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Versions: (draft-hanna-nea-pt-eap) 00 01 02 03 04 05 06 07 08 09 RFC 7171

NEA                                                   N. Cam-Winget, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Informational                             Sangster, Ed.
Expires: September 11, 2012                         Symantec Corporation
                                                          March 10, 2012


     PT-EAP: Posture Transport (PT) Protocol For EAP Tunnel Methods
                        draft-ietf-nea-pt-eap-01

Abstract

   This document specifies PT-EAP, an EAP based Posture Transport (PT)
   protocol designed to be used only inside TLS protected tunnel method.
   As such, the document also describes the intended applicability of
   PT-EAP as well as the evaluation against the requirements defined in
   the NEA Requirements and PB-TNC specifications.

Status of this Memo

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

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

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

   This Internet-Draft will expire on September 11, 2012.

Copyright Notice

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

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



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Prerequisites  . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Message Diagram Conventions  . . . . . . . . . . . . . . .  3
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.4.  Conventions used in this document  . . . . . . . . . . . .  4
     1.5.  Compatibility with other Specifications  . . . . . . . . .  4
   2.  Use of PT-EAP  . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  definition of PT-EAP . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Protocol Overview  . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Version Negotiation  . . . . . . . . . . . . . . . . . . .  6
     3.3.  PT-EAP Message Format  . . . . . . . . . . . . . . . . . .  6
     3.4.  Preventing MITM Attacks with Channel Bindings  . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     4.1.  Trust Relationships  . . . . . . . . . . . . . . . . . . .  9
       4.1.1.  Posture Transport Client . . . . . . . . . . . . . . .  9
       4.1.2.  Posture Transport Server . . . . . . . . . . . . . . . 10
     4.2.  Security Threats and Countermeasures . . . . . . . . . . . 11
       4.2.1.  Message Theft  . . . . . . . . . . . . . . . . . . . . 11
       4.2.2.  Message Fabrication  . . . . . . . . . . . . . . . . . 12
       4.2.3.  Message Modification . . . . . . . . . . . . . . . . . 13
       4.2.4.  Denial of Service  . . . . . . . . . . . . . . . . . . 13
       4.2.5.  NEA Asokan Attacks . . . . . . . . . . . . . . . . . . 13
     4.3.  Requirements for EAP Tunnel Methods  . . . . . . . . . . . 14
     4.4.  Candidate EAP Tunnel Method Protections  . . . . . . . . . 15
     4.5.  Security Claims for PT-EAP as per RFC3748  . . . . . . . . 16
   5.  Privacy Considerations . . . . . . . . . . . . . . . . . . . . 16
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
     6.1.  Registry for PT-EAP Versions . . . . . . . . . . . . . . . 17
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20













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1.  Introduction

   This document specifies PT-EAP, a Posture Transport (PT) protocol
   protected by an outer TLS tunnel or equivalent protection.  The PT
   protocol in the NEA architecture is responsible for transporting PB-
   TNC batches (often containing PA-TNC [RFC5792] attributes) across the
   network between the NEA Client and NEA Server.  The PT protocol must
   be protected by an outer TLS-based tunnel to ensure the exchanged
   messages are protected from a variety of threats from hostile
   intermediaries.

   NEA protocols are intended to be used both 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 types of PT protocols are needed.  One type of PT
   operates after the endpoint has an assigned IP address, layering on
   top of the IP protocol to carry a NEA exchange.  The other type of PT
   operates before the endpoint gains any access to the IP network.
   This specification defines PT-EAP, the PT protocol used to assess
   endpoints before they gain access to the network.

   PT-EAP is an inner EAP [RFC3748] method designed to be used under a
   protected tunnel such as EAP-FAST [RFC4851] or EAP-TTLS [RFC5281].

1.1.  Prerequisites

   This document does not define an architecture or reference model.
   Instead, it defines a protocol that works within the reference model
   described in the NEA Requirements specification [RFC5209].  The
   reader is assumed to be thoroughly familiar with that document.

