NETWORK WORKING GROUP N. Williams Internet-Draft Sun Expires: September 6, 2007 March 5, 2007 On the Use of Channel Bindings to Secure Channels draft-williams-on-channel-binding-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 6, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Williams Expires September 6, 2007 [Page 1] Internet-Draft On Channel Bindings March 2007 Abstract The concept of channel binding allows applications to establish that the two end-points of a secure channel at one network layer are the same as at a higher layer by binding authentication at the higher layer to the channel at the lower layer. This allows applications to delegate session protection to lower layers, which has various performance benefits. This document discusses and formalizes the concept of channel binding to secure channels. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . 4 2. Definitions . . . . . . . . . . . . . . . . . . . . . 5 2.1. Properties of channel binding . . . . . . . . . . . . 6 3. Authentication and channel binding semantics . . . . . 9 3.1. The GSS-API and channel binding . . . . . . . . . . . 9 3.2. SASL and channel binding . . . . . . . . . . . . . . . 9 4. Channel bindings specifications . . . . . . . . . . . 11 4.1. Examples of unique channel bindings . . . . . . . . . 11 4.2. Examples of end-point channel bindings . . . . . . . . 11 5. Uses of channel binding . . . . . . . . . . . . . . . 13 6. Benefits of channel binding to secure channels . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . 16 8. Security Considerations . . . . . . . . . . . . . . . 17 8.1. Non-unique channel bindings and channel binding re-establishment . . . . . . . . . . . . . . . . . . . 17 9. References . . . . . . . . . . . . . . . . . . . . . . 19 9.1. Normative References . . . . . . . . . . . . . . . . . 19 9.2. Informative References . . . . . . . . . . . . . . . . 19 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 22 Author's Address . . . . . . . . . . . . . . . . . . . 23 Intellectual Property and Copyright Statements . . . . 24 Williams Expires September 6, 2007 [Page 2] Internet-Draft On Channel Bindings March 2007 1. Introduction In a number of situations, it is useful for an application to be able to handle authentication within the application layer, while simultaneously being able to utilize session or transport security at a lower network layer. For example, while IPsec [RFC4301] [RFC4303] [RFC4302] is amenable to being accelerated in hardware to handle very high link speeds, but IPsec key exchange protocols and the IPsec architecture are not as amenable to use as a security mechanism within applications, particularly applications that have users as clients. A method of combining security at both layers is therefore attractive. To enable this to be done securely, it is necessary to "bind" the mechanisms together -- so as to avoid man-in-the-middle vulnerabilities and enable the mechanisms to be integrated in a seamless way. This is the objective of "Channel Bindings." The term "channel binding" as used in this document derives from the GSS-API [RFC2743], which has a channel binding facility that was intended for binding GSS-API authentication to secure channels at lower network layers. The purpose and benefits of the GSS-API channel binding facility were not discussed at length, and some details were left unspecified. Now we find that this concept can be very useful, therefore we begin with a generalization and formalization of "channel binding." The main goal of channel binding is to be able to delegate cryptographic session protection to network layers below the application in hopes of being able to better leverage hardware implementations of cryptographic protocols. Section 5 describes some intended uses of channel binding. Some applications may benefit additionally by reducing the amount of active cryptographic state, thus reducing overhead in accessing such state and, therefore, the impact of security on latency. The critical security problem to solve in order to achieve such delegation of session protection is: ensuring that there is no man- in-the-middle (MITM), from the point of view the application, at the lower network layer to which session protection is to be delegated. And there may well be a MITM, particularly if the lower network layer either provides no authentication or if there is no strong connection between the authentication or principals used at the application and those used at the lower network layer. Even if such MITM attacks seem particularly difficult to effect, the attacks must be prevented for certain applications to be able to make effective use of technologies such as IPsec [RFC2401] [RFC4301] or HTTP with TLS [RFC4346] in certain contexts (e.g., when there is no Williams Expires September 6, 2007 [Page 3] Internet-Draft On Channel Bindings March 2007 authentication to speak of, or when one node's set of trust anchors is too weak to believe that it can authenticate its peers). Additionally, secure channels that are susceptible to MITM attacks because they provide no useful end-point authentication are useful when combined with application-layer authentication (otherwise they are only somewhat "better than nothing" -- see BTNS [I-D.ietf-btns-prob-and-applic]). For example, iSCSI [RFC3720] provides for application-layer authentication (e.g., using Kerberos V), but relies on IPsec for transport protection; iSCSI does not provide a binding between the two. iSCSI initiators have to be careful to make sure that the name of the server authenticated at the application layer and the name of the peer at the IPsec layer match -- an informal form of channel binding. This document describes a solution: the use of "channel binding" (in the GSS-API [RFC2743] [RFC2744] sense) to bind authentication at application layers to secure sessions at lower layers in the network stack. 