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+Network Working Group                                         Y. Sheffer
+Internet-Draft                                               Check Point
+Intended status: Informational                              July 6, 2008
+Expires: January 7, 2009
+
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+         Using EAP-GTC for Simple User Authentication in IKEv2
+                     draft-sheffer-ikev2-gtc-00.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 January 7, 2009.
+
+Abstract
+
+   Despite many years of effort, simple username-password authentication
+   is still prevalent.  In many cases a password is the only credential
+   available to the end user.  IKEv2 uses EAP as a sub-protocol for user
+   authentication.  This provides a well-specified and extensible
+   architecture.  To this day EAP does not provide a simple password-
+   based authentication method.  The only existing password
+   authentication methods either require the peer to know the password
+   in advance (EAP-MD5), or are needlessly complex when used within
+   IKEv2 (e.g.  PEAP).  This document codifies the common practice of
+   using EAP-GTC for this type of authentication, with the goal of
+   achieving maximum interoperability.  The various security issues are
+   extensively analyzed.
+
+
+
+Sheffer                  Expires January 7, 2009                [Page 1]
+
+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
+
+Table of Contents
+
+   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
+   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
+   3.  Alternatives to EAP-GTC in IKEv2  . . . . . . . . . . . . . . . 4
+     3.1.  Non-password credentials  . . . . . . . . . . . . . . . . . 4
+     3.2.  Using the IKE preshared secret  . . . . . . . . . . . . . . 4
+     3.3.  EAP-MD5 , EAP-MSCHAPv2 and mutual authentication
+           schemes . . . . . . . . . . . . . . . . . . . . . . . . . . 4
+   4.  Using EAP-GTC in IKE: Details . . . . . . . . . . . . . . . . . 5
+   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
+   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
+     6.1.  Key generation and MITM protection  . . . . . . . . . . . . 6
+     6.2.  Protection of credentials between the IKE gateway and
+           the AAA server  . . . . . . . . . . . . . . . . . . . . . . 6
+     6.3.  Server authentication . . . . . . . . . . . . . . . . . . . 6
+   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
+   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
+     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
+     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
+   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . . . 8
+     A.1.  -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
+   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8
+   Intellectual Property and Copyright Statements  . . . . . . . . . . 9
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+Sheffer                  Expires January 7, 2009                [Page 2]
+
+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
+
+1.  Introduction
+
+   "Oh dear!  It's possible that we have added EAP to IKE to support a
+   case that EAP can't support." -- C. Kaufman.
+
+   Despite many years of effort, simple username-password authentication
+   is still prevalent.  In many cases a password is the only credential
+   available to the end user.
+
+   IKEv2 [RFC4306] uses the Extensible Authentication Protocol (EAP) as
+   a sub-protocol for user authentication.  This provides a well-
+   specified and extensible architecture and enables useful capabilities
+   like SIM authentication.  Unfortunately, for a number of reasons EAP
+   still does not provide a simple password-based authentication method.
+   The only existing password authentication methods either require the
+   peer to know the password in advance (EAP-MD5), or are needlessly
+   complex when used within IKEv2 (e.g.  PEAP).
+
+   Technically, the IKE preshared secret authentication mode can be used
+   for password authentication.  In fact even the IKEv2 RFC winks at
+   this practice.  But this use jeopardizes the protocol's security and
+   should clearly be avoided (more details below).
+
+   EAP is used in IKEv2 at a stage when the remote access gateway has
+   already been authenticated.  At this point the user has a high enough
+   level of trust to send his or her password to the gateway.  Such an
+   exchange is enabled by the EAP Generic Token Card (GTC) method, which
+   is a simple text transport between the two EAP peers.  To quote
+   [RFC3748]:
+
+      The EAP GTC method is intended for use with the Token Cards
+      supporting challenge/response authentication and MUST NOT be used
+      to provide support for cleartext passwords in the absence of a
+      protected tunnel with server authentication.
+
+   IKEv2 does indeed provide "a protected tunnel with server
+   authentication".  The current document updates [RFC3748] by making an
+   exception and allowing the use of GTC to carry secret credentials, in
+   this specific situation.  Section 6 further elaborates on the
+   security properties of this solution.
