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Versions: 00 01 02 03                                                   
Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Intended status: Standards Track                            July 1, 2014
Expires: January 2, 2015

            The NULL Authentication Method in IKEv2 Protocol


   This document introduces the NULL Authentication Method for the IKEv2
   Protocol.  This method provides a way to omit peer authentication in
   the IKEv2.  It may be used to preserve anonymity of or in the
   situations, where no trust relationship exists between the parties.

Status of this Memo

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

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   This Internet-Draft will expire on January 2, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Conventions Used in This Document . . . . . . . . . . . . . 3
   2.  Using the NULL Authentication Method  . . . . . . . . . . . . . 4
     2.1.  Authentication Payload  . . . . . . . . . . . . . . . . . . 4
     2.2.  Identity Payload  . . . . . . . . . . . . . . . . . . . . . 4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   The Internet Key Exchange Protocol version 2 (IKEv2), specified in
   [IKEv2], provides a way for two parties to perform authenticated key
   exchange.  Mutual authentication is mandatory in the IKEv2, so that
   each party must be authenticated by the other.  However the
   authentication methods, used by the peers, need not be the same.

   In some situations mutual authentication is undesirable, superfluous
   or impossible.  For example:

   o  User wants to get anonymous access to some server.  In this
      situation he/she should be able to authenticate the server, but to
      leave out his/her own authentication to preserve anonymity.  In
      this case one-way authentication is desirable.

   o  User wants to get some simple action from the remote device.
      Consider garage door opener: it must authenticate user to open the
      door, but it is not necessary for the user to authenticate the
      door opener.  In this case one-way authentication is sufficient.

   o  Two peers without any trust relationship want to get some level of
      security in their communications.  Without trust relationship they
      cannot prevent active Man-in-the-Middle attacks, but it is still
      possible to prevent passive eavesdropping with opportunistic
      encryption.  In this case they can use unauthenticated key

   To meet these needs the document introduces the NULL Authentication
   Method, which is a "dummy" method, that provides no authentication.
   This allows peer to explicitly indicate to the other side that it is
   unwilling or unable to certify its identity.

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.  Using the NULL Authentication Method

   In IKEv2 each peer independently selects the method to authenticate
   itself to the other side.  It means that any of the peers may choose
   to omit its authentication by using the NULL Authentication Method.
   If it is not acceptable for the other peer, it MUST return
   AUTHENTICATION_FAILED Notification.  Note, that when the Initiator
   uses EAP, the Responder MUST NOT use the NULL Authentication Method
   (in conformance with the section 2.16 of [IKEv2]).

   The NULL Authentication Method affects how the Authentication and the
   Identity payloads are formed in the IKE_AUTH Exchange.

2.1.  Authentication Payload

   Despite the fact that the NULL Authentication Method provides no
   authentication, the AUTH Payload must still be present in the
   IKE_AUTH Exchange messages and must be properly formed, as it
   cryptographically links the IKE_SA_INIT Exchange messages with the
   other messages sent over the IKE SA.

   With the NULL Authentication Method the content of the AUTH Payload
   MUST be computed using the syntax for pre-shared secret
   authentication, described in Section 2.15 of [IKEv2].  The values
   SK_pi and SK_pr MUST be used as shared secrets for the content of the
   AUTH Payloads generated by Initiator and Responder respectively.
   Note, that this is exactly how the content of the two last AUTH
   Payloads is calculated for non-key generating EAP Method (see Section
   2.16 of [IKEv2] for details).  The Auth Method field MUST be set to
   <TBA by IANA>.

2.2.  Identity Payload

   The NULL Authentication Method provides no authentication of the
   party using it.  For that reason the Identity Payload content cannot
   be verified by the peer and MUST be ignored by the IKE.  Since peer
   identity is meaningless in this case, Identification Data SHOULD be
   omitted from the ID Payload and ID Type SHOULD be set to 0.
   Implementations supporting the NULL Authentication Method MUST NOT
   fail if they receive such "empty" ID Payload.

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3.  Security Considerations

   IKEv2 protocol provides mutual authentication of the peers.  If one
   peer uses the NULL Authentication Method, then this peer cannot be
   authenticated by the other side, and it makes authentication in IKEv2
   to be one-way.  If both peers use the NULL Authentication method, key
   exchange becomes unauthenticated, that makes it subject to the Man-
   in-the-Middle attack.

   The identity of the peer using the NULL Authenticated Method cannot
   be verified by the other side and, therefore, MUST NOT be used
   neither for authorization purposes, nor for policy decisions.  All
   peers who use the NULL Authenticated Method should be considered by
   the other party as "guests" and get the least possible privileges.
   If the peer uses the NULL Authenticated Method, then the content of
   its Traffic Selector Payloads must be treated with care.  In
   particular, implementations are advised not to trust blindly that the
   public IP addresses the peer put into TS Payload are really belong to
   it.  It is RECOMMENDED for security gateways to always assign
   internal IP addresses to unauthenticated clients as described in
   Section 2.19 of [IKEv2].

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4.  Acknowledgments

   The author would like to thank Paul Wouters, Yaron Sheffer and Tero
   Kivinen for their reviews and valuable comments.

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5.  IANA Considerations

   This document defines new value in the "IKEv2 Authentication Method"

     <TBA>       NULL Authentication Method

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6.  Normative References

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

   [IKEv2]    Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", draft-kivinen-ipsecme-ikev2-rfc5996bis-04 (work
              in progress), June 2014.

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Author's Address

   Valery Smyslov
   PO Box 81
   Moscow (Zelenograd)  124460
   Russian Federation

   Phone: +7 495 276 0211
   Email: svan@elvis.ru

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