1.1. 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 [RFC2119]. Williams Expires September 6, 2007 [Page 4] Internet-Draft On Channel Bindings March 2007 2. Definitions o Secure channel: a packet, datagram, octet stream connection, or sequence of connections, between two end-points that affords cryptographic integrity and, optionally, confidentiality to data exchanged over it. We assume that the channel is secure -- if an attacker can successfully cryptanalyze a channel's session keys, for example, then the channel is not secure. o Channel binding: the process of establishing that no man-in-the- middle exists between two end-points authenticated at one network layer but using a secure channel at a lower network layer. This term is used as a noun. o Channel bindings: [See historical note below.] Generally some data which "names" a channel or one or both of its end-points such that if this data can be shown, at a higher network layer, to be the same at both ends of a channel then there are no MITMs between the two end-points at that higher network layer. This term is used as a noun. More formally, there are two types of channel bindings: + unique channel bindings: channel bindings that name a channel in a cryptographically secure manner and uniquely in time; + end-point channel bindings: channel bindings that name the authenticated end-points, or even a single end-point, of a channel which are, in turn, securely bound to the channel, but which do not identify a channel uniquely in time. o Cryptographic binding: (e.g., "cryptographically bound") a cryptographic operation that causes an object, such as a private encryption or signing key, or an established secure channel, to "speak for" [Lapmson91] some principal, such as a user, a computer, etcetera. For example, a PKIX certificate binds a private key to the name of a principal in the trust domain of the certificate's issuer such that a possessor of said private key can act on behalf of the user (or other entity) named by the certificate. Williams Expires September 6, 2007 [Page 5] Internet-Draft On Channel Bindings March 2007 Cryptographic bindings are generally assymetric in nature (not to be confused with symmetric or assymetric key cryptography) in that an object is rendered capable of standing for another, but the reverse is not usually the case (we don't say that a user speaks for their private keys, but we do say that the user's private keys speak for the user). Note that there may be many instances of "cryptographic binding" in an application of channel binding. The credentials that authenticate principals at the application layer bind private or secret keys to the identities of those principals, such that said keys speak for them. A secure channel typically consists symmetric session keys used to provide confidentiality and integrity ptoection to data sent over the channel; each end-point's session keys speak for that end- point of the channel. Finally, each end-point of a channel bound to authentication at the application layer speaks for the principal authenticated at the application layer on the same side of the channel. The terms defined above have been in use for many years and have been taken to mean, at least in some contexts, what is stated below. Unfortunately this means that "channel binding" can refer to the channel binding operation and, sometimes to the name of a channel, and "channel bindings" -- a difference of only one letter -- generally refers to the name of a channel. Also unfortunately there is a conflict with the Extensible Authentication Protocol (EAP) [RFC3748] which uses "channel binding" to refer to a facility that is subtly different from the one described here. (It does not seem feasible to adopt new terminology to avoid these problems now. The GSS-API, NFSv4 and other communities have been using the terms "channel binding" and "channel bindings" in these ways for a long time, sometimes with variations such as "channel binding facility" and so on.) 2.1. Properties of channel binding [NOTE: This section needs more work, I'm sure I've missed somethings...] Applications, authentication frameworks (e.g., the GSS-API, SASL), security mechanisms (e.g., the Kerberos V GSS-API mechanism [RFC1964]) and secure channels must meet the following requirement and should follow the following recommendations. Requirements: Williams Expires September 