+
+   Other protocols provide a similar protected tunnel, for example TLS-
+   EAP, described in [I-D.nir-tls-eap].  These protocols however are out
+   of scope for this document.
+
+
+
+
+
+
+
+Sheffer                  Expires January 7, 2009                [Page 3]
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+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
+
+2.  Terminology
+
+   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].
+
+
+3.  Alternatives to EAP-GTC in IKEv2
+
+   This section presents a few of the alternatives to EAP-GTC, and
+   explains why they are either insecure or impractical given today's
+   common identity management infrastructure.
+
+3.1.  Non-password credentials
+
+   Certificate-based authentication, especially when combined with
+   hardware protection (e.g. a hardware token), can be deployed in a
+   more secure manner than the form of password authentication which we
+   discuss.  However, due to a host of issues to do with cost,
+   inconvenience and reliability this solution has not gained wide
+   market acceptance over the last 10 years.
+
+3.2.  Using the IKE preshared secret
+
+   Sec. 2.15 of RFC 4306 points out that the generation of the IKE
+   preshared secret from a weak password is insecure.  Such use is
+   vulnerable to off line password guessing by an active attacker.  All
+   the attacker needs to do is respond correctly to the first IKE_INIT
+   message, and then record the third IKE message.  This is then
+   followed by a dictionary attack to obtain the password.
+
+3.3.  EAP-MD5 , EAP-MSCHAPv2 and mutual authentication schemes
+
+   Challenge-response schemes, like EAP-MD5 and EAP-MSCHAPv2, have a
+   clear security advantage over sending the plaintext password to the
+   gateway.  Password-based mutual authentication schemes like SRP have
+   a further advantage in that the gateway's authentication is much
+   stronger than when using certificates alone, since the AAA server
+   proves its knowledge of a per-client credential, and the gateway
+   proves that it has been authorized by the AAA server for that
+   particular client.
+
+   Unfortunately all of these methods also suffer from a major drawback:
+   the gateway must have a priori access to the plaintext password.
+   While many RADIUS servers may indeed have such access, other very
+   common deployments do not provide it.  One typical example is when
+   the gateway directly accesses an LDAP directory (or a Microsoft
+   Active Directory) to authenticate the user.  The usual way to do that
+
+
+
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+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
+
+   is by issuing an LDAP Bind operation into the directory, using the
+   just-received plaintext password.  Often in this case it is the IKE
+   gateway that terminates the EAP protocol, and it needs a way to
+   obtain the raw password.
+
+   An additional issue with mutual authentication schemes is their heavy
+   IP encumbrance, which has resulted in a scarcity of standards using
+   them and a low rate of market adoption.
+
+
+4.  Using EAP-GTC in IKE: Details
+
+   EAP-GTC is specified in [RFC3748], Sec. 5.6.  This section is non-
+   normative, and is merely an interpretation of this specification in
+   the context of IKEv2.
+
+   Simple authentication requires a non secret identity ("user name")
+   and a secret credential ("password").  Both of these are arbitrary
+   Unicode strings, although implementations may impose length
+   constraints.
+
+   In the case of EAP-GTC, the user name is conveyed in the IKE IDi
+   payload.  According to [RFC4718], Sec. 3.4, the user name can be
+   encoded in one of two ways: as a simple user name, in which case the
+   ID_KEY_ID identification type is used; or as a combination user name
+   plus realm, in which case the format is a NAI [RFC4282] and the
+   identification type is ID_RFC822_ADDR.  In either case, the user name
+   is a Unicode string encoded as UTF-8.  Using the EAP Identity payload
+   is redundant, and if it is used, it should be identical to the IDi
+   payload.
+
+   EAP-GTC consists of a simple 2-message exchange.  The contents of the
+   Type-Data field in the Request should not be interpreted in any way,
+   and should be displayed to the user.  This field contains a Unicode
+   string, encoded as UTF-8.
+
+   The password is sent in the EAP Response.  The Type-Data field of the
+   Response is also a Unicode string encoded as UTF-8.  Note that none
+   of the IDi payload, the EAP Request or the EAP Response is null-
+   terminated.
+
+   If either or both the user name and the password are non-ASCII, they
+   should be normalized by the IKE client before the IKE/EAP message is
+   constructed.  The normalization method is SASLprep, [RFC4013].
