[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

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

Network Working Group                                        P. Sangster
Internet Draft                                      Symantec Corporation
Intended status: Proposed Standard                         N. Cam-Winget
Expires: September 2011                                       J. Salowey
                                                           Cisco Systems
                                                      September 16, 2011



            PT-TLS: A TCP-based Posture Transport (PT) Protocol
                       draft-ietf-nea-pt-tls-01.txt


Abstract

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

Status of this Memo

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

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

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

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

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

   This Internet-Draft will expire on September 16, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors. All rights reserved.




Sangster et al.         Expires March 16, 2012                 [Page 1]

Internet-Draft                  PT-TLS               September 16, 2011

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................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.......................17
      3.7. PT-TLS Version Negotiation...............................20
         3.7.1. Version Request Message.............................20
         3.7.2. Version Response Message............................21
      3.8. Entity Authentication using SASL.........................22
         3.8.1. SASL Entity Authentication Requirements.............22
         3.8.2. SASL in PT-TLS Overview.............................22
         3.8.3. Initiating the SASL Authentication..................23
         3.8.4. SASL Authentication Flow............................23
         3.8.5. Aborting SASL Authentication........................24
         3.8.6. Linkages to SASL Framework..........................24
            3.8.6.1. SASL Service Name..............................24
            3.8.6.2. SASL Authorization Identity....................24
            3.8.6.3. SASL Security Layer............................24

Sangster et al.         Expires March 16, 2012                 [Page 2]

Internet-Draft                  PT-TLS               September 16, 2011


            3.8.6.4. Multiple Authentications.......................24
         3.8.7. Request SASL Mechanisms.............................24
         3.8.8. SASL Mechanisms.....................................25
         3.8.9. SASL Mechanism Selection............................25
         3.8.10. SASL Authentication Data...........................26
         3.8.11. SASL Result........................................27
      3.9. Error Message............................................28
   4. Security Considerations.......................................31
      4.1. Trust Relationships......................................32
         4.1.1. Posture Transport Client............................32
         4.1.2. Posture Transport Server............................33
      4.2. Security Threats and Countermeasures.....................34
         4.2.1. Message Theft.......................................34
         4.2.2. Message Fabrication.................................35
         4.2.3. Message Modification................................35
         4.2.4. Denial of Service...................................36
         4.2.5. NEA Asokan Attacks..................................36
         4.2.6. Trust Anchors.......................................37
   5. Privacy Considerations........................................37
   6. IANA Considerations...........................................37
      6.1. Designated Expert Guidelines.............................38
      6.2. Registry for PT-TLS Message Types........................39
      6.3. Registry for PT-TLS Error Codes..........................40
   7. Acknowledgments...............................................41
   8. References....................................................41
      8.1. Normative References.....................................41
      8.2. Informative References...................................42
   Appendix A. Evaluation Against NEA Requirements..................43
      A.1. Evaluation Against Requirement C-1.......................43
      A.2. Evaluation Against Requirements C-2......................43
      A.3. Evaluation Against Requirements C-3......................43
      A.4. Evaluation Against Requirements C-4......................43
      A.5. Evaluation Against Requirements C-5......................44
      A.6. Evaluation Against Requirements C-6......................44
      A.7. Evaluation Against Requirements C-7......................45
      A.8. Evaluation Against Requirements C-8......................45
      A.9. Evaluation Against Requirements C-9......................45
      A.10. Evaluation Against Requirements C-10....................46
      A.11. Evaluation Against Requirements C-11....................46
      A.12. Evaluation Against Requirements PT-1....................46
      A.13. Evaluation Against Requirements PT-2....................47
      A.14. Evaluation Against Requirements PT-3....................47
      A.15. Evaluation Against Requirements PT-4....................47
      A.16. Evaluation Against Requirements PT-5....................47
      A.17. Evaluation Against Requirements PT-6 (from PB-TNC
      specification)................................................48



Sangster et al.         Expires March 16, 2012                 [Page 3]

Internet-Draft                  PT-TLS               September 16, 2011


      A.18. Evaluation Against Requirements PT-7 (from PB-TNC
      specification)................................................48
      A.19. Evaluation Against Requirements PT-8 (from PB-TNC
      specification)................................................48
      A.20. Evaluation Against Requirements PT-9 (from PB-TNC
      specification)................................................48

1. Introduction

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


Sangster et al.         Expires March 16, 2012                 [Page 4]

Internet-Draft                  PT-TLS               September 16, 2011


   Multi-byte fields representing numeric values must be sent in network
   (big endian) byte order.