1.2.  Message Diagram Conventions

   This specification defines the syntax of PT-EAP messages using
   diagrams.  Each diagram depicts the format and size of each field in
   bits.  Implementations MUST send the bits in each diagram as they are
   shown, traversing the diagram from top to bottom and then from left
   to right within each line (which represents a 32-bit quantity).
   Multi-byte fields representing numeric values MUST be sent in network
   (big endian) byte order.

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






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1.3.  Terminology

   This document reuses many terms defined in the NEA Requirements
   document [RFC5209], such as Posture Transport Client and Posture
   Transport Server.  The reader is assumed to have read that document
   and understood it.

   When defining the PT-EAP method, this specification does not use the
   terms "EAP peer" and "EAP authenticator".  Instead, it uses the terms
   "NEA Client" and "NEA Server" since those are considered to be more
   familiar to NEA WG participants.  However, these terms are equivalent
   for the purposes of these specifications.  The part of the NEA Client
   that terminates PT-EAP (generally in the Posture Transport Client) is
   the EAP peer for PT-EAP.  The part of the NEA Server that terminates
   PT-EAP (generally in the Posture Transport Server) is the EAP
   authenticator for PT-EAP.

1.4.  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].

1.5.  Compatibility with other Specifications

   One of the goals of the NEA effort is to deliver a single set of
   endpoint assessment standards, agreed upon by all parties.  For this
   reason, the Trusted Computing Group (TCG) will be replacing its
   existing posture transport protocols with new versions that are
   equivalent to and interoperable with the NEA specifications.


2.  Use of PT-EAP

   PT-EAP is designed to encapsulate PB-TNC batches in a simple EAP
   method that can be carried within EAP tunnel methods.  The EAP tunnel
   methods provide confidentiality and message integrity, so PT-EAP does
   not have to do so.  Therefore, PT-EAP MUST only be used inside an EAP
   tunnel method that provides strong cryptographic authentication
   (possibly server only), message integrity and confidentiality
   services.


3.  definition of PT-EAP

   The PT-EAP protocol operates between a Posture Transport Client and a
   Posture Transport Server, allowing them to send PB-TNC batches to
   each other over an EAP tunnel method.  When PT-EAP is used, the



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   Posture Transport Client in the NEA reference model acts as an EAP
   peer (terminating the PT-EAP method on the endpoint) and the Posture
   Transport Server acts as an EAP authenticator (terminating the PT-EAP
   method on the NEA Server).

   This section describes and defines the PT-EAP method.  First, it
   provides a protocol overview and a flow diagram.  Second, it
   describes specific features like version negotiation.  Third, it
   gives a detailed packet description.  Finally, it describes how the
   tls-unique channel binding [RFC5929] may be used to PA-TNC exchanges
   to the EAP tunnel method, defeating MITM attacks such as the Asokan
   attack [Asokan].

3.1.  Protocol Overview

   PT-EAP has two phases that follow each other in strict sequence:
   negotiation and data transport.

   The PT-EAP method begins with the negotiation phase.  The NEA Server
   starts this phase by sending an PT-EAP Start message: an EAP Request
   message of type PT-EAP with the S (Start) flag set.  The NEA Server
   also sets the Version field as described in Section 3.2.  This is the
   only message in the negotiation phase.

   The data transport phase is the only phase of PT-EAP where PB-TNC
   batches are allowed to be exchanged.  This phase always starts with
   the NEA Client sending a PB-TNC batch to the NEA Server.  The NEA
   Client and NEA Server then engage in a round-robin exchange with one
   PB-TNC batch in flight at a time.  The data transport phase always
   ends with an EAP Response message from the NEA Client to the NEA
   Server.  This message may be empty (not contain any data) if the NEA
   Server has just sent the last PB-TNC batch in the PB-TNC exchange.

   At the end of the PT-EAP method, the NEA Server will indicate success
   or failure to the EAP tunnel method.  Some EAP tunnel methods may
   provide explicit confirmation of inner method success; others may
   not.  This is out of scope for the PT-EAP method specification.
   Successful completion of PT-EAP does not imply successful completion
   of the overall authentication nor does PT-EAP failure imply overall
   failure.  This depends on the administrative policy in place.