+
+
+
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+
+
+Sheffer                  Expires January 7, 2009                [Page 5]
+
+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
+
+5.  IANA Considerations
+
+   This document does not require any action by IANA.
+
+
+6.  Security Considerations
+
+6.1.  Key generation and MITM protection
+
+   Modern EAP methods generate a key shared between the two protocol
+   peers.  GTC does not (and cannot) generate such a key.  RFC 4306
+   mandates that:
+
+      EAP methods that do not establish a shared key SHOULD NOT be used,
+      as they are subject to a number of man-in-the-middle attacks
+      [EAPMITM] if these EAP methods are used in other protocols that do
+      not use a server-authenticated tunnel.
+
+   However GTC must never be used in such a situation, since the client
+   would be sending its credentials openly to an unauthenticated server.
+   When using GTC with IKEv2, the implementation (or local
+   administrators) MUST ensure that the same credentials are never used
+   in such a manner.
+
+6.2.  Protection of credentials between the IKE gateway and the AAA
+      server
+
+   In the proposed solution, the raw credentials are sent from the IKE
+   gateway to a AAA server, typically a RADIUS server.  These
+   credentials and the associated messaging MUST be strongly protected.
+   Some of the existing options include:
+   o  An IPsec tunnel between the gateway and the AAA server.
+   o  RADIUS over TCP with TLS, [I-D.winter-radsec].
+   o  RADIUS over UDP with DTLS, [I-D.dekok-radext-dtls] (expired).
+   The legacy RADIUS security mechanism (Sec. 5.2 of [RFC2865]) is
+   considered weak and SHOULD NOT be used when better alternatives are
+   available.
+
+6.3.  Server authentication
+
+   The client may only send its cleartext credentials after it has
+   positively authenticated the server.  This authentication is
+   specified, albeit rather vaguely, in [RFC4306] and is out of scope of
+   the current document.  Unauthenticated (BTNS) derivatives of IKE MUST
+   NOT be used with EAP-GTC.
+
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+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
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+7.  Acknowledgments
+
+   I would like to thank Yoav Nir and Charlie Kaufman for their helpful
+   comments.
+
+
+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.
+
+   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
+              Levkowetz, "Extensible Authentication Protocol (EAP)",
+              RFC 3748, June 2004.
+
+   [RFC4013]  Zeilenga, K., "SASLprep: Stringprep Profile for User Names
+              and Passwords", RFC 4013, February 2005.
+
+   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
+              RFC 4306, December 2005.
+
+8.2.  Informative References
+
+   [EAPMITM]  Asokan, N., Niemi, V., and K. Nyberg, "Man-in-the-Middle
+              in Tunneled Authentication Protocols", November 2002,
+              <http://eprint.iacr.org/2002/163>.
+
+   [I-D.dekok-radext-dtls]
+              DeKok, A., "DTLS as a Transport Layer for RADIUS",
+              draft-dekok-radext-dtls-00 (work in progress),
+              February 2007.
+
+   [I-D.nir-tls-eap]
+              Nir, Y., Tschofenig, H., and P. Gutmann, "TLS using EAP
+              Authentication", draft-nir-tls-eap-03 (work in progress),
+              April 2008.
+
+   [I-D.winter-radsec]
+              Winter, S., McCauley, M., and S. Venaas, "RadSec Version 2
+              - A Secure and Reliable Transport for the RADIUS
+              Protocol", draft-winter-radsec-01 (work in progress),
+              February 2008.
+
+   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
+              "Remote Authentication Dial In User Service (RADIUS)",
+              RFC 2865, June 2000.
+
+
+
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+Internet-Draft              EAP-GTC in IKEv2                   July 2008
+
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+   [RFC4282]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
+              Network Access Identifier", RFC 4282, December 2005.
+
+   [RFC4718]  Eronen, P. and P. Hoffman, "IKEv2 Clarifications and
+              Implementation Guidelines", RFC 4718, October 2006.
+
+
+Appendix A.  Change Log
+
+A.1.  -00
+
+   Initial version.
+
+
+Author's Address
+
+   Yaron Sheffer
+   Check Point Software Technologies Ltd.
+   5 Hasolelim St.
+   Tel Aviv  67897
+   Israel
+
+   Email: yaronf@checkpoint.com
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+Full Copyright Statement
+
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