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NETWORK WORKING GROUP                                        N. Williams
Internet-Draft                                                       Sun
Intended status: Standards Track                          April 21, 2008
Expires: October 23, 2008

    End-Point Channel Bindings for IPsec Using IKEv2 and Public Keys

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

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   This document specifies the end-point channel bindings for "IPsec
   channels" where the peers used the Internet Key Exchange protocol
   version 2 (IKEv2) and where they used public keys and/or certificates
   to authenticate each other.  Specifically, we use hashes of the end-
   points' public keys.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  Conventions used in this document  . . . . . . . . . . . . .  3
   2.    IPsec Unique Channel Bindings  . . . . . . . . . . . . . . .  4
   2.1.  API Requirements . . . . . . . . . . . . . . . . . . . . . .  4
   3.    IANA Considerations  . . . . . . . . . . . . . . . . . . . .  5
   4.    Security Considerations  . . . . . . . . . . . . . . . . . .  6
   5.    References . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.1.  Normative References . . . . . . . . . . . . . . . . . . . .  7
   5.2.  Informative References . . . . . . . . . . . . . . . . . . .  7
         Author's Address . . . . . . . . . . . . . . . . . . . . . .  9
         Intellectual Property and Copyright Statements . . . . . . . 10

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1.  Introduction

   Given the ability to construct IPsec channels
   [I-D.ietf-btns-connection-latching] and the ability to bind
   authentication at application layers to such secure channels
   [RFC5056] the only missing components are: a definition of IPsec
   channel bindings, and Application Programming Interfaces (APIs) by
   which applications can obtain them.

   Here we specify the "end-point channel bindings" [RFC5056] for IPsec
   channels when peers use IKEv2 [RFC4306] and public keys and/or
   certificates [RFC3280].  IPsec APIs [I-D.ietf-btns-ipsec-apireq] are
   out of scope for this document, but some requirements for such APIs
   are provided here.

   IPsec channels where the peers were authenticated by methods other
   than public key cryptography, such as EAP [RFC3748] or pre-shared
   keys (PSK), or where IKEv2 was not used (e.g., manual keying), are
   out of scope for this document.  Channel bindings for such IPsec
   channels should be specified elsewhere, if at all (see

   The primary feature of IPsec end-point channel bindings as specified
   here is this: there is no reference to the actual contents of any key
   exchanges other than the public keys used therein.  Algorithm
   negotiations, nonces, session keys, and so on are of no consequence.
   And no additional message exchanges of any kind are needed in order
   to establish the end-point channel bindings for an IPsec channel.

1.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2.  IPsec Unique Channel Bindings

   The end-point channel bindings for IPsec channels established via
   connection latching [I-D.ietf-btns-connection-latching] between peers
   that use IKEv2 [RFC4306] and public keys (with or without PKIX
   certificates [RFC3280]) SHALL be:


   Where HASH() is a cryptographic hash function selected by the
   application requesting the end-point channel bindings.
   Implementations MUST support the use of SHA-256 [RFC4634].  ID1 and
   ID2 are the raw public keys of each peer.  If a peer uses a
   certificate, the value of the subjectPublicKey field (a BIT STRING)
   of the certificate's subjectPublicKeyInfo field is to be used
   verbatim.  If a peer uses a Raw RSA CERT payload, then the
   Certificate Data portion of that CERT payload will be used verbatim.
   XOR is used here to avoid having to determine an order in which end-
   point IDs should be used.

   The rationale for using hashes of public keys is: to greatly reduce
   the size of channel binding data that might need to be tracked in
   kernel-mode implementations (as we'd otherwise use the raw public key
   bit strings, which can be in excess of a kilobyte).

2.1.  API Requirements

   Because of the use of a hash function which must be selected by the
   application, implementations of IPsec connection latching and end-
   point channel bindings MUST provide a way, in the API for obtaining
   channel bindings, for the application to select the hash function to

   Since hash agility here depends on the application and its ability to
   negotiate hash functions for this purpose, implementations MUST
   provide an API for listing the supported hash functions.