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

1.3. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "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


Sangster et al.         Expires March 16, 2012                 [Page 5]

Internet-Draft                  PT-TLS               September 16, 2011


   assessment during admission followed by reassessment using TCP/IP may
   be appropriate in some environments.
   Some of the benefits to having a TCP/IP based transport during an
   assessment include:

   o  Full Duplex connectivity - 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

Sangster et al.         Expires March 16, 2012                 [Page 6]

Internet-Draft                  PT-TLS               September 16, 2011

   each of the NEA protocols in part because it enables a very space
   efficient representation on the network and is simpler to parse than
   some other encodings to benefit lower powered (or battery
   constrained) devices.

2.4. No Change to Base TLS Protocol

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

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

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

3. PT-TLS Protocol

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



Sangster et al.         Expires March 16, 2012                 [Page 7]

Internet-Draft                  PT-TLS               September 16, 2011


   within the TLS Record Layer protocol using the standard ContentType
   for applications (application_data).

     +---------------------------------------------------------------+
     |             TLV Encapsulation of PB-PA message                |
     +---------------------------------------------------------------+
     |                             TLS                               |
     +---------------------------------------------------------------+
     |                             TCP                               |
     +---------------------------------------------------------------+
     Figure 1: PT-TLS Layering Model

3.1. Initiating a PT-TLS Session

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

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

3.1.1. Issues with Server Initiated PT-TLS Sessions

   In order for a NEA Server to establish a PT-TLS session, the NEA
   Client needs to be listening for a connection request on a TCP port
   known by the NEA Server.  In many deployments, the security policies
   (e.g. firewall software) of an endpoint are designed to minimize the
   number of open inbound TCP/UDP ports that are available to the
   network to reduce the potential attack footprint.  This is one issue
   that makes it difficult for a NEA Server to initiate a PT-TLS
   session.
   Another issue with this scenario involves X.509 certificates. When
   the NEA Server creates a TLS session to the NEA Client, the NEA
   Client is effectively acting as the TLS server during the TLS
   protocol exchange.  This means the NEA Client would typically need to
   possess an X.509 certificate to protect the initial portion of the
   TLS handshake.  In situations where the NEA Server initiates the
   creation of the TLS session, both the NEA Client and NEA Server MUST


Sangster et al.         Expires March 16, 2012                 [Page 8]

Internet-Draft                  PT-TLS               September 16, 2011


   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
   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 Initiator or the PT-TLS
   Responder).  The party that starts a NEA assessment is known as the
   "assessment initiator" and the other party is known as the
   "assessment responder".

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

3.2. TCP Port Usage

   In order for a PT-TLS Initiator to establish a TCP connection to a
   PT-TLS Responder, the initiator needs to know the TCP port number on
   which the responder is listening for assessment requests.  Therefore,
   this specification requests the IANA reserve a 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.

Sangster et al.         Expires March 16, 2012                 [Page 9]

Internet-Draft                  PT-TLS               September 16, 2011


   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 MUST fail its verification
   of the endpoint if an attack has been detected.

3.4. PT-TLS Message Flow

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

3.4.1. Assessment Triggers

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

   o  NEA Server receiving new policies requiring immediate action

   o  NEA Client noticing a change in local security posture

   o  NEA Client wishing to access a protected network or resource

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

3.4.2. PT-TLS Message Exchange Phases

   The PT-TLS message exchange occurs in three distinct phases:
   o  TLS Setup (including TLS Handshake protocol)

   o  PT-TLS Negotiation


Sangster et al.         Expires March 16, 2012                [Page 10]

Internet-Draft                  PT-TLS               September 16, 2011


   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
   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

Sangster et al.         Expires March 16, 2012                [Page 11]

Internet-Draft                  PT-TLS               September 16, 2011


   this phase, so that the NEA Server is acting as the TLS server and
   therefore the bootstrapping of the security of the TLS session is
   using the NEA Server's certificate.  Having the NEA Client initiate
   the TLS session avoids the need for the NEA Client to also possess a
   certificate.

