wdiff draft-ietf-ipsecme-ikev2-null-auth-01.txt draft-ietf-ipsecme-ikev2-null-auth-02.txt

Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS
Intended status: Standards Track October 22, 2014 P. Wouters
Expires: April 25, July 17, 2015 Red Hat
January 13, 2015

The NULL Authentication Method in IKEv2 Protocol
draft-ietf-ipsecme-ikev2-null-auth-01
draft-ietf-ipsecme-ikev2-null-auth-02

Abstract

This document introduces specifies the NULL authentication method Authentication Method and the
ID_NULL Identification Payload ID Type for the IKEv2 Protocol. This method provides a way
allows two IKE peers to omit establish single-side authenticated or mutual
un-authenticated IKE sessions for those use cases where a peer authentication in
the IKEv2. It may is
unwilling or unable to authenticate itself. This ensures IKEv2 can
be used for Opportunistic Security (also known as Opportunsitic
Encryption) to preserve anonymity of or in the
situations, where no trust relationship exists between defend against Pervasive Monitoring attacks without
the parties. need to sacrifice anonimity.

Status of this Memo

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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
2.3. INITIAL_CONTACT Notification . . . . . . . . . . . . . . . 4 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
3.1. Audit trail and peer identification . . . . . . . . . . . 6
3.2. Resource management and robustness . . . . . . . . . . . . 6
3.3. IKE configuration selection . . . . . . . . . . . . . . . 7
3.4. Networking topology changes . . . . . . . . . . . . . . . 7
3.5. Priviledged IKE operations . . . . . . . . . . . . . . . . 8
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . 9
Author's Address . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . 10 . . . . . . . . . . . . . . . 12

1. Introduction

The Internet Key Exchange Protocol version 2 (IKEv2), specified in
[IKEv2],
[RFC7296], provides a way for two parties to perform an authenticated
key exchange. Mutual authentication is mandatory in the IKEv2, so that
each party must be authenticated by the other. However While the authentication methods, methods used by the peers, need not peers can
be different, there is no method for one or both parties to remain
unauthenticated and anonymous. This document extends the same.
authentication methods to support unauthenticated key exchanges.

In some situations mutual authentication is undesirable, superfluous
or impossible. For example: The following three examples illustratate these un-
authenticated use cases:

o User A user wants to get establish an anonymous access secure connection to some a
server. In this situation he/she the user should be able to authenticate
the server, but server without presenting or authenticating to
leave out his/her the server with
their own authentication to preserve anonymity. In
this identity. This case one-way uses a single-sided authentication
of the responder is desirable. responder.

o Sensor, A sensor that sleeps most of the time, but periodically wakes up,
makes some measurment up from a suspended state wants
to send a measurement (e.g. temperature) and sends the results to
some a collecting server.
The sensor must be authenticated by the server to ensure
authenticity of the measurment, but the server need sensor does not be
authenticated by need to
authenticate the sensor. In this server. This case one-way uses a single-sided
authentication of the initiator is sufficient. initiator.

o Two peers without any trust relationship want wish to get some level of
security defend against
widespread pervasive monitoring attacks as described in their communications. [RFC7258].
Without a trust relationship they relationship, the peers cannot prevent active Man-in-the-Middle attacks, but it authenticate each
other. Opportunistic Security [RFC7435] states that un-
authenticated encrypted communication is prefered over cleartext
communication. The peers want to use IKE to setup an un-
authenticated encrypted connection, that gives them protection
against pervasive monitoring attacks. An attacker that is able
and willing to send packets can still
possible launch an Man-in-the-Middle
attack to prevent passive eavesdropping with opportunistic
encryption. In this obtain access to the decrypted communication. This case they can use unauthenticated
uses a fully anonymous un-authenticated key exchange.