   The NEA Server and NEA Client may engage in an abnormal termination
   of the PT-EAP exchange at any time by simply stopping the exchange.
   This may also require terminating the EAP tunnel method, depending on
   the capabilities of the EAP tunnel method.

   The NEA Server and NEA Client MUST follow the protocol sequence
   described in this section.



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3.2.  Version Negotiation

   PT-EAP version negotiation takes place in the first PT-EAP message
   sent by the NEA Server (the Start message) and the first PT-EAP
   message sent by the NEA Client (the response to the Start message).
   The NEA Server MUST set the Version field in the Start message to the
   maximum PT-EAP version that the NEA Server supports and is willing to
   accept.

   The NEA Client chooses the PT-EAP version to be used for the exchange
   and places this value in the Version field in its response to the
   Start message.  The NEA Client SHOULD choose the value sent by the
   NEA Server if the NEA Client supports it.  However, the NEA Client
   MAY set the Version field to a value less than the value sent by the
   NEA Server (for example, if the NEA Client only supports lesser PT-
   EAP versions).  If the NEA Client only supports PT-EAP versions
   greater than the value sent by the NEA Server, the EAP client MUST
   abnormally terminate the EAP negotiation.

   If the version sent by the NEA Client is not acceptable to the NEA
   Server, the NEA Server MUST terminate the PT-EAP session immediately.
   Otherwise, the version sent by the NEA Client is the version of PT-
   EAP that MUST be used.  Both the NEA Client and the NEA Server MUST
   set the Version field to the chosen version number in all subsequent
   PT-EAP messages in this exchange.

   This specification defines version 1 of PT-EAP.  Version 0 is
   reserved and MUST never be sent.  New versions of PT-EAP (values 2-7)
   may be defined by Standards Action, as defined in [RFC5226].

3.3.  PT-EAP Message Format

   This section provides a detailed description of the fields in an PT-
   EAP message.  For a description of the diagram conventions used here,
   see Section 1.2.  Since PT-EAP is an EAP method, the first four
   fields in each message are mandated by and defined in EAP.

     0                   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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Code      |   Identifier  |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Type       |   Flags | Ver |     Data Length               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Data Length           |           Data ...            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   Code

      The Code field is one octet and identifies the type of the EAP
      message.  The only values used for PT-EAP are:


   1  Request

   2  Response


   Identifier

      The Identifier field is one octet and aids in matching Responses
      with Requests.


   Length

      The Length field is two octets and indicates the length in octets
      of this PT-EAP message, starting from the Code field.


   Type

      TBD

   Flags



                            +-+-+-+-+-+
                            |L S R R R|
                            +-+-+-+-+-+


   L: Length included

      Indicates the presence of the Data Length field in the PT-EAP
      message.  This flag MUST be set for an PT-EAP message that
      contains Data (messages).


   S: Start

      Indicates the beginning of an PT-EAP exchange.  This flag MUST be
      set only for the first message from the NEA Server.  If the S flag
      is set, the EAP message MUST NOT contain Data or have the L flag



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      set.


   R: Reserved

      This flag MUST be set to 0 and ignored upon receipt.


   Version

      This field is used for version negotiation, as described in
      Section 3.2.


   Data Length

      The Data Length field MUST be set in the PT-EAP message if and
      only if the L flag is set.


   Data

      Variable length data.  The length of the Data field in a
      particular PT-EAP message may be determined by subtracting the
      length of the PT-EAP header fields from the value of the two octet
      Length field.

3.4.  Preventing MITM Attacks with Channel Bindings

   As described in the NEA Asokan Attack Analysis [16], a sophisticated
   MITM attack can be mounted against NEA systems.  The attacker
   forwards PA-TNC messages from a healthy machine through an unhealthy
   one so that the unhealthy machine can gain network access.  Because
   there are easier attacks on NEA systems, like having the unhealthy
   machine lie about its configuration, this attack is generally only
   mounted against machines with an External Measurement Agent (EMA).
   The EMA is a separate entity, difficult to compromise, which measures
   and attests to the configuration of the endpoint.

