshake protocol to
   establish the cryptographic protections for the TLS session.  The TLS
   Setup phase SHOULD NOT be repeated after the PT-TLS Data Transport
   phase has been reached unless a change of TLS cipher suite or keying
   material is required to properly protect the session.  This phase


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   also enables the establishment of the tls-unique shared secret that
   can be used in a later phase to bind the posture sent with this TLS
   connection.

   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 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 session initiator
   contacts the listening port of the TLS session responder and performs
   a TLS handshake.  The PT-TLS session 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 session initiator MAY also use an X.509

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   certificate to authenticate to the PT-TLS session responder providing
   for a bi-directional authentication of the PT-TLS session.
   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
   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 session initiator
   sends a Version Request Message indicating it is supported PT-TLS
   protocol version range.  Next, the PT-TLS session responder sends a
   Version Response Message which selects a protocol version from within
   the range offered.  The PT-TLS session 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 session 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 has occurred during the TLS Setup
   phase, the Posture Transport Server can authenticate the client using
   PT-TLS client authentication messages.  If the Posture Transport
   Server wishes to trigger a client authentication exchange, the
   Posture Transport Server SHOULD send a Client Authentication Request
   message (see section 3.8.1. for details).  The Posture Transport
   Server MAY skip the Client Authentication Request exchange and
   instead start with the client authentication by sending a Client
   Authentication Challenge message if it only supports one type of
   authentication.

   When the Posture Transport Client receives the Client Authentication
   Request, the Posture Transport Client responds with a Client
   Authentication Selection message indicating the method of
   authentication to be used.  Upon selecting an appropriate
   authentication method, the Posture Transport Server requests the
   client's identity and authenticator information using the PT-TLS
   Client Authentication Challenge message.  The Posture Transport
   Client responds with the requested information following the selected
   authentication scheme in a Client Authentication Response message.
   The Posture Transport Client and Server might exchange multiple
   roundtrips of client authentication messages in order to perform the

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   authentication depending on the type of authentication selected.
   When the client authentication successfully completes, the PT-TLS
   session transitions into the Data Transport phase, where it will
   remain for the duration of the session.

3.4.2.3. PT-TLS Data Transport Phase

   Once a PT-TLS session is available to carry NEA assessments, either
   the Posture Transport Client or Server can start an assessment when
   provided a PB-TNC batch for transmission.  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 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 NEA protocols may not be able
   to 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.
   Implementations of PT-TLS MUST support use of TLS 1.1 [RFC4346] and
   SHOULD also include support for TLS 1.2 [RFC5246].  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 session
   responder (typically Posture Transport Server) authentication, such
   as the anonymous Diffie-Hellman cipher suites (e.g.
   TLS_DH_anon_WITH_AES_128_CBC_SHA).


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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 (Vendor ID) of the party who owns
      the Message Type name space.  IETF Standard PT-TLS Message Types
      MUST use zero (0) in this field.

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

   Message Type




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      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 standard 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 and MUST interoperate with other parties despite any
      differences in the set of vendor-defined PT-TLS Message Types
      supported (although they 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 Standard
      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 by Expert Review with Specification Required,
      following the guidelines in section 6.1.  Section 3.6. of this
      specification defines the initial set of IETF Standard 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
      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.


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   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 can be copied into the body of a
      response message to indicate which message was received and
      caused the response.  For example, this field is included in the
      PT-TLS Error Message so the recipient can determine which message
      sent 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 IETF Standard PT-TLS Message Types are defined in this
      specification.

3.6. IETF Standard 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 standard
   message type values, which are used with the PT-TLS Message Type
   Vendor ID field set to the IETF SMI PEN (0).

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


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                                 the Data Transport phase and only on a
                                 restricted, experimental network.
                                 Production code 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 (Client Auth Request)     Request for authentication of client
                                 (PT-TLS session initiator).  This
                                 message includes the PT-TLS session
                                 responder's supported set of
                                 authentication methods.  This message
                                 can be used to start an authentication
                                 of the PT-TLS session initiator.  This
                                 message type MUST only be sent by the
                                 PT-TLS session initiator in the PT-TLS
                                 Negotiation phase.  Recipients MUST
                                 send an Invalid Message error code in
                                 a PT-TLS Error message if a Client
                                 Auth Request message is received at
                                 another time.

     4 (Client Auth Selection)   Authentication method selected by PT-
                                 TLS session initiator.  This message
                                 type MUST only be sent by the PT-TLS
                                 session initiator in response to a


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                                 Client Auth Request message sent in
                                 the PT-TLS Negotiation phase.
                                 Recipients MUST send an Invalid
                                 Message error code in a PT-TLS Error
                                 message if a Client Auth Selection
                                 message is received at another time.