   During the TLS Setup phase of PT-TLS, the PT-TLS Initiator contacts
   the listening port of the PT-TLS Responder and performs a TLS
   handshake.  The PT-TLS Responder MUST possess a trustworthy X.509
   certificate used to authenticate to the TLS initiator and used to
   bootstrap the security protections of the TLS session.  The PT-TLS
   Initiator MAY also use an X.509 certificate to authenticate to the
   PT-TLS Responder providing for a bi-directional authentication of the
   PT-TLS session.

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

   If no client side authentication occurred during the TLS Setup phase,
   the Posture Transport Client can authenticate the client using PT-TLS
   entity authentication messages.  If the Posture Transport Client
   wishes to trigger an authentication of the client, the Posture
   Transport Client SHOULD send a Request SASL Mechanisms and/or SASL
   Mechanism Selection message (see section 3.8.3. for details).  The
   Posture Transport Server MAY also chose to send a SASL Mechanisms
   message without receiving a Request SASL Mechanisms to kick start the
   exchange.


Sangster et al.         Expires March 16, 2012                [Page 12]

Internet-Draft                  PT-TLS               September 16, 2011


   When the Posture Transport Client receives the SASL Mechanisms list,
   the Posture Transport Client responds with a SASL Mechanism Selection
   indicating the method of authentication to be used.  Upon selecting
   an appropriate SASL mechanism, the Posture Transport Client and
   Server exchange SASL mechanism specific messages in order to
   authenticate the client identity on the PT-TLS Initiator.  When the
   client authentication successfully completes and no additional
   authentications are required, the PT-TLS session transitions into the
   Data Transport phase, where it will remain for the duration of the
   session.  Note that the PT-TLS Responder could choose to not
   authenticate the client or to continue performing a posture
   assessment even if the authentication did not complete successfully.

3.4.2.3. PT-TLS Data Transport Phase

   Once a PT-TLS session is available to carry NEA assessments, 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.


Sangster et al.         Expires March 16, 2012                [Page 13]

Internet-Draft                  PT-TLS               September 16, 2011


   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 Responder
   (typically Posture Transport Server) authentication, such as the
   anonymous Diffie-Hellman cipher suites (e.g.
   TLS_DH_anon_WITH_AES_128_CBC_SHA).  Implementations MUST support RFC
   5746 [RFC5746].  Implementations MAY allow renegotiation to provide
   confidentiality for the client certificate.  If renegotiation is
   allowed implementations need to select the appropriate handshake
   messages as described in RFC 5929 for the tls-unique value.

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


Sangster et al.         Expires March 16, 2012                [Page 14]

Internet-Draft                  PT-TLS               September 16, 2011


      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

      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.


Sangster et al.         Expires March 16, 2012                [Page 15]

Internet-Draft                  PT-TLS               September 16, 2011


   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.

   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.






Sangster et al.         Expires March 16, 2012                [Page 16]

Internet-Draft                  PT-TLS               September 16, 2011


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
                                 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 (Request SASL Mechanisms) Sent by the PT-TLS Initiator to
                                 retrieve the set of SASL mechanisms


Sangster et al.         Expires March 16, 2012                [Page 17]

Internet-Draft                  PT-TLS               September 16, 2011


                                 supported by the PT-TLS Responder.
                                 This message type MUST only be sent by
                                 the PT-TLS Initiator in the PT-TLS
                                 Negotiation phase.  Recipients MUST
                                 send an Invalid Message error code in
                                 a PT-TLS Error message if a Request
                                 SASL Mechanisms message is received at
                                 another time.

     4 (SASL Mechanisms)         Sent by the PT-TLS Responder to
                                 indicate what SASL mechanisms it is
                                 willing to use for authentication on
                                 this session.  Recipients MUST send an
                                 Invalid Message error code in a PT-TLS
                                 Error message if a SASL Mechanisms
                                 message is received at another time.

     5 (SASL Mechanism Selection) Sent by the PT-TLS Initiator to select
                                 a SASL mechanism from the list offered
                                 by the PT-TLS Responder or
                                 optimistically (see 3.8.9. for
                                 details).  This message type MUST only
                                 be sent by the PT-TLS Initiator in the
                                 PT-TLS Negotiation phase.  Recipients
                                 MUST send an Invalid Message error
                                 code in a PT-TLS Error message if a
                                 SASL Mechanism Selection is received
                                 after the PT-TLS Negotiation phase.
                                 Once a SASL mechanism has been
                                 selected, it may not change until the
                                 mechanism completes either
                                 successfully or as a failure.