   To protect against NEA Asokan attacks, it is necessary for the
   Posture Broker on an EMA-equipped endpoint to pass the tls-unique
   channel binding [RFC5929] for PT-EAP's tunnel method to the EMA.
   This value can then be included in the EMA's attestation so that the
   Posture Validator responsible may then confirm that the value matches
   the tls-unique channel binding for its end of the tunnel.  If the
   tls-unique values between the NEA Client and NEA Server match
   endpoint, then the posture sent by the EMA (and thus the NEA Client)
   is from the same endpoint as the client side of the TLS connection



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   (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 and the Posture Validator SHOULD fail its verification.


4.  Security Considerations

   This section discusses the major threats and countermeasures provided
   by PT-EAP.  As discussed throughout the document, the PT-EAP method
   is designed to run inside an EAP tunnel method which is capable of
   protecting the PT-EAP protocol from many threats.  Since the EAP
   tunnel method will be specified separately, these security
   considerations specify requirements on the tunnel method but do not
   evaluate its ability to meet those requirements.  The security
   considerations and requirements for the NEA can be found in
   [RFC5209].

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-EAP 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-EAP protocol flowing
   inside an EAP tunnel.

4.1.1.  Posture Transport Client

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

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

   o  Not to 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




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   o  Expose the authenticated identity of the Posture Transport 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 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 to intentionally send malformed messages to cause processing
      problems for the Posture Transport Server

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

   o  Not to ignore or drop messages causing issues for the protocol
      processing

   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 to observe, fabricate or alter the contents of the PB-TNC
      batches received from the network

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

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

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

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



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   o  Expose the authenticated identity of the Posture Transport Client

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

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

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

   o  Not to send malformed messages

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

   o  Not to ignore or drop messages causing issues for the protocol
      processing

   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-EAP
   EAP method faces a number of potential security attacks that could
   require security countermeasures.

   Generally, the PT protocol is responsible for providing strong
   security protections for all of the NEA protocols so any threats to
   PT's ability to protect NEA protocol messages could be very damaging
   to deployments.  For the PT-EAP method, most of the cryptographic
   security is provided by the outer EAP tunnel method and PT-EAP is
   encapsulated within the protected tunnel.  Therefore, this section
   highlights the cryptographic requirements that need to be met by the
   EAP tunnel method carrying PT-EAP in order to meet the NEA PT
   requirements.

   Once the message is delivered to the Posture Broker Client or Posture
   Broker Server, the posture brokers are trusted to properly safely
   process the messages.

4.2.1.  Message Theft

   When PT-EAP messages are sent over unprotected network links or
   spanning local software stacks that are not trusted, the contents of



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   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-EAP is housed in an EAP tunnel
   method that does not provide confidentiality protection, an adversary
   could observe the PA-TNC attributes included in the PB-TNC batch 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 EAP
   tunnel method carrying PT-EAP MUST provide strong cryptographic
   authentication, integrity and confidentiality protection.  The use of
   bi-directional authentication in the EAP tunnel method carrying PT-
   EAP ensures that only properly authenticated and authorized parties
   may be involved in an assessment message exchange.  When PT-EAP is
   carried within a cryptographically protected EAP tunnel method like
   EAP-TTLS, all of the PB-TNC and PA-TNC protocol messages contents are
   hidden from potential theft by intermediaries lurking on the network.

4.2.2.  Message Fabrication

   Attackers on the network or present within the NEA system could
   introduce fabricated PT-EAP 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-
   EAP error codes in order to disrupt communications.

   The EAP tunnel method carrying an PT-EAP method needs to provide
   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.  For example,
   the EAP-TTLS method's use of hashing algorithms provides strong
   integrity protections that allow for detection of any changes in the
   content of the message exchange.  Adversaries are unable to observe
   the PT-EAP method housed inside of an encrypted EAP tunnel method
   (e.g.  EAP-TTLS) because the messages are encrypted by the TLS
   [RFC5246] ciphers.  Similarly, an attacker would have difficulty
   determining where to insert the falsified message since the attacker
   is unable to determine where the message boundaries exist.