To meet these needs the this document introduces the NULL authentication
method, which is a "dummy" method, that provides no authentication. and the ID_NULL identity type. This allows an IKE 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

2. Using the NULL Authentication Method

In IKEv2 IKEv2, each peer independently selects the method to authenticate
itself to the other side. It means that any of the peers A peer may choose to omit its refrain from
authentication by using the NULL authentication method. Authentication Method. If it is not acceptable for a peer
that requires authentiation receives an AUTH payload containing the other peer,
NULL Authentication Method type, it MUST return an
AUTHENTICATION_FAILED notification. Note, that when the If an initiator uses EAP, the
responder MUST NOT use the NULL authentication method Authentication Method (in conformance
with the section 2.16 of [IKEv2]). [RFC7296]).

The NULL authentication method 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

The NULL authentication method provides no
authentication, the Authentication Method still requires a properly formed AUTH
payload must still to be present in the IKE_AUTH exchange messages and must be properly formed, messages, as it the AUTH
payload cryptographically links the IKE_SA_INIT exchange messages
with the other messages sent over this IKE SA.

With

When using the NULL authentication method Authentication Method, the content of the AUTH
payload
MUST be is computed using the syntax for of pre-shared secret
authentication, described in Section 2.15 of [IKEv2]. [RFC7296]. The values
SK_pi and SK_pr MUST be are used as shared secrets for the content of the
AUTH payloads generated by the initiator and the responder
respectively. Note, Note that this is exactly identical to how the content of the
two last AUTH payloads is calculated generated for non-key generating the non-key-generating EAP method
methods (see Section 2.16 of [IKEv2] [RFC7296] for details).

The KEv2 Authentication Method value for the the NULL authentication method Authentication
Method is <TBA by IANA>. 13.

2.2. Identity Payload

The NULL authentication method provides no authentication of

When a remote peer is not authenticated, any ID presented in the
party using it. For that reason
Identification Data field of the Identity payload content Identification Payload cannot be verified by the peer
validated and MUST be ignored by the IKE.

This specification defines ignored. A new Identification Payload ID Type - ID_NULL, which
is intended introduced to be used avoid the need of sending a bogus ID Type with
placeholder data. Furthermore, sending a traditional ID field might
unwittingly compromise the NULL authentication method to explicitely
indicate anonymity anonimity of the peer.

This specification defines a new ID Type MUST NOT of ID_NULL, which SHOULD
only be used with
authentication methods, that provide real authentication. the NULL Authentication Method. The Identification
Data in Identity payload for field of the ID_NULL type Identification Payload MUST be
absent and the empty.

The IKEv2 Identification Payload ID Type for ID_NULL is set to <TBA by IANA>. 13.

2.3. INITIAL_CONTACT Notification

The identity of the peer which uses the NULL authentication method Authentication Method
cannot be used to distinguish betweed between IKE SAs created by different
peers, because the peers may use the same identity (for example all
endpoints which use identity of type ID_NULL).
peers. For that reason the INITIAL_CONTACT notification notifications MUST be
ignored if it is present by the
party for IKE SAs using the NULL authentication method. To find out stale Authentication Method.

When a new IKE
SAs in this situation, SA is established using the NULL Authentication
Method, implementations should MAY perform a Liveness Check on all other IKE
SAs with that were established using the same peer idenity as NULL Authentication Method. To
mitigate the newly created IKE
SA.

3. Security Considerations

IKEv2 protocol provides mutual authentication potential impact of sending Liveness Check messages on a
large number of IKE SAs, implementations are advised not to blindly
perform Liveness Check on every such SA, but to take into
considerations additional information, that may indicate that the peers. If one
peer uses
particular SA is alive. This information may include the NULL authentication method, then this peer cannot be
authenticated by recent
receipt of cryptographically protected message on the other side, and it makes authentication in IKEv2
to be one-way. IKE SA or any
of its Child SAs, or a successfull Liveness Check that was performed
recently.

3. Security Considerations

If both peers use the NULL Authentication method, Method, the entire key
exchange becomes unauthenticated, that unauthenticated. This makes it susceptible the IKE session
vulnerable to active
attacks. For that reason completely unauthenticated Man-in-the-Middle Attacks. Un-authenticated IKE SA must be
used
sessions MUST only if attempted when authenticated IKE sessions are not
possible for the remote host and the only alternative is would be to
send plaintext.

The identity of the peer using See [RFC7435] for details.