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

     7 (SASL Result)             Indicates the result code of the SASL
                                 mechanism authentication.  A success


Sangster et al.         Expires March 16, 2012                [Page 18]

Internet-Draft                  PT-TLS               September 16, 2011


                                 result indicates that the PT-TLS
                                 Initiator and Responder may transition
                                 to the Data Transport phase, thus
                                 allowing the assessment to start.
                                 Note that the PT-TLS Responder may
                                 choose to allow the transition to Data
                                 Transport phase even if authentication
                                 is unsuccessful before making its
                                 access control decision.  This message
                                 type MUST only be sent by the PT-TLS
                                 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 SASL Result 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.
                                 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.






Sangster et al.         Expires March 16, 2012                [Page 19]

Internet-Draft                  PT-TLS               September 16, 2011


3.7. PT-TLS Version Negotiation

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

3.7.1. Version Request Message

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

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |    Min Vers   |    Max Vers   |   Pref Vers   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved

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

   Min Vers

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


Sangster et al.         Expires March 16, 2012                [Page 20]

Internet-Draft                  PT-TLS               September 16, 2011


   Max Vers

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

   Pref Vers

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

3.7.2. Version Response Message

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


Sangster et al.         Expires March 16, 2012                [Page 21]

Internet-Draft                  PT-TLS               September 16, 2011


      Message.  If a PT-TLS Initiator receives a message with an
      invalid Version selected, the PT-TLS Initiator MUST respond
      with a Version Not Supported PT-TLS error message.

3.8. Entity Authentication using SASL

   This section includes a description of the message format and
   semantics necessary to perform client authentication
   (authentication of the PT-TLS Initiator) over PT-TLS.  The
   general model used for providing an authentication using PT-TLS
   messages over TLS is to integrate the Simple Authentication and
   Security Layer (SASL) [RFC4422] framework.   SASL provides a
   number of standards-based authentication mechanisms capable of
   authenticating the PT-TLS Initiator using a variety of base
   technologies.

   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 entity authentication.  Therefore
   we call this an entity authentication since the entity being
   authenticated could be either the NEA Client or NEA Server.
   Note that normally the NEA Client is being authenticated.

3.8.1. SASL Entity Authentication Requirements

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

3.8.2. SASL in PT-TLS Overview

   Mechanism negotiation is performed using the Request SASL Mechanisms
   and SASL Mechanisms TLVs.  The PT-TLS Initiator sends a Request SASL


Sangster et al.         Expires March 16, 2012                [Page 22]

Internet-Draft                  PT-TLS               September 16, 2011


   Mechanisms TLV to request a preference-ordered list of SASL
   mechanisms that the PT-TLS Responder is willing to use for this
   session.  The PT-TLS Initiator selects one SASL mechanism from the
   list and sends a SASL Mechanism Selection TLV completing the
   negotiation.  Subsequent challenges and responses are carried within
   the SASL Authentication Data TLV carrying the authentication data for
   the selected mechanism.  The authentication outcome is communicated
   in a SASL Result TLV containing a status code.  If additional
   authentications are required, the PT-TLS Responder could trigger the
   next authentication by sending another SASL Mechanisms TLV after
   sending the SASL Result TLV for the current authentication mechanism.

3.8.3. Initiating the SASL Authentication

   Typically the NEA Client would setup the PT-TLS session (see
   section 3.1. ), so the NEA Client would be considered the PT-
   TLS Initiator and thus is the party being authenticated.  The
   PT-TLS Initiator may initiate the entity authentication by
   sending a Request SASL Mechanisms TLV to retrieve the mechanism
   set offered by the PT-TLS Responder (NEA Server) or wait for
   the PT-TLS Responder to send the mechanism set if
   authentication is required by its policy.  The PT-TLS Initiator
   may also proactively send a SASL Mechanism Selection TLV
   proposing a SASL mechanism if it believes is acceptable by the
   PT-TLS Responder without requesting the supported set.  If the
   NEA Server receives a SASL Mechanism Selection TLV that
   contains an unacceptable SASL mechanism, the NEA Server would
   respond with a SASL Mechanism Error in a PT-TLS Error TLV.

   In situations where the PT-TLS Responder does not require an
   entity authentication (either authentication isn't necessary or
   was performed during the TLS Setup phase), the PT-TLS Responder
   would send a SASL Mechanisms TLV with no mechanisms included
   (only the PT-TLS header) when requested.