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4.2.3.  Message Modification

   This attack could allow an active attacker capable of intercepting a
   message to modify a PT-EAP 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-EAP method leverages the EAP tunnel method (e.g.  EAP-TTLS) to
   provide strong authentication and integrity protections as a
   countermeasure to this threat.  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 (hashing) offered by EAP-TTLS allows the
   PT-EAP message recipients to detect message alterations by other
   types of network based adversaries.  Because PT-EAP does not itself
   provide explicit integrity protection for the PT-EAP payload, an EAP
   tunnel method that offers strong integrity protection is required to
   mitigate this threat.

4.2.4.  Denial of Service

   A variety of types of denial of service attacks are possible against
   the PT-EAP if the message exchange 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-EAP method primarily relies on the outer EAP tunnel method to
   provide strong authentication (at least of one party) and deployers
   are expected to leverage other EAP methods to authenticate the other
   party (typically the client) within the protected tunnel.  The use of
   a protected bi-directional authentication will prevent unauthorized
   parties from participating in a PT-EAP exchange.

   After the cryptographic authentication by the EAP tunnel method, the
   session can be encrypted and hashed to prevent 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.

4.2.5.  NEA Asokan Attacks

   As described in Section 3.4. and in the NEA Asokan Attack Analysis
   [Asokan], a sophisticated MITM attack can be mounted against NEA



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   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 3.4 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-EAP implementers may not know whether an
   EMA will be used with their implementation.  Therefore, PT-EAP
   implementers SHOULD support these 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.

4.3.  Requirements for EAP Tunnel Methods

   Because the PT-EAP inner method described in this specification
   relies on the outer EAP tunnel method for a majority of its security
   protections, this section reiterates the PT requirements that MUST be
   met by the IETF standard EAP tunnel method for use with PT-EAP.

   The security requirements described in this specification MUST be
   implemented in any product claiming to be PT-EAP compliant.  The
   decision of whether a particular deployment chooses to use these
   protections is a deployment issue.  A customer may choose to avoid
   potential deployment issues or performance penalties associated with
   the use of cryptography when the required protection has been
   achieved through other mechanisms (e.g. physical isolation).  If
   security mechanisms may be deactivated by policy, an implementation
   SHOULD offer an interface to query how a message will be (or was)
   protected by PT so higher layer NEA protocols can factor this into
   their decisions.

   RFC 5209 [RFC5209] includes the following requirement that is to be
   applied during the selection of the EAP tunnel method(s) used in
   conjunction with PT-EAP:

      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.

   Note that mutual authentication could be achieved by a combination of
   a strong authentication of one party (e.g.  TLS server when EAP-TTLS
   is used) by the EAP tunnel method in conjunction with a second



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   authentication of the other party (e.g. client authentication inside
   the protected tunnel) by another EAP method running prior to PT-EAP.

   Having the Posture Transport Client always authenticate the Posture
   Transport Server provides assurance to the NEA Client that the NEA
   Server is authentic (not a rogue or MiTM) prior to disclosing secret
   or potentially privacy sensitive information about what is running or
   configured on the endpoint.  However the NEA Server's policy may
   allow for the delay of the authentication of the NEA Client until a
   suitable protected channel has been established allowing for non-
   cryptographic NEA Client credentials (e.g. username/password) to be
   used.  Whether the communication channel is established with mutual
   or server-side only authentication, the resulting channel needs to
   provide strong integrity and confidentiality protection to its
   contents.  These protections are to be bound to at least the
   authentication of the NEA Server by the NEA Client, so the session is
   cryptographically bound to a particular authentication event.

   To support countermeasures against NEA Asokan attacks as described in
   Section 3.4. the EAP Tunnel Method used with PT-EAP will need to
   support the tls-unique channel binding.  This should not be a high
   bar since all EAP tunnel methods currently support this but not all
   implementations of those methods may do so.

4.4.  Candidate EAP Tunnel Method Protections

   This section discusses how PT-EAP is used within various EAP tunnel
   methods to meet the PT requirements from section Section 4.3.