6, 2007 [Page 6] Internet-Draft On Channel Bindings March 2007 o Specifications of channel bindings for any secure channels MUST provide for a single, canonical octet string encoding of the channel bindings. o The channel bindings for a given type of secure channel MUST be constructed in such a way that an MITM could not easily force the channel bindings of a given channel to match those of another. o Unique channel bindings MUST bind not only the key exchange for the secure channel, but also any negotiations and authentication that may have taken place to establish the channel. o End-point channel bindings MUST be bound into the secure channel and all its negotiations. E.g., if an end-point channel binding is the name of a certificate and this certificate is used in establishng the channel to sign material, say, all the initinial key exchange and negotiation messages for that channel, then that certificate name could be said to be bound into the channel. o End-point channel bindings may be identifiers which must be authenticated through some infrastructure, such as a public key infrastructure (PKI). In such cases the channel binding can be no stronger, cryptographically, than the infrastructure, including trust establishment. Applications MUST NOT use end-point channel bindings when the end-points cannot be strongly authenticated due to the configuration of the authentication service (e.g., because there are too many trust anchors, or because some are of dubious repute). o Applications MUST use application-layer session protection services for confidentiality protection when the bound channel does not provide confidentiality protection. o The integrity of a secure channels MUST NOT be weakened should their channel bindings be revealed to an attacker. That is, the construction of the channel bindings for any type of secure channel MUST NOT leak secret information about the channel. End- point channel bindings, however, MAY leak information about the end-points of the channel (e.g., their names). o The channel binding operation MUST be at least integrity protected in the security mechanism used at the application layer. o Authentication frameworks and mechanisms that support channel binding MUST communicate channel binding failure to applications. Recommendations: Williams Expires September 6, 2007 [Page 7] Internet-Draft On Channel Bindings March 2007 o Applications SHOULD use mutual authentication at the application layer when using channel binding. o End-point channel bindings where the end-points are meaningful names SHOULD NOT be used when the channel does not provide confidentiality protection and privacy protection is desired. Alternatively channels that export such channel bindings SHOULD provide for the use of a digest and SHOULD NOT introduce new digest/hash agility problems as a result. Options: o Authentication frameworks and mechanisms that support channel binding MAY fail to establish authentication if channel binding fails. o A security mechanism MAY exchange integrity protected channel bindings. o A security mechanism MAY exchange integrity protected digests of channel bindings. Such mechanisms SHOULD provide for hash/digest agility. o A security mechanism MAY use channel bindings in key exchange, authentication or key derivation, prior to the exchange of "authenticator" messages. Williams Expires September 6, 2007 [Page 8] Internet-Draft On Channel Bindings March 2007 3. Authentication and channel binding semantics Some authentication frameworks and/or mechanisms provide for channel binding, such as the GSS-API and some GSS-API mechanisms, whereas others may not, such as SASL (however, ongoing work is adding channel binding support to SASL). Semantics may vary with respect to negotiation, how the binding occurs, and handling of channel binding failure (see below). Where suitable channel binding facilities are not provided, application protocols MAY include a separate, protected exchange of channel bindings. In order to do this the application-layer authentication service must provide message protection services, at least integrity protection. 3.1. The GSS-API and channel binding The GSS-API [RFC2743] provides for the use of channel binding during initialization of GSS-API security contexts, though GSS-API mechanisms are not required to support this facility. This channel binding facility is described in [RFC2743] and [RFC2744]. GSS-API mechanisms must fail security context establishment when channel binding fails, and the GSS-API provides no mechanism for the negotiation of channel binding. As a result GSS-API applications must agree a priori, through negotiation or otherwise, on the use of channel binding. Fortunately, it is possible to design GSS-API pseudo-mechanisms that simply wrap around existing mechanisms for the purpose of allowing applications to negotiate the use of channel binding within their existing methods for negotiating GSS-API mechanisms. For example, NFSv4 [RFC3530] provides its own GSS-API mechanism negotiation, as does the SSHv2 protocol [RFC4462]. Such pseudo-mechanisms are being proposed separately, see [I-D.ietf-kitten-stackable-pseudo-mechs]. 