     5 (Client Auth Challenge)   Client authentication challenge from
                                 the PT-TLS session responder (normally
                                 NEA Server).  This message type MUST
                                 only be sent by the PT-TLS session
                                 responder in the PT-TLS Negotiation
                                 phase.  Recipients MUST send an
                                 Invalid Message error code in a PT-TLS
                                 Error message if a Client Auth
                                 Challenge is received after the PT-TLS
                                 Negotiation phase.

     6 (Client Auth Response)    Identity and authenticator information
                                 from the PT-TLS session initiator
                                 (normally NEA Client).  This message
                                 type MUST only be sent by the PT-TLS
                                 session initiator in the PT-TLS
                                 Negotiation phase.  Recipients MUST
                                 send an Invalid Message error code in
                                 a PT-TLS Error message if a Client
                                 Auth Response message is received
                                 after the PT-TLS Negotiation phase.

     7 (Client Auth Success)     Indication that client authentication
                                 was completed successfully so PT-TLS
                                 data messages may now be sent.  This
                                 message type MUST only be sent by the
                                 PT-TLS session responder when the NEA
                                 Client and NEA Server are in the PT-
                                 TLS Negotiation phase.  Recipients
                                 MUST send an Invalid Message error
                                 code in a PT-TLS Error message if a
                                 Client Auth Success is received after
                                 the PT-TLS Negotiation phase.

     8 (PB-TNC Batch)            Contains a PB-TNC batch.  For more
                                 information on PB-TNC batches see
                                 section 4 of the PB-TNC specification.
                                 This message type MUST only be sent
                                 when the NEA Client and NEA Server are
                                 in the PT-TLS Data Transport phase.


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                                 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.

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

     10+ (Reserved)              These values are reserved for future
                                 allocation following guidelines
                                 defined in the IANA Considerations
                                 section 6.1.  Recipients of messages
                                 of type 13 or higher that do not
                                 support the PT-TLS Message Type Vendor
                                 ID and PT-TLS Message Type of a
                                 received PT-TLS message 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 Session Initiator to trigger a version negotiation at the start
   of an assessment.  The PT-TLS session 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 session 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 SHOULD NOT send additional version negotiation
   messages.

3.7.1. Version Request Message

   This message is sent by a PT-TLS Session 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


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   Message).  The following diagram shows the format of the Version
   Request 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   |    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 Session 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 Session 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 Session Responders MUST be prepared to receive
      other values.




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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 SHOULD send an Invalid 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 Session Initiator receives a message
      with an invalid Version selected, the PT-TLS Session
      Initiator MUST respond with a Version Not Supported PT-TLS
      error message.

3.8. Client Authentication Message Exchange

   This section includes a description of the message format and
   contents necessary to perform client authentication
   (authentication of the PT-TLS Session Initiator) over PT-TLS.
   The general model used for providing a client side
   authentication using PT-TLS messages over TLS is to have a
   simple authentication exchange roughly equivalent to basic
   authentication for HTTP [RFC2617] while also allowing for
   extensibility so stronger methods can be added in the future.

   Implementations compliant with the PT-TLS specification MUST
   implement the Basic authentication type described in this
   section.  Future specifications are expected to include
   additional types of authentication.  For example, it is
   expected that a widely used extensible authentication


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   technology such as EAP [RFC3748] will be included in the
   future.

   Because either the NEA Client or NEA Server can initiate the
   TLS session used for the assessment, either could act as the
   TLS server and be authenticated as part of the TLS exchange.
   Therefore, either the NEA Client or NEA Server could also be
   the party not authenticated during the TLS handshake (assuming
   that TLS mutual authentication is not used) and be required to
   authenticate using the PT-TLS client authentication.  Typically
   the NEA Client would setup the PT-TLS session (see section 3.1.
   ), so the NEA Server would be triggering the client
   authentication message exchanges and the NEA Client would be
   the party being authenticated, thus the name "client
   authentication".

   If a client authentication is required, the TLS session
   responder (typically the NEA Server) MUST initiate the client
   authentication exchange by sending a Client Authentication
   Request message or a Client Authentication Challenge message.
   The Client Authentication Request message SHOULD be sent when
   the TLS session responder is willing to authenticate the client
   using multiple alternative authentication methods.  The Client
   Authentication Request message includes a prioritized list of
   the authentication methods that the TLS session responder
   (often the NEA Server) is willing to use and allows for the
   selection of one for use with this session.