   EAP-FAST [RFC4851] and EAP-TTLS [RFC5281]make use of TLS [RFC5246] to
   protect the transport of information between the NEA Client and NEA
   Server.  Each of these EAP tunnel methods has two phases.  In the
   first phase, a TLS tunnel is established between NEA Client and NEA
   Server.  In the second phase, the tunnel is used to pass other
   information.  PT-EAP requires that establishing this tunnel include
   at least an authentication of the NEA Server by the NEA Client.

   The phase two dialog may include authentication of the user by doing
   other EAP methods or in the case of TTLS by using non-EAP
   authentication dialogs.  PT-EAP is also carried by the phase two
   tunnel allowing the NEA assessment to be within an encrypted and
   integrity protected transport.

   With all these methods (e.g.  EAP-FAST [RFC4851] and EAP-TTLS
   [RFC5281], a cryptographic key is derived from the authentication
   that may be used to secure later transmissions.  Each of these
   methods employs at least a NEA Server authentication using an X.509
   certificate.  Within each EAP tunnel method will exist a set of inner



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   EAP method (or an equivalent using TLVs if inner methods aren't
   directly supported.)  These inner methods may perform additional
   security handshakes including more granular authentications or
   exchanges of integrity information (such as PT-EAP.)  At some point
   after the conclusion of each inner EAP method, some of the methods
   will export the established secret keys to the outer tunnel method.
   It's expected that the outer method will cryptographically mix these
   keys into any keys it is currently using to protect the session and
   perform a final operation to determine whether both parties have
   arrived at the same mixed key.  This cryptographic binding of the
   inner method results to the outer methods keys is essential for
   detection of conventional (non-NEA) Asokan attacks.

4.5.  Security Claims for PT-EAP as per RFC3748

   This section summarizes the security claims, for this specification,
   as required by RFC3748 Section 7.2:

            Auth. mechanism:       None
            Ciphersuite negotiation:       No
            Mutual authentication: No
            Integrity protection:  No
            Replay protection:     No
            Confidentiality:       No
            Key derivation:        No
            Key strength:  N/A
            Dictionary attack resistant:   N/A
            Fast reconnect:        No
            Crypt. binding:        N/A
            Session independence:  N/A
            Fragmentation: Yes
            Channel binding:       No


5.  Privacy Considerations

   The role of PT-EAP is to act as a secure transport for PB-TNC over a
   network before the endpoint has been admitted to the network.  As a
   transport protocol, PT-EAP does not directly utilize or require
   direct knowledge of any personally identifiable information (PII).
   PT-EAP will typically be used in conjunction with other EAP methods
   that provide for the user authentication (if bi-directional
   authentication is used), so the user's credentials are not directly
   seen by the PT-EAP inner method.  Therefore, the Posture Transport
   Client and Posture Transport Server's implementation of PT-EAP MUST
   NOT observe the contents of the carried PB-TNC batches that could
   contain PII carried by PA-TNC or PB-TNC.




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   While PT-EAP does not provide cryptographic protection for the PB-TNC
   batches, it is designed to operate within an EAP tunnel method that
   provides strong authentication, integrity and confidentiality
   services.  Therefore, it is important for deployers to leverage these
   protections in order to prevent disclosure of PII potentially
   contained within PA-TNC or PB-TNC within the PT-EAP payload.


6.  IANA Considerations

   This section provides guidance to the Internet Assigned numbers
   Authority (IANA) regarding registration of values related to the PT-
   EAP protocol, in accordance with BCP 26 [RFC2434]

   The EAP Method type for PT-EAP needs to be assigned.

   This document also defines one new IANA registry: PT-EAP Versions.
   This section explains how this registry works.  Because only eight
   (8) values are available in this registry, a high bar is set for new
   assignments.  The only way to register new values in this registry is
   through Standards Action (via an approved Standards Track RFC).

6.1.  Registry for PT-EAP Versions

   The name for this registry is "PT-EAP Versions".  Each entry in this
   registry includes a decimal integer value between 1 and 7 identifying
   the version, and a reference to the RFC where the version is defined.