3.2. SASL and channel binding SASL [RFC4422] does not yet provide for the use of channel binding during initialization of SASL contexts. Work is ongoing [I-D.ietf-sasl-gs2] to specify how SASL, particularly it's new bridge to the GSS-API, performs channel binding. SASL will likely differ from the GSS-API in its handling of channel binding failure (i.e., when there may be a MITM) in that channel binding success/failure will only affect the negotiation of SASL security Williams Expires September 6, 2007 [Page 9] Internet-Draft On Channel Bindings March 2007 layers. I.e., when channel binding succeeds SASL should select no security layers, leaving session cryptographic protection to the secure channel that has been bound to. Williams Expires September 6, 2007 [Page 10] Internet-Draft On Channel Bindings March 2007 4. Channel bindings specifications Channel bindings for various types of secure channels are not described herein. Some channel bindings specifications can be found in: +--------------------+----------------------------------------------+ | Secure Channel | Reference | | Type | | +--------------------+----------------------------------------------+ | SSHv2 | [I-D.williams-sshv2-channel-bindings] | | | | | TLS | [I-D.altman-tls-channel-bindings] | | | | | IPsec | There is no specification for this yet. We | | | expect that channel bindings for IPsec will | | | be of the non-unique variety. | +--------------------+----------------------------------------------+ 4.1. Examples of unique channel bindings The following text is not normative, but is here to show how one might construct channel bindings for various types of secure channels. For SSHv2 [RFC4251] the SSHv2 session ID should suffice as it is a cryptographic binding of all relevant SSHv2 connection parameters: key exchange and negotiation. For TLS [RFC4346]the TLS session ID is not sufficient as it is assigned by the server, and so could be assigned by an MITM to match a server's. Instead the initial, unencrypted TLS finished messages, either the client's, the server's or both, are sufficient as they are the output of the TLS PRF, keyed with the session key, applied to all handshake material. 4.2. Examples of end-point channel bindings The following text is not normative, but is here to show how one might construct channel bindings for various types of secure channels. For SSHv2 [RFC4251] the SSHv2 host public key, when present, should suffice as it is used to sign the algorithm suite negotiation and Diffie-Hellman key exchange; as long the client observes the host public key that corresponds to the private host key that the server used then there cannot be a MITM in the SSHv2 connection. Note that not all SSHv2 key exchanges use host public keys, therefore this Williams Expires September 6, 2007 [Page 11] Internet-Draft On Channel Bindings March 2007 channel bindings construction is not as useful as the one given in Section 4.1 above. For TLS [RFC4346]the server certificate should suffice for the same reasons as above. Again, not all TLS cipher suites involve server certificates, therfore the utility of this construction of channel bindings is limited to scenarios where server certificates are commonly used. Williams Expires September 6, 2007 [Page 12] Internet-Draft On Channel Bindings March 2007 5. Uses of channel binding Uses for channel binding identified so far: o Delegating session cryptographic protection to layers where hardware can reasonably be expected to support relevant cryptographic protocols: * NFSv4 [RFC3530] with Remote Direct Data Placement (RDDP) [I-D.ietf-nfsv4-nfsdirect] for zer-copy reception where network interface controllers (NICs) support RDDP. Cryptographic session protection would be delegated to ESP/AH [RFC4303] [RFC4302]. * iSCSI [RFC3720] with Remote Direct Memory Access (RDMA) [I-D.ietf-ips-iser]. Cryptographic session protection would be delegated to ESP/AH. * HTTP with TLS [RFC2817] [RFC2818]. In situations involving proxies users may want to bind authentication to a TLS channel between the last client-side proxy and the first server-side proxy ("concentrator"). There is ongoing work to expand the set of choices for end-to-end authentication at the HTTP layer, which coupled with channel binding to TLS would allow for proxies while not forgoing protection over public internets. o Reducing the number of live cryptographic contexts that an application must maintain: * NFSv4 [RFC3530] multiplexes multiple users onto individual connections. Each user is authenticated separately and user's RPCs are protected with per-user GSS-API security contexts. This means that large timesharing clients must often maintain many cryptographic contexts per-NFSv4 conenction. With channel binding to IPsec they could maintain a much smaller number of cryptographic contexts per-NFSv4 connection, thus reducing memory pressure and interactions with cryptographic hardware. For example, applications that wish to use RDDP to achieve zero-copy semantics on reception may use a network layer understood by network interface controllers (NIC) to offload delivery of application data into