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3.  IANA Considerations

   This document creates a type of channel binding, and so requires
   registration in the IANA channel binding registry (set out by

   The registration procedure will be followed when this document enters
   the RFC-Editor queue.  The registration will be as follows:

   o  Channel binding unique prefix (name): IPsec-end-point-IKEv2-

   o  Channel binding type: end-point

   o  Channel type: IPsec

   o  Published specification: <TBD>

   o  Channel binding is secret: no

   o  Description: see Section 2

   o  Intended usage: COMMON

   o  Contact: this document's author/editor

   o  Owner/Change controller: IETF

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4.  Security Considerations

   The security considerations of [RFC5056],
   [I-D.ietf-btns-connection-latching], and IPsec generally [RFC4301]
   apply.  The security of an application using channel binding to IPsec
   channels depends critically on the overall security of each of these
   components: IPsec [RFC4301], including the Internet Key Exchange
   (IKEv2) protocol [RFC4306], ESP/AH [RFC4303] [RFC4302], IPsec
   connection latching [I-D.ietf-btns-connection-latching], and the
   application's authentication and channel binding mechanism
   (potentially too many to reference here, but a common example is
   likely to be the Kerberos V mechanism [RFC4121] for the Generic
   Security Services API (GSS-API) [RFC2743].  A compromise of any one
   of those components may compromise the application to varying

   This document describes end-point channel bindings for some IPsec
   channels.  End-point channel bindings do not uniquely identify a
   connection in time, but a pair of peers.  This is sufficient to
   detect man-in-the-middle attacks via channel binding.  There are no
   additional security considerations, relating to the type of this
   channel binding, beyond those described in [RFC5056].

   Use of non-pre-shared Raw RSA public keys or certificates that cannot
   be validated to a given trust anchor is supported in the Better Than
   Nothing (BTNS) [I-D.ietf-btns-prob-and-applic] [I-D.ietf-btns-core]
   model.  When combined with connection latching and channel binding
   BTNS can provide all the security that an application requires but
   without having to deploy an IPsec authentication infrastructure
   (e.g., a PKI, manual pre-sharing of raw RSA public keys and/or self-
   signed certificates).

   The construction of IPsec end-point channel bindings described herein
   depends on the strength of the public key algorithms used by the
   IPsec peers to authenticate each other.  Because we use hashes of
   _public_ keys this construction does not require confidentiality
   protection of the channel bindings.

   We use a hash function in the construction of IPsec channel bindings.
   Correspondingly, we provide for hash agility, but we push the
   responsibility for hash agility to the application.  Applications
   cannot know what hash function their peers support without
   negotiating a hash function.  Supporting multiple hash functions
   requires computing the end-point channel bindings for each supported
   hash function, and it requires storing, in each IPsec channel, all
   the those end-point channel bindings.  Thus minimizing the number of
   supported hash functions is important.

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5.  References

5.1.  Normative References

              Williams, N., "IPsec Channels: Connection Latching",
              draft-ietf-btns-connection-latching-06 (work in progress),
              February 2008.

              Richardson, M. and B. Sommerfeld, "Requirements for an
              IPsec API", draft-ietf-btns-ipsec-apireq-00 (work in
              progress), April 2006.

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

   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              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.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC4634]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and HMAC-SHA)", RFC 4634, July 2006.

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, November 2007.

5.2.  Informative References

              Williams, N. and M. Richardson, "Better-Than-Nothing-
              Security: An Unauthenticated Mode of IPsec",
              draft-ietf-btns-core-06 (work in progress), January 2008.


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              Touch, J., Black, D., and Y. Wang, "Problem and
              Applicability Statement for Better Than Nothing Security
              (BTNS)", draft-ietf-btns-prob-and-applic-06 (work in
              progress), October 2007.

              Williams, N., "Unique Channel Bindings for IPsec Using
              IKEv2", draft-williams-ipsec-unique-channel-binding-00
              (work in progress), April 2008.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

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

   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism: Version 2", RFC 4121,
              July 2005.

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Author's Address

   Nicolas Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727

   Email: Nicolas.Williams@sun.com

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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
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