   The following entries for this registry are defined in this document.
   Once this document becomes an RFC, they will become the initial
   entries in the registry for PT-EAP Versions.  Additional entries to
   this registry are added by Standards Action, as defined in RFC 5226
   [RFC5226].

                  +-------+----------------------------+
                  | Value |   Defining Specification   |
                  +-------+----------------------------+
                  |   1   | RFC # Assigned to this I-D |
                  +-------+----------------------------+


7.  Acknowledgements

   Thanks to the Trusted Computing Group for contributing the initial
   text upon which this document was based.

   The authors of this draft would like to acknowledge the following
   people who have contributed to or provided substantial input on the



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   preparation of this document or predecessors to it: Amit Agarwal,
   Morteza Ansari, Diana Arroyo, Stuart Bailey, Boris Balacheff, Uri
   Blumenthal, Gene Chang, Scott Cochrane, Pasi Eronen, Aman Garg,
   Sandilya Garimella, David Grawrock, Thomas Hardjono, Chris Hessing,
   Ryan Hurst, Hidenobu Ito, John Jerrim, Meenakshi Kaushik, Greg
   Kazmierczak, Scott Kelly, Bryan Kingsford, PJ Kirner, Sung Lee, Lisa
   Lorenzin, Mahalingam Mani, Bipin Mistry, Seiji Munetoh, Rod
   Murchison, Barbara Nelson, Kazuaki Nimura, Ron Pon, Ivan Pulleyn,
   Alex Romanyuk, Ravi Sahita, Chris Salter, Mauricio Sanchez, Paul
   Sangster, Dean Sheffield, Curtis Simonson, Jeff Six, Ned Smith,
   Michelle Sommerstad, Joseph Tardo, Lee Terrell, Chris Trytten, and
   John Vollbrecht.

   This document was prepared using template-bare-05.xml.


8.  References

8.1.  Normative References

   [IEEE]     IEEE Std. 802.1X-2004, "LAN/MAN Standards Committee of the
              IEEE Computer Society, Standard for Local and
              Metrolpolitan Area Network - Port Based Network Access
              Control", December 2004, <http://standards.ieee.org/
              getieee802/download/802.1X-2010.pdf>.

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

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

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

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

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

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




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

8.2.  Informative References

   [Asokan]   Asokan, N., Niemi, V., Nyberg, K., and Nokia Research
              Center, Finland, ""Man in the Middle Attacks in Tunneled
              Authentication Protocols"", Nov 2002,
              <http://eprint.iacr.org/2002/163.pdf>.

   [I-D.ietf-emu-eaptunnel-req]
              Zhou, H., Salowey, J., Hoeper, K., and S. Hanna,
              "Requirements for a Tunnel Based EAP Method",
              draft-ietf-emu-eaptunnel-req-09 (work in progress),
              December 2010.

   [I-D.ietf-nea-pt-tls]
              Sangster, P., Cam-Winget, N., and J. Salowey, "PT-TLS: A
              TCP-based Posture Transport (PT) Protocol",
              draft-ietf-nea-pt-tls-02 (work in progress), March 2012.

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

   [RFC3478]  Leelanivas, M., Rekhter, Y., and R. Aggarwal, "Graceful
              Restart Mechanism for Label Distribution Protocol",
              RFC 3478, February 2003.

   [RFC4851]  Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "The
              Flexible Authentication via Secure Tunneling Extensible
              Authentication Protocol Method (EAP-FAST)", RFC 4851,
              May 2007.

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

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, March 2008.

   [RFC5281]  Funk, P. and S. Blake-Wilson, "Extensible Authentication
              Protocol Tunneled Transport Layer Security Authenticated
              Protocol Version 0 (EAP-TTLSv0)", RFC 5281, August 2008.

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings



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              for TLS", RFC 5929, July 2010.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

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


Authors' Addresses

   Nancy Cam-Winget (editor)
   Cisco Systems
   80 West Tasman Drive
   San Jose, CA  95134

   Email: ncamwing@cisco.com


   Paul Sangster (editor)
   Symantec Corporation
   6825 Citrine Drive
   Carlsbad, CA  92009
   USA

   Email: paul_sangster@symantec.com





















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