pre-arranged memory buffers. Note that in order to obtain zero- copy reception semantics either application data has to be in cleartext relative to this RDDP layer, or the RDDP implementation must know how to implement cryptographic session protection protocols used at the application layer. There are a multitude of application layer cryptographic session Williams Expires September 6, 2007 [Page 13] Internet-Draft On Channel Bindings March 2007 protection protocols available. It is not reasonable to expect the NICs should support many such protocols. Further, some application protocols may maintain many cryptographic session contexts per- connection (for example, NFSv4 does). It is thought to be simpler to push the cryptographic session protection down the network stack, to IPsec, and yet be able to produce NICs that offload TCP/IP, ESP/AH, and DDP operations, than it would be to add support in the NIC for the many session cryptographic protection protocols in use in common applications at the application layer. The following figure shows how the various network layers are related: +---------------------+ | Application layer |<---+ | |<-+ | In cleartext, relative +---------------------+ | | to each other. | RDDP |<---+ +---------------------+ | | TCP/SCTP |<-+ +---------------------+ | Channel binding of app-layer | ESP/AH |<-+ authentication to IPsec +---------------------+ | IP | +---------------------+ | ... | +---------------------+ Williams Expires September 6, 2007 [Page 14] Internet-Draft On Channel Bindings March 2007 6. Benefits of channel binding to secure channels The use of channel binding to delegate session cryptographic protection include: o Performance improvements by avoiding double protection of application data in cases where IPsec is in use and applications provide their own secure channels. o Performance improvements by leveraging hardware-accelerated IPsec. o Performance improvements by allowing RDDP hardware offloading to be integrated with IPsec hardware acceleration. Where protocols layered above RDDP use privacy protection RDDP offload cannot be done, thus by using channel binding to IPsec the privacy protection is moved to IPsec, which is layered below RDDP, so RDDP can address application protocol data that's in cleartext relative to the RDDP headers. o Latency improvements for applications that multiplex multiple users onto a single channel, such as NFS w/ RPCSEC_GSS. Delegation of session cryptographic protection to IPsec requires features not yet specified. There is ongoing work to specify: o IPsec channels [I-D.ietf-btns-connection-latching]; o Application programming interfaces (APIs) related to IPsec channels [I-D.ietf-btns-ipsec-apireq]; o Channel bindings for IPsec channels; o Low infrastructure IPsec authentication[I-D.ietf-btns-core]. Williams Expires September 6, 2007 [Page 15] Internet-Draft On Channel Bindings March 2007 7. IANA Considerations There are no IANA considerations in this document. Williams Expires September 6, 2007 [Page 16] Internet-Draft On Channel Bindings March 2007 8. Security Considerations Security considerations appear throughout this document. In particular see Section 2.1. When delegating session protection from one layer to another, one will almost certainly be making some session security trade-offs, such as using weaker cipher modes in one layer than might be used in the other. Evaluation and comparison of the relative cryptographic strengths of these is difficult, may not be easily automated and is far out of scope for this document. Implementors and administrators should understand these trade-offs. Interfaces to secure channels and application-layer authentication frameworks and mechanisms could provide some notion of security profile so that applications may avoid delegation of session protection to channels that are too weak to match a required security profile. Channel binding makes "anonymous" channels (where neither end-point is strongly authenticated to the other) useful. Implementors should avoid making use of such channels without channel binding easy to configure accidentally. The security of channel binding depends on the security of the channels, the construction of their channel bindings, and the security of the authentication mechanism used by the application and its channel binding method. Channel bindings should be constructed in such a way that revealing the channel bindings of a channel to third parties does not weaken the security of the channel. However, for end-point channel bindings disclosure of the channel bindings may disclose the identities of the peers. 