   When a TLS session responder is only willing to accept the use
   of a single authentication method, the TLS session responder
   SHOULD optimistically start the authentication exchange by
   sending a Client Authentication Challenge in hopes that the
   other party is willing and able to use the supported type of
   authentication.  If the PT-TLS Session Responder requires an
   authentication of the other party that was not performed during
   the TLS handshake and receives a PT-TLS Data Transport Phase
   message prior to client authentication successfully completing,
   the PT-TLS Session Responder SHOULD ignore the message and
   start the client authentication exchange (if it has not already
   done so). If a TLS Session Initiator receives a Client
   Authentication Challenge or Client Authentication Request as
   the next PT-TLS message after sending its first PT-TLS Data
   Transport Phase message, the initiator MUST assume that the TLS
   session responder requires an authentication prior to entering
   the PT-TLS Data Transport phase.




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   Upon reception of a Client Authentication Request, the
   recipient MUST send a Client Authentication Selection message
   that selects a single authentication method from the list in
   the Client Authentication Request message or send an
   Authentication Error error code in a PT-TLS Error message.
   When the TLS session responder (e.g. NEA Server) receives the
   Client Authentication Selection message, it MUST respond with a
   Client Authentication Challenge message containing the
   challenge information relevant to the selected type of
   authentication.  Some authentication schemes might not require
   an initial challenge from the server so the Client
   Authentication Challenge message might contain minimal
   information and largely serve to start the authentication
   exchange.  After the successful selection of an authentication
   method, the Client Authentication Request and Client
   Authentication Selection messages MUST NOT be used again on the
   session.

   Now that an authentication method has been established, the
   client authentication involves a potentially multi-roundtrip
   message exchange until the PT-TLS Session Responder has
   confirmed the identity of the PT-TLS Session Initiator.  The
   number of roundtrip messages and the contents of each message
   depend on the type of authentication selected.  The client
   authentication messages are described in the following sub-
   sections.

3.8.1. Client Authentication Request Message

   This message is sent when the TLS session responder (e.g. NEA Server)
   has decided that a client authentication is required.  For example,
   this situation could occur following the initial establishment of the
   TLS session performing authentication only of the NEA Server when the
   NEA Server requires an authentication of the NEA Client.
   The following diagram shows the format of the Client Authentication
   Request message.  Note that this message contains a list of Auth Type
   Vendor ID and associated Auth Type fields.  The overall length of the
   PT-TLS message is used by the recipient to determine the number of
   authentication types offered in this message since each entry is 32
   bits in length.








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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Auth Type Vendor ID               |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Auth Type Vendor ID               |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    . . . . . .                |   . . . . .   |

   Auth Type Vendor ID

      This field indicates the owner of the name space associated
      with the following Auth Type field.  Note that this field
      and the following Auth Type field will appear in pairs with
      one pair for every type of authentication being offered by
      the party requesting the authentication.

      This field is the 24 bit SMI Private Enterprise Number
      (Vendor ID) of the party who owns the Auth Type name space
      for the subsequent field.  The IETF standard Auth Type
      values defined in this specification MUST use the IETF SMI
      Private Enterprise Number value (0) in this field.

   Auth Type

      This field indicates a type of authentication that the PT-
      TLS Session Responder is willing to perform in order to
      authenticate the PT-TLS Session Initiator's identity.  The
      ordering of the authentication types in the list SHOULD be
      in the order of preference of the sender with the most
      preferred type first.  Client Authentication Request message
      recipients SHOULD process the list of authentication types
      in the order received and select the first type that is
      acceptable based on local policies.

3.8.1.1. Auth Type Values

   This section defines the IETF standard PT-TLS Auth Types used to
   identify the method of client authentication being used within a PT-
   TLS session.

   Posture Transport Clients and Posture Transport Servers MUST NOT
   require support for particular vendor-specific PT-TLS Auth Types and
   MUST interoperate with other parties despite any differences in the
   set of vendor-specific PT-TLS Auth Types supported (although they MAY
   permit administrators to configure vendor defined authentication
   types to be used).


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   When the PT-TLS Auth Type Vendor ID is set to zero (0), the PT-TLS
   Auth Type is an IETF Standard PT-TLS authentication method. IANA
   maintains a registry of the IETF standard and vendor-specific PT-TLS
   Auth Types.  Entries in this registry are added by Expert Review with
   Specification Required, following the guidelines in section 6.1.

   The following table summarizes the Auth Type values used when the
   Auth Type Vendor ID is set to the IETF SMI PEN (0).

   Value (Name)                             Definition
   ------------                             ----------
     0 (Experimental)            Reserved for experimental use.  This
                                 type will not offer interoperability
                                 but allows for experimentation.  This
                                 value MUST be used only on a
                                 restricted, experimental network.
                                 Production code MUST NOT send an
                                 Experimental Auth Type and MUST send
                                 an Invalid Message error code in a PT-
                                 TLS Error message if an Experimental
                                 Auth Type is received.

