Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS
Intended status: Informational December 24, 2013
Expires: June 27, 2014
The NULL Authentication Method in IKEv2 Protocol
draft-smyslov-ipsecme-ikev2-null-auth-00
Abstract
This document defines the NULL Authentication Method for IKEv2
Protocol. This method provides a way to omit peer authentication in
IKEv2 and to explicitely indicate it in the protocol run. This
method may be used to preserve anonymity or in situations, where no
trust relationship exists between the parties.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . . 3
2. Using NULL Authentication Method . . . . . . . . . . . . . . . 4
2.1. Authentication Payload . . . . . . . . . . . . . . . . . . 4
2.2. Identity Payload . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The Internet Key Exchange Protocol version 2 (IKEv2), specified in
[RFC5996], 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, but
authentication methods, used by the peers, need not be the same.
In some situations mutual authentication is undesirable or
impossible. For example:
o User wants to get anonymous access to some resource. In this
situation he/she should be able to authenticate server, but to
leave out his/her own authentication to prevent anonymity. In
this case one-way authentication is desirable.
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 have to perform unauthenticated key
exchange.
To meet this needs the document introduces NULL Authentication
Method, which is effectively a "dummy" method, that provides no
authentication. This allows peer to explicitely indicate to the
other side that he is unwilling or unable to certify his identity.
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].
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2. Using NULL Authentication Method
NULL Authentication Method affects how Authentication and Identity
Payloads are formed in IKE_AUTH Exchange.
2.1. Authentication Payload
Even when peer uses NULL Authentication, the AUTH Payload must still
be present in IKE_AUTH Exchange and must be properly formed, as it
cryptographically links IKE_SA_INIT Messages with the other Messages
sent over IKE SA.
With NULL Authentication Method the content of AUTH Payload MUST be
computed using the syntax for pre-shared secret authentication,
described in Section 2.15 of [RFC5996]. The values SK_pi and SK_pr
MUST be used as shared secrets for AUTH Payloads generated by
Initiator and Responder respectively. Note, that this is exactly how
content of the two last AUTH Payloads is calculated in case of using
non-key generating EAP Method (see Section 2.16 of [RFC5996] for
details). The field Auth Method MUST be set to <to be assigned by
IANA>.
2.2. Identity Payload
NULL Authentication Method provides no authentication of the party
using it. For that reason Identity Payload content cannot be
verified by the other party and SHOULD be ignored. It MAY be used
for the purpose of audit, but it MUST NOT be used for any
authorization decisions. As peer identity is meaningless in this
case, Identification Data MAY be omited from ID Payload, in which
case ID Type MAY be set to any value. Implementations supporting
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 NULL Authentication Method, then this peer cannot be
authenticated by the other side, and it makes authentication in IKEv2
to become one-way. If both peers use NULL Authentication method, key
exchange becomes unauthenticated, that makes it subject to the Man-
in-the-Middle attack.
The identity of the peer using 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 NULL Authenticated Method should be considered by the other party
as "guests" and get the least possible privileges.
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4. IANA Considerations
This document defines new value in the "IKEv2 Authentication Method"
registry:
<TBA> NULL Authentication Method
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5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
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Author's Address
Valery Smyslov
ELVIS-PLUS
PO Box 81
Moscow (Zelenograd) 124460
RU
Phone: +7 495 276 0211
Email: svan@elvis.ru
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