8.1. Non-unique channel bindings and channel binding re-establishment Applications developers may be tempted to use non-unique channel bindings for fast re-authentication following channel re- establishment. Care must be taken to avoid the possibility of attacks on multi-user systems. Consider a user multiplexing protocol like NFSv4 using channel binding to IPsec on a multi-user client. If another user can connect directly to port 2049 (NFS) on some server using IPsec and merely assert RPCSEC_GSS credential handles, then this user will be able to impersonate any user authenticated by the client to the server. This is because the new connection will have the same channel bindings as the NFS client's! To prevent this the server must require that at least a hostbased client principal, and perhaps all the client's user Williams Expires September 6, 2007 [Page 17] Internet-Draft On Channel Bindings March 2007 principals, re-authenticate and perform channel binding before the server will allow the clients to assert RPCSEC_GSS context handles. Alternatively the protocol could: a) require that secure channels provide confidentiality protection, and b) that fast re- authentication cookies be difficult to guess (e.g., large numbers selected randomly). In other contexts there may not be such problems, for example, in the case of application protocols that don't multiplex users over a single channel and where confidentiality protection is always used in the secure channel. Williams Expires September 6, 2007 [Page 18] Internet-Draft On Channel Bindings March 2007 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 9.2. Informative References [I-D.altman-tls-channel-bindings] Williams, N., "Channel Bindings for SSHv2", draft-altman-tls-channel-bindings-00 (work in progress), July 2006. [I-D.ietf-btns-connection-latching] Williams, N., "IPsec Channels: Connection Latching", draft-ietf-btns-connection-latching-00 (work in progress), February 2006. [I-D.ietf-btns-core] Richardson, M. and N. Williams, "Better-Than-Nothing- Security: An Unauthenticated Mode of IPsec", draft-ietf-btns-core-01 (work in progress), June 2006. [I-D.ietf-btns-ipsec-apireq] Richardson, M. and B. Sommerfeld, "Requirements for an IPsec API", draft-ietf-btns-ipsec-apireq-00 (work in progress), April 2006. [I-D.ietf-btns-prob-and-applic] Touch, J., "Problem and Applicability Statement for Better Than Nothing Security (BTNS)", draft-ietf-btns-prob-and-applic-05 (work in progress), February 2007. [I-D.ietf-ips-iser] Ko, M., "iSCSI Extensions for RDMA Specification", draft-ietf-ips-iser-06 (work in progress), October 2005. [I-D.ietf-kitten-stackable-pseudo-mechs] Williams, N., "Stackable Generic Security Service Pseudo- Mechanisms", draft-ietf-kitten-stackable-pseudo-mechs-02 (work in progress), June 2006. [I-D.ietf-nfsv4-nfsdirect] Callaghan, B. and T. Talpey, "NFS Direct Data Placement", draft-ietf-nfsv4-nfsdirect-04 (work in progress), October 2006. Williams Expires September 6, 2007 [Page 19] Internet-Draft On Channel Bindings March 2007 [I-D.ietf-sasl-gs2] Josefsson, S., "Using GSS-API Mechanisms in SASL: The GS2 Mechanism Family", draft-ietf-sasl-gs2-06 (work in progress), February 2007. [I-D.williams-sshv2-channel-bindings] Williams, N., "Channel Bindings for Secure Shell Channels", draft-williams-sshv2-channel-bindings-00 (work in progress), July 2006. [Lapmson91] Lampson, B., Abadi, M., Burrows, M., and E. Wobber, "Authentication in Distributed Systems: Theory and Practive", October 1991. [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1964, June 1996. [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [RFC2743] Linn, J., "Generic Security Service Application Program Interface Version 2, Update 1", RFC 2743, January 2000. [RFC2744] Wray, J., "Generic Security Service API Version 2 : C-bindings", RFC 2744, January 2000. [RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within HTTP/1.1", RFC 2817, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C., Eisler, M., and D. Noveck, "Network File System (NFS) version 4 Protocol", RFC 3530, April 2003. [RFC3720] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E. Zeidner, "Internet Small Computer Systems Interface (iSCSI)", RFC 3720, April 2004. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Williams Expires September 6, 2007 [Page 20] Internet-Draft On Channel Bindings March 2007 Internet Protocol", RFC 4301, December 2005. [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006. [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch, "Generic Security Service Application Program Interface (GSS-API) Authentication and Key Exchange for the Secure Shell (SSH) Protocol", RFC 4462, May 2006. Williams Expires September 6, 2007 [Page 21] Internet-Draft On Channel Bindings March 2007 Appendix A. Acknowledgments Thanks to Mike Eisler for his work on the Channel Conjunction Mechanism I-D and for bringing the problem to a head, Sam Hartman for pointing out that channel binding provide a general solution to the channel binding problem, Jeff Altman for his suggestion of using the TLS finished messages as the TLS channel bindings, Bill Sommerfeld, Radia Perlman, Simon Josefsson, Joe Salowey, Eric Rescorla, Michael Richardson, Bernard Aboba, Tom Petch, Mark Brown and many others. Williams Expires September 6, 2007 [Page 22] Internet-Draft On Channel Bindings March 2007 Author's Address Nicolas Williams Sun Microsystems 5300 Riata Trace Ct Austin, TX 78727 US Email: Nicolas.Williams@sun.com Williams Expires September 6, 2007 [Page 23] Internet-Draft On Channel Bindings March 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Williams Expires September 6, 2007 [Page 24]