     1 (Basic Auth)              Indicates that the Authentication
                                 Information field contains a username
                                 and password as described in section
                                 3.8.4.1.


3.8.2. Client Authentication Selection Message

   This message is sent by the PT-TLS Session Initiator in response to
   reception of a Client Authentication Request message.  This message
   indicates the TLS session initiator's (typically the NEA Client's)
   selection of an authentication method offered in the Client
   Authentication Request message.  The values in this message (Auth
   Type Vendor ID and Auth Type) must match one of the options listed in
   the preceding Client Authentication Request message.  During the
   establishment of the TLS session, the TLS session initiator (e.g. NEA
   Client) MAY authenticate using a TLS defined client authentication
   method such as using client side X.509 certificates.  If the TLS
   client authentication did not occur and is required by the TLS
   session responder, then it SHOULD request the authentication using
   the PT-TLS Client Authentication Request message.

   The following message shows the format of the Client Authentication
   Selection 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Auth Type Vendor ID               |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Auth Type Vendor ID

      This field indicates the owner of the name space associated
      with the following Auth Type field that was selected.  The
      name space owner information is expressed as the 24 bit SMI
      Private Enterprise Number (Vendor ID) of the party who owns
      the Auth Type name space for the subsequent Auth Type field.
      IETF standard values defined in this specification MUST use
      the IETF SMI Private Enterprise Number value of zero (0) in
      this field.

   Auth Type

      This field indicates a type of authentication that was
      selected from the list in the Client Authentication Request
      message received.  The PT-TLS Session Initiator MUST select
      one authentication type (Auth Type Vendor ID and Auth Type)
      from the list sent in the Client Authentication Request
      message or send an Authentication error code in a PT-TLS
      Error message.  The authentication type selection process
      SHOULD process the list in order and select the first type
      that is acceptable based upon its policies.

3.8.3. Client Authentication Challenge Message

   This message is sent by the PT-TLS Session Responder (typically by
   the NEA Server) to initiate the authentication of the PT-TLS Session
   Initiator.  Based upon the type of authentication being performed,
   the contents of the Challenge Information field will vary.  For the
   details of the Challenge Information field for the Basic
   Authentication type see section 3.8.4.1.

   The following message shows the format of the Client Authentication
   Challenge 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Auth Type Vendor ID             |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Challenge Information                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |

   Auth Type Vendor ID

      This field indicates the owner of the name space associated
      with the following Auth Type field that was selected.  The
      name space owner information is expressed as the 24 bit SMI
      Private Enterprise Number (Vendor ID) of the party who owns
      the Auth Type name space for the subsequent field.  IETF
      standard values defined in this specification MUST use the
      IETF SMI Private Enterprise Number value of zero (0) in this
      field.

   Auth Type

      This field indicates the type of client authentication in
      use on the session.  This field also indicates to the
      recipient the contents of the Challenge Information field
      (whose information varies based on authentication type and
      state).

   Challenge Information

      This field contains the authentication challenge in a format
      indicated by the type of authentication.  The detailed
      format and semantics of this field for authentication types
      specified in this document are found in the following
      subsections.

3.8.3.1. Basic Authentication Challenge

   This type of authentication is modeled on HTTP basic authentication.
   This authentication involves the client sending a username and
   password (or passphrase) to the server for authentication.  Note that
   the password will travel over the PT-TLS session without special
   protection but it is afforded the full protections of TLS, so passive
   attacks should be unable to steal these credentials.




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   For the Basic Authentication type of authentication, the Challenge
   Information field is empty.  Basic authentication does not allow for
   the server to send information that alters the authentication
   response.

3.8.4. Client Authentication Response Message

   This message is sent by the PT-TLS Session Initiator to prove its
   identity to the PT-TLS Session Responder.  The format and contents of
   the Authentication Information vary depending on the type of
   authentication being performed and the state of the authentication
   exchange (e.g. when multi-roundtrip authentication protocols are
   used).

   The following message shows the format of the Client Authentication
   Response 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Auth Type Vendor ID              |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Authentication Information                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |

   Auth Type Vendor ID

      This field indicates the owner of the name space associated
      with the following Auth Type field that was selected.  The
      name space owner information is expressed as the 24 bit SMI
      Private Enterprise Number (Vendor ID) of the party who owns
      the Auth Type name space for the subsequent field.  IETF
      standard values defined in this specification MUST use the
      IETF SMI Private Enterprise Number value of zero (0) in this
      field.

   Auth Type

      This field indicates the type of client authentication in
      use on the session.  This field also indicates to the
      recipient the contents of the Challenge Information field
      (whose information varies based on authentication type and
      state).