   In order to avoid race conditions caused by the PT-TLS
   Responder sending an unrequested SASL Mechanisms TLV, the PT-
   TLS Initiator MUST be able to ignore unsolicited SASL
   Mechanisms TLV received immediately after sending a SASL
   Mechanism Selection TLV or the reception of two SASL Mechanisms
   TLVs immediately after sending one SASL Mechanism Request.

3.8.4. SASL Authentication Flow

   If an authentication is required by the PT-TLS Responder and
   not requested by the PT-TLS Initiator, the PT-TLS Responder
   (typically the NEA Server) SHOULD initiate the entity


Sangster et al.         Expires March 16, 2012                [Page 23]

Internet-Draft                  PT-TLS               September 16, 2011


   authentication exchange by sending a SASL Mechanisms TLV.  If
   the PT-TLS Responder receives a NEA assessment message before
   the completion of any required entity authentication, the PT-
   TLS Responder MUST send an Authentication Required PT-TLS Error
   indicating to the PT-TLS Initiator that an authentication
   exchange is required prior to entering the PT-TLS Data
   Transport phase.  The SASL Mechanisms TLV includes a
   preference-ordered list of the SASL mechanisms that the PT-TLS
   Responder is willing to use and allows for the selection of one
   by the PT-TLS Initiator for use with this session.

3.8.5. Aborting SASL Authentication

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

3.8.6. Linkages to SASL Framework

3.8.6.1. SASL Service Name

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

3.8.6.2. SASL Authorization Identity

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

3.8.6.3. SASL Security Layer

   The NEA PT-TLS protocol always runs under the protection of TLS.
   SASL security layers are not used.

3.8.6.4. Multiple Authentications

   Only one SASL mechanism authentication may be in progress at any one
   time.  Once a SASL mechanism completes (successfully or
   unsuccessfully) a new authentication may be initiated.

3.8.7. Request SASL Mechanisms

   This TLV is sent by the PT-TLS Initiator (typically the NEA Client)
   to request that the PT-TLS Responder return the list of SASL
   mechanisms that it is willing and able to use to authenticate.  This
   TLV has no payload (Value field) since the type itself indicates the
   purpose of the TLV to the recipient.  When the PT-TLS Responder
   receives this TLV, it will respond with the SASL Mechanisms TLV.



Sangster et al.         Expires March 16, 2012                [Page 24]

Internet-Draft                  PT-TLS               September 16, 2011


3.8.8. SASL Mechanisms

   This TLV is sent by the PT-TLS Responder (typically NEA Server) to
   indicate the list of SASL mechanisms that it is willing and able to
   use to authenticate the PT-TLS Initiator.   Each mechanism name
   consists of a length followed by a name.   The total length of the
   list is determined by the TLV Length field.  If the PT-TLS Responder
   receives a Request SASL Mechanisms TLV and the PT-TLS Responder does
   not require an authentication to occur, it MUST respond with a SASL
   Mechanisms TLV containing no mechanisms (TLV only includes 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Rsvd| Mech Len|            Mechanism Name (1-20 bytes)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Rsvd| Mech Len|            Mechanism Name (1-20 bytes)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |

   Rsvd (Reserved)

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

   Mech Len (Mechanism Name Length)

      The length of the Mechanism-Name field in octets.

   Mechanism Name

      SASL mechanism name adhering to the rules defined in
      RFC4422.

3.8.9. SASL Mechanism Selection

   This TLV is sent by the PT-TLS Initiator (typically the NEA Client)
   in order to select a SASL mechanism for use on this session.  Because
   the PT-TLS Initiator sends first for the SASL negotiation, it may
   start with Request Mechanisms TLV or just optimistically send a SASL
   Mechanism Selection TLV in hopes it is acceptable to the PT-TLS
   Responder (to avoid a roundtrip).

                          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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Sangster et al.         Expires March 16, 2012                [Page 25]

Internet-Draft                  PT-TLS               September 16, 2011


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


   Rsvd (Reserved)

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

   Mech Len (Mechanism Name Length)

      The length of the Mechanism-Name field in octets.

   Mechanism Name

      SASL mechanism name adhering to the rules defined in
      RFC4422.

   Optional Initial Mechanism Response

      Initial set of authentication information required from the
      PT-TLS Initiator to kick start the authentication.  This
      data is optional and if not provided would be solicited by
      the PT-TLS Responder in the first SASL Authentication Data
      TLV request.

