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]