   Authentication Information



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      This field contains the authentication information in a
      format indicated by the type of authentication.  The
      detailed format and semantics of this field for
      authentication types specified in this document are found in
      the following subsections.

3.8.4.1. Basic Authentication Information

   This type of authentication is modeled on the HTTP basic
   authentication.  This authentication involves the party being
   authenticated (the PT-TLS Session Initiator) sending a username and
   password (or passphrase) as a credential for authentication.
   Typically, the Authentication Information field will include the
   username and password for the NEA Client.  The format and semantics
   are as follows:

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Auth Type Vendor ID              |   Auth Type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Username Length         |            Username           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    . . . . . . . . . . . . .                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Password                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    . . . . . . . . . . . . .                  |

   Auth Type Vendor ID

      This field indicates the owner of the name space associated
      with the following Auth Type field that was selected.  The
      name space owner information is expressed as the 24 bit SMI
      Private Enterprise Number (Vendor ID) of the party who owns
      the Auth Type name space for the subsequent field.  IETF
      standard values defined in this specification MUST use the
      IETF SMI Private Enterprise Number value of zero (0) in this
      field.

   Auth Type

      This field indicates the type of authentication in use on
      the session.  This field also indicates to the recipient the
      contents of the Challenge Information field (whose
      information varies based on authentication type and state).


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   Username Length

      This unsigned integer field indicates the octet length of
      the subsequent Username field.  The Username field is
      variable length and is followed by the Password field that
      is also variable length, so the recipient needs to be able
      to identify the end of the Username and the start of the
      password.

   Username

      This field contains a string containing the identity of the
      party being authenticated.  The Username MUST be encoded as
      a UTF-8 [RFC3629] string. NUL termination MUST NOT be
      employed.

   Password

      This field contains a string containing the authenticator
      associated with the claimed identity in the Username field.
      For the Basic type of authentication, the Password field
      MUST include a UTF-8 encoded string. NUL termination MUST
      NOT be employed.

3.8.5. Client Authentication Successful Message

   This message is sent by the PT-TLS Session Responder to indicate that
   it has successfully completed authentication of the claimed identity
   and the PT-TLS session will now enter the PT-TLS Data Transport
   Phase.  This message does not contain a Message Value field since the
   Message Type carries the only needed semantic (authentication was
   successful).  The Client Authentication Successful message MUST be
   sent by a PT-TLS Session Responder (typically the NEA Server) at the
   completion of a successful authentication to indicate that the PT-TLS
   Session Initiator may now start sending NEA assessment messages.

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,


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   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 standard 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

      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 and MUST interoperate with other parties despite
      any differences in the set of vendor-specific PT-TLS Error
      Codes supported (although they MAY permit administrators to
      configure them to require support for specific PT-TLS error
      codes).




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      When the Error Code Vendor ID is set to the IETF Private
      Enterprise Number, the following table lists the supported
      IETF standard 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 session 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
                                 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


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                                 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 (Failed Authentication) The authentication of the identity of
                                 the client failed.  This could occur
                                 if the sent Username and Password (for
                                 the Basic authentication type) did not
                                 match those expected by the
                                 authenticating party.  This error
                                 message does not indicate a fatal
                                 error has occurred, so the
                                 authentication is allowed to be re-
                                 started.

       5 (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.

       6 (Authentication 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 types of
                                 authentication.  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 contains a copy (up to 1024
      bytes) of the original PT-TLS message that caused the error.


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      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.  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

   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




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   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 Client Authentication Challenge
      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:

   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



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   o  Expose the authenticated identity of the Posture Transport 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 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 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 Client Authentication Successful
      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

4.2. 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


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   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.

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.


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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 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


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   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 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.

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 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.

   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.

6. IANA Considerations

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



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   All of the registries defined in this document support IETF
   standard 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 standard 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 and MUST
   interoperate with other parties despite any differences in the
   set of vendor-specific PT-TLS Error Codes supported (although
   they MAY permit administrators to configure them to require
   support for specific PT-TLS error codes)." Similar requirements
   are included for PT-TLS Message Types and PT-TLS Auth Types.

6.1. Designated Expert Guidelines

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

   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,


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   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 standard 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 standard 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 three 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
   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.  Once this document becomes an RFC, they should
   become the initial entries in the registry for PT-TLS Message
   Types.  Additional entries to this registry are added by Expert
   Review with Specification Required, following the guidelines in
   section 6.1.