Implementations SHOULD use the ID_NULL Identity Type with the NULL authenticated method
cannot be verified by
Authenticated Method. If an un-authenticated remote IKE peer
presents an Identity Type different from ID_NULL, the other side and, therefore, Identification
Payload data MUST NOT be used
neither for authorization purposes, nor for policy decisions. All
peers who use anything except logging.

Using an ID Type other than ID_NULL with the NULL Authenticated Authentication
Method compromises the client's anonimity. This should be considered by
the avoided
for regular operation but could be temporarilly enabled, for example
to aid with troubleshooting diagnostics. Sending an unverifiable
identification for any other party purpose is strongly discouraged as "guests" and get it
leads to a false sense of security,

IKE implementations without the least possible privileges. NULL Authentication Method have
always performed mutual authentication and were not designed for use
with un-authenticated IKE peers. Implementations might have made
assumptions that are advised no longer valid. Furthermore, the host itself
might have made trust assumptions or may not be aware of the network
topology changes that resulted from IPsec SAs from un-authenticated
IKE peers.

3.1. Audit trail and peer identification

An established IKE session is no longer guaranteed to provide a
verifiable (authenticated) entity known to use the ID_NULL Identity Type with system or network.
Implementations that add the NULL authenticated method.

If endpoint receives a request Authentication Method should audit
their implementation for any assumptions that depend on IKE peers
being "friendly", "trusted" or "identifiable".

3.2. Resource management and robustness

Section 2.6 of [RFC7296] provides guidance for mitigation of "Denial
of Service" attacks by issuing COOKIES in response to create resource
consumption of half-open IKE SAs. Furthermore, [DDOS-PROTECTION]
offers additional counter-meassures in an unauthenticated attempt to distinguish
attacking IKE SA packets from legitimate IKE peers.

These defense mechanisms do not take into account IKE systems that
allow un-authenticated IKE peers. An attacker using the IP address, which NULL
Authentication Method is configured on a fully legitimate IKE peer that is only
distinguished from authenticated IKE peers by the endpoint Authenticaion
Method

While implementations should have been written to account for abusive
authenticated clients, any omission or error in handling abusive
clients may have gone unnoticed because abusive clients has been a
rare or non-existent problem. When enabling un-authenticated IKE
peers, these implementation omissions and errors will be
authenticated, the request SHOULD found and
abused by attackers. For example, an un-authenticated IKE peer could
send an abusive amount of Liveness probes or Delete requests.

3.3. IKE configuration selection

Combining authenticated and un-authenticated IKE peers on a single
host can be rejected.

If dangerous, assuming the authenticated IKE peer uses gains more
or different access from non-authenticated peers (otherwise, why not
only allow un-authentcated peers). An un-authenticated IKE peer MUST
NOT be able to reach resources only meant for authenticated IKE peers
and MUST NOT be able to replace the IPsec SAs of an authenticated IKE
peer.

If an IKE peer receives an IKE_AUTH exchange requesting a NULL
Authentication Method from an IP address that matches a configured
connection for an authenticated method, then IKE session, it MUST reject the content of
its
IKE_AUTH exchange by sending an AUTHENTICATION_FAILED notification.

3.4. Networking topology changes

When a host relies on packet filters or firewall software to protect
itself, establishing an IKE SA and installing an IPsec SA might
accidentally circument these packet filters and firewall
restrictions, as the encrypted ESP (protocol 50) or ESPinUDP (UDP
port 4500) packets do not match the packet filters defined. IKE
peers supporting un-authenticated IKE MUST pass all decrypted traffic
through the same packet filters and security mechanisms as plaintext
traffic.

Traffic Selector payloads must Selectors and narrowing allow two IKE peers to mutually agree
on a traffic range for an IPsec SA. An un-authenticated peer MUST
NOT be treated with care. In
particular, implementations are advised not allowed to trust blindly use this mechanism to steal traffic that the
public an IKE
peer intended to be for another host. This is especially problematic
when supporting anonymous IKE peers behind NAT, as such IKE peers
build an IPsec SA using their pre-NAT IP addresses address that are different
from the source IP of their IKE packets. A rogue IKE peer put into TS payload are really belong could use
malicious Traffic Selectors to
it. It