3.8.10. SASL Authentication Data

   This TLV carries an opaque (to PT-TLS) blob of octets being exchanged
   between the PT-TLS Initiator and the PT-TLS Responder.  This TLV
   facilitates their communications without interpreting any of the
   bytes.  The SASL Authentication Data TLV MUST NOT be sent until a
   SASL mechanism has been established for a session.  The SASL
   Authentication Data TLV MUST NOT be sent after a SASL Result is sent
   with a Successful status.

                          1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                SASL Mechanism Data (Variable Length)          ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   SASL Mechanism Data



Sangster et al.         Expires March 16, 2012                [Page 26]

Internet-Draft                  PT-TLS               September 16, 2011


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

3.8.11. SASL Result

   This TLV is sent by the PT-TLS Responder at the conclusion of the
   SASL exchange to indicate the authentication result.  This TLV may
   also be sent by the PT-TLS Initiator to indicate a client side
   failure.  The PT-TLS Initiator MUST NOT send other Result-Code values
   besides Failure.  Upon reception of a SASL Result TLV indicating an
   Abort, the recipient MUST terminate the current authentication
   conversation.  The recipient may retry the authentication in the
   event of an authentication failure.  Similarly, the NEA Server may
   request additional SASL authentication(s) be performed after the
   completion of a SASL mechanism by sending another SASL Mechanisms
   TLV.
                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Result Code         |    Optional Result Data       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      . . . . . . . . . . .                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Result Code

      This field contains the result of the SASL authentication
      exchange.

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

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

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



Sangster et al.         Expires March 16, 2012                [Page 27]

Internet-Draft                  PT-TLS               September 16, 2011


       3 (Mechanism Failure)     SASL mechanism failure during the
                                 processing of the entity's
                                 authentication (not related to the
                                 user's input).

   Optional Result Data

      This field contains a variable length set of additional data
      for a successful result.  This field MUST be zero length
      unless the PT-TLS Responder is returning a Result Code of
      Success and has more data to return.   For more information
      on the additional data, see RFC 4422.

3.9. Error Message

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

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

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

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Reserved   |               Error Code Vendor ID            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Error Code                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Copy of Original Message (Variable Length)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           . . . . . . .                       |

   Reserved

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


Sangster et al.         Expires March 16, 2012                [Page 28]

Internet-Draft                  PT-TLS               September 16, 2011


   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).

      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 Responder receives a PT-TLS
                                 Version Request message containing a
                                 range of version numbers that doesn't


Sangster et al.         Expires March 16, 2012                [Page 29]

Internet-Draft                  PT-TLS               September 16, 2011


                                 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
                                 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 SASL mechanism was unable to
                                 authenticate the claimed identity of
                                 the PT-TLS Initiator.  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


Sangster et al.         Expires March 16, 2012                [Page 30]

Internet-Draft                  PT-TLS               September 16, 2011


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

       6 (Authentication Needed) The PT-TLS Responder has received a
                                 NEA assessment message before the
                                 completion of the entity
                                 authentication.  This could occur if
                                 the NEA Client initiated the PT-TLS
                                 session and then started sending PB
                                 messages before a required (by NEA
                                 Server policy) entity authentication
                                 was performed.  When the PT-TLS
                                 Initiator (typically NEA Client)
                                 receives this error, it should
                                 initiate an entity authentication as
                                 discussed in 3.8.3.


   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.
      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.


Sangster et al.         Expires March 16, 2012                [Page 31]

Internet-Draft                  PT-TLS               September 16, 2011


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
      only to the PB-TNC layer within the NEA Client

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

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

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

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

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


Sangster et al.         Expires March 16, 2012                [Page 32]

Internet-Draft                  PT-TLS               September 16, 2011


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

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

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

4.1.2. Posture Transport Server

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

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

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

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

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

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

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

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

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

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

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


Sangster et al.         Expires March 16, 2012                [Page 33]

Internet-Draft                  PT-TLS               September 16, 2011


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

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

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

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

4.2. Security Threats and Countermeasures

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

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

4.2.1. Message Theft

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

   In order to protect against NEA assessment message theft, the PT-TLS
   protocol provides strong cryptographic authentication, integrity and
   confidentiality protection.  Deployers are strongly encouraged to
   employ best practice of the day TLS ciphers to ensure the information


Sangster et al.         Expires March 16, 2012                [Page 34]

Internet-Draft                  PT-TLS               September 16, 2011


   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.

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


Sangster et al.         Expires March 16, 2012                [Page 35]

Internet-Draft                  PT-TLS               September 16, 2011


   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
   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.



Sangster et al.         Expires March 16, 2012                [Page 36]

Internet-Draft                  PT-TLS               September 16, 2011


4.2.6. Trust Anchors

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

5. Privacy Considerations

   The role of PT-TLS is to act as a secure transport for PB-TNC and
   other higher layer protocols.  As such, PT-TLS does not directly
   utilize personally identifiable information (PII) except when client
   authentication is enabled.  When client authentication is being used,
   the NEA Client will be asked to use SASL which may disclose a local
   identifier (e.g. username) associated with the endpoint and an
   authenticator (e.g. password) to authenticate that identity.  Because
   the identity and authenticator are potentially privacy sensitive
   information, the NEA Client MUST offer a mechanism to restrict which
   NEA Servers will be sent this information.  Similarly, the NEA Client
   should provide an indication to the person being identified that a
   request for their identity has been made in case they choose to opt
   out of the authentication to remain anonymous.

   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 specification requests the creation of two new IANA
   registries and the assignment of a TCP port number. First, this
   specification requests the IANA reserve a registered TCP port
   number for use with the PT-TLS protocol upon publication of
   this specification as an Internet standard RFC.



Sangster et al.         Expires March 16, 2012                [Page 37]

Internet-Draft                  PT-TLS               September 16, 2011


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

   All of the registries defined in this document support IETF
   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.



Sangster et al.         Expires March 16, 2012                [Page 38]

Internet-Draft                  PT-TLS               September 16, 2011


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

   Instead, designated experts should focus on the following
   requirements.  All values in these IANA registries MUST be
   documented in a specification that is permanently and publicly
   available. IETF 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


Sangster et al.         Expires March 16, 2012                [Page 39]

Internet-Draft                  PT-TLS               September 16, 2011


   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.

   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     Request SASL Mechanisms  RFC # Assigned to this I-D
    0      4     SASL Mechanisms          RFC # Assigned to this I-D
    0      5     SASL Mechanism Selection RFC # Assigned to this I-D
    0      6     SASL Authentication Data RFC # Assigned to this I-D
    0      7     SASL Result              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.







Sangster et al.         Expires March 16, 2012                [Page 40]

Internet-Draft                  PT-TLS               September 16, 2011


   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   SASL Mechanism Error         RFC # Assigned to this I-D
    0     7   Authentication Needed        RFC # Assigned to this I-D

7. Acknowledgments

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

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

8. References

8.1. Normative References

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

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

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

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

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

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

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


Sangster et al.         Expires March 16, 2012                [Page 41]

Internet-Draft                  PT-TLS               September 16, 2011


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

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

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

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.

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

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














Sangster et al.         Expires March 16, 2012                [Page 42]

Internet-Draft                  PT-TLS               September 16, 2011


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:



Sangster et al.         Expires March 16, 2012                [Page 43]

Internet-Draft                  PT-TLS               September 16, 2011


   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,
   [IFT-TLS] 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.




Sangster et al.         Expires March 16, 2012                [Page 44]

Internet-Draft                  PT-TLS               September 16, 2011


   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.


Sangster et al.         Expires March 16, 2012                [Page 45]

Internet-Draft                  PT-TLS               September 16, 2011


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.



Sangster et al.         Expires March 16, 2012                [Page 46]

Internet-Draft                  PT-TLS               September 16, 2011


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:



Sangster et al.         Expires March 16, 2012                [Page 47]

Internet-Draft                  PT-TLS               September 16, 2011


   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).



Sangster et al.         Expires March 16, 2012                [Page 48]

Internet-Draft                  PT-TLS               September 16, 2011


   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 than the maximum message size allowable by PB-TNC.











































Sangster et al.         Expires March 16, 2012                [Page 49]

Internet-Draft                  PT-TLS               September 16, 2011


Authors' Addresses

   Paul Sangster
   Symantec Corporation
   6825 Citrine Dr
   Carlsbad, CA 92009

   Email: paul_sangster@symantec.com

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

   Email: ncamwing@cisco.com

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

   Email: jsalowey@cisco.com

























Sangster et al.         Expires March 16, 2012                [Page 50]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/