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   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     Client Auth Request      RFC # Assigned to this I-D
    0      4     Client Auth Selection    RFC # Assigned to this I-D
    0      5     Client Auth Challenge    RFC # Assigned to this I-D
    0      6     Client Auth Response     RFC # Assigned to this I-D
    0      7     Client Auth Success      RFC # Assigned to this I-D
    0      8     PT-TLS Batch             RFC # Assigned to this I-D
    0      9     Reserved                 RFC # Assigned to this I-D
    0     10     Reserved                 RFC # Assigned to this I-D
    0     11     PT-TLS Error             RFC # Assigned to this I-D
    0     12     Reserved                 RFC # Assigned to this I-D
    0 0xffffffff Reserved                 RFC # Assigned to this I-D

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 and the format and semantics of the
   Error Information field for PT-TLS messages that have a PT-TLS
   Vendor ID of 0, 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.  Once this document becomes an RFC, they should
   become the initial entries in the registry for PT-TLS Error
   Codes.  Additional entries to this registry are added by Expert
   Review with Specification Required, following 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   Failed Authentication        RFC # Assigned to this I-D
    0     5   Invalid Message Error        RFC # Assigned to this I-D
    0     6   Authentication Error         RFC # Assigned to this I-D

6.4. Registry for PT-TLS Auth Types

   The name for this registry is "PT-TLS Auth Types".  Each entry
   in this registry should include a human-readable name, an SMI
   Private Enterprise Number, a decimal integer value between 0
   and 255, and a reference to the specification where this
   authentication type is defined.  This specification must define
   the defined authentication mechanism including the format and
   semantics of the Authentication Information and Challenge
   Information fields for PT-TLS client authentication message
   exchange described in section 3.8.

   The following entries for this registry are defined in this
   document.  Once this document becomes an RFC, they should
   become the initial entries in the registry for PT-TLS Auth
   Types.  Additional entries to this registry are added by Expert
   Review with Specification Required, following the guidelines in
   section 6.1.

   PEN  Value     Name                      Defining Specification
   ---  -----     ----                      ----------------------
    0     0   Experimental                RFC # Assigned to this I-D
    0     1   Basic Auth                  RFC # Assigned to this I-D

7. Acknowledgments

   The author 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: Stuart Bailey,
   Lauren Giroux, Steve Hanna, Josh Howlett, Scott Kelly, Sung Lee, Lisa
   Lorenzin, Ravi Sahita, and Mark Townsend.

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






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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.

   [RFC2617] Franks, J.,  P. Hallam-Baker, J. Hostetler, S. Lawrence, P.
             Leach, A. Luotonen, and L. Stewart, "HTTP Authentication:
             Basic and Digest Access Authentication", RFC 2617, June
             1999.

   [RFC3629] Yergeau F., "UTF-8, a transformation format of ISO 10646",
             RFC 3629, November 2003.

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

   [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.

8.2. Informative References

   [ASOKAN]  Salowey, J., Hanna, S., "NEA Asokan Attack Analysis",
             draft-salowey-nea-asokan-00.txt (work in progress), October
             2010.

   [IFT-TLS] Trusted Computing Group, "TNC IF-T: Binding to TLS",
             http://www.trustedcomputinggroup.org/files/resource_files/5
             1F0757E-1D09-3519-
             AD63B6FD099658A6/TNC_IFT_TLS_v1_0_r16.pdf, May 2009.

   [PT-EAP]  Hanna, S., Sangster, P., "PT-EAP: Posture Transport (PT)
             Protocol For EAP Tunnel Methods", draft-hanna-nea-pt-eap-
             01.txt (work in progress), March 2011.




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   [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
             Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
             3748, June 2004.

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

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





































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Appendix A.                 Evaluation Against NEA Requirements

   This section evaluates the PT-TLS protocol against the PT
   requirements defined in the NEA Overview and Requirements and
   PB-TNC specifications.  Each subsection considers a separate
   requirement and highlights how PT-TLS meets the requirement.

A.1. Evaluation Against Requirement C-1

   Requirement C-1 says:

   C-1   NEA protocols MUST support multiple round trips between
   the NEA Client and NEA Server in a single assessment.

   PT-TLS meets this requirement.  Use of the TLS protocol over
   TCP/IP allows for multiple round trips of PT-TLS messages,
   which can carry multiple round trips of PB-TNC batches.

A.2. Evaluation Against Requirements C-2

   Requirement C-2 says:

   C-2   NEA protocols SHOULD provide a way for both the NEA
   Client and the NEA Server to initiate a posture assessment or
   reassessment as needed.

   PT-TLS meets this requirement.  PT-TLS allows the NEA Client or
   the NEA Server to initiate a posture assessment or
   reassessment.

A.3. Evaluation Against Requirements C-3

   Requirement C-3 says:

   C-3   NEA protocols including security capabilities MUST be
   capable of protecting against active and passive attacks by
   intermediaries and endpoints including prevention from replay
   based attacks.

   PT-TLS meets this requirement.  The use of TLS provides strong
   cryptographic authentication, integrity and confidentiality
   services for the NEA protocols.

A.4. Evaluation Against Requirements C-4

   Requirement C-4 says:



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   C-4   The PA and PB protocols MUST be capable of operating over
   any PT protocol.  For example, the PB protocol must provide a
   transport independent interface allowing the PA protocol to
   operate without change across a variety of network protocol
   environments (e.g. EAP/802.1X, PANA, TLS and IKE/IPsec).

   While this requirement is not applicable to PT, the PT-TLS
   protocol is independent of PA and PB allowing those protocols
   to operate over other PT protocols.

A.5. Evaluation Against Requirements C-5

   Requirement C-5 says:

   C-5   The selection process for NEA protocols MUST evaluate and
   prefer the reuse of existing open standards that meet the
   requirements before defining new ones.  The goal of NEA is not
   to create additional alternative protocols where acceptable
   solutions already exist.

   Based on this requirement, PT-TLS should receive a strong
   preference.  PT-TLS is equivalent with IF-T Binding to TLS 1.0,
   an open TCG specification.  Selecting PT-TLS as the basis for
   the PT protocol will ensure compatibility with IF-T Binding to
   TLS, and with its implementations.

A.6. Evaluation Against Requirements C-6

   Requirement C-6 says:

   C-6   NEA protocols MUST be highly scalable; the protocols MUST
   support many Posture Collectors on a large number of NEA
   Clients to be assessed by numerous Posture Validators residing
   on multiple NEA Servers.

   PT-TLS meets this requirement.  The PT-TLS protocol is
   independent of the quantity or size of the PA-TNC messages and
   the number of Posture Collectors and Posture Validators.  PT-
   TLS provides the Posture Broker Client and Posture Broker
   Server a transport capable of carrying PT-TNC batches up to
   2^32-16 octets in length.  Posture Broker Clients and Posture
   Broker Servers wishing to send a PB-TNC batch longer than 2^32-
   16 octets could opt to split up set of attributes into multiple
   PB-TNC batches and send them sequentially since PT-TLS is full
   duplex.




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   The fields present in the PT-TLS protocol are also very
   scalable, allowing for the definition of a large (2^32) number
   of IETF standard and vendor-defined PT-TLS message types and
   message identifiers.

A.7. Evaluation Against Requirements C-7

   Requirement C-7 says:

   C-7   The protocols MUST support efficient transport of a large
   number of attribute messages between the NEA Client and the NEA
   Server.

   PT-TLS meets this requirement.  PT-TLS will allow for transport
   of a very large number of attributes leveraging the underlying
   TCP/IP network access.  The PT-TLS protocol only adds 16 octets
   of overhead per PT-TLS message, which is negligible since a
   single PT-TLS message might carry very many PA-TNC attributes
   within a single PB-TNC batch.

A.8. Evaluation Against Requirements C-8

   Requirement C-8 says:

   C-8   NEA protocols MUST operate efficiently over low bandwidth
   or high latency links.

   PT-TLS protocols meet this requirement.  TLS will operate well
   over high latency or low bandwidth links leveraging TCP's
   ability to adjust to the underlying network carrier.  The NEA
   protocols encapsulated by the PT-TLS protocol are designed to
   be able to operate over EAP with long RADIUS proxy chains so
   they can adapt to high latency or low bandwidth links. With the
   small amount of overhead added by PT-TLS, TLS, and TCP/IP,
   these protocols should still be efficient over high latency or
   low bandwidth networks.

A.9. Evaluation Against Requirements C-9

   Requirement C-9 says:

   C-9   For any strings intended for display to a user, the
   protocols MUST support adapting these strings to the user's
   language preferences.

   PT-TLS meets this requirement.  The PT-TLS protocol does not
   include messages intended for display to the user.


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A.10. Evaluation Against Requirements C-10

   Requirement C-10 says:

   C-10  NEA protocols MUST support encoding of strings in UTF-8
   format.

   PT-TLS meets this requirement.  All strings in the PT-TLS
   protocol are encoded in UTF-8 format.  This allows the protocol
   to support a wide range of languages efficiently.

A.11. Evaluation Against Requirements C-11

   Requirement C-11 says:

   C-11  Due to the potentially different transport
   characteristics provided by the underlying candidate PT
   protocols, the NEA Client and NEA Server MUST be capable of
   becoming aware of and adapting to the limitations of the
   available PT protocol.  For example, some PT protocol
   characteristics that might impact the operation of PA and PB
   include restrictions on: which end can initiate a NEA
   connection, maximum data size in a message or full assessment,
   upper bound on number of roundtrips, and ordering (duplex) of
   messages exchanged.  The selection process for the PT protocols
   MUST consider the limitations the candidate PT protocol would
   impose upon the PA and PB protocols.

   PT-TLS meets this requirement.  The PT-TLS protocol leverages
   the underlying TLS connection to offer a reliable, full duplex
   session capable of being initiated by the NEA Client or NEA
   Server.  This TLS session allows for transmission of large PB-
   TNC batches with many roundtrips with very low overhead (only
   16 octets of protocol overhead per PT-TLS message).

A.12. Evaluation Against Requirements PT-1

   Requirement PT-1 says:

   PT-1 The PT protocol MUST NOT interpret the contents of PB
   messages being transported, i.e., the data it is carrying must
   be opaque to it.

   PT-TLS meets this requirement.  The PT-TLS protocol
   encapsulates PB-TNC batches without interpreting their
   contents.



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A.13. Evaluation Against Requirements PT-2

   Requirement PT-2 says:

   PT-2 The PT protocol MUST be capable of supporting mutual
   authentication, integrity, confidentiality, and replay
   protection of the PB messages between the Posture Transport
   Client and the Posture Transport Server.

   PT-TLS meets this requirement.  The PT-TLS protocol leverages
   TLS to provide mutual authentication, integrity protection and
   confidentiality as well as replay protection.  For more
   information see the Security Considerations section 4.

A.14. Evaluation Against Requirements PT-3

   Requirement PT-3 says:

   PT-3 The PT protocol MUST provide reliable delivery for the PB
   protocol.  This includes the ability to perform fragmentation
   and reassembly, detect duplicates, and reorder to provide in-
   sequence delivery, as required.

   PT-TLS meets this requirement.  The PT-TLS protocol operates
   over TCP/IP which provides fragmentation/reassembly services
   and can detect/discard duplicate message and re-order messages
   if they arrive out of order over the network.  PT-TLS provides
   a reliable, in-order delivery NEA message transport to the
   Posture Broker Client and Posture Broker Server components.

A.15. Evaluation Against Requirements PT-4

   Requirement PT-4 says:

   PT-4 The PT protocol SHOULD be able to run over existing
   network access protocols such as 802.1X and IKEv2.

   PT-TLS does NOT meet this requirement as it's intended for a
   different usage.  PT-TLS protocol requires the use of a TCP/IP
   connection to the network.  PT-EAP (PT Binding to EAP Tunnel
   Methods) meets this requirement.  PT-TLS is intended to be used
   after the endpoint has been admitted to the network.

A.16. Evaluation Against Requirements PT-5

   Requirement PT-5 says:



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   PT-5 The PT protocol SHOULD be able to run between a NEA Client
   and NEA Server over TCP or UDP (similar to Lightweight
   Directory Access Protocol (LDAP)).

   PT-TLS meets this requirement.  The PT-TLS protocol operates on
   top of an existing TCP/IP connection using TLS for network
   security.

A.17. Evaluation Against Requirements PT-6 (from PB-TNC specification)

   Requirement PT-6 says:

   PT-6 The PT protocol MUST be connection oriented; it MUST
   support confirmed initiation and close down.

   PT-TLS meets this requirement.  The PT-TLS protocol operates on
   top of an existing TCP/IP connection which is connection
   oriented and supports confirmed initiation and tear down of the
   connection.

A.18. Evaluation Against Requirements PT-7 (from PB-TNC specification)

   Requirement PT-7 says:

   PT-7 The PT protocol MUST be able to carry binary data.

   PT-TLS meets this requirement.  The PT-TLS protocol is capable
   of carrying binary data.

A.19. Evaluation Against Requirements PT-8 (from PB-TNC specification)

   Requirement PT-8 says:

   PT-8 The PT protocol MUST provide mechanisms for flow control
   and congestion control.

   PT-TLS meets this requirement.  The PT-TLS protocol operates on
   top of TCP/IP which provides flow and congestion control.

A.20. Evaluation Against Requirements PT-9 (from PB-TNC specification)

   Requirement PT-9 says:

   PT-9 PT protocol specifications MUST describe the capabilities
   that they provide for and limitations that they impose on the
   PB protocol (e.g. half/full duplex, maximum message size).



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   PT-TLS meets this requirement.  This specification discusses
   the level of transport service provided to the Posture Broker
   Client and Posture Broker Server.  Generally, the PT-TLS
   protocol supports the post network admission usages discussed
   in RFC 5209.  The maximum message size for PT-TLS is only 16
   octets less then the maximum message size allowable by PB-TNC.











































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Authors' Addresses

   Paul Sangster
   Symantec Corporation
   6825 Citrine Dr
   Carlsbad, CA 92009

   Email: paul_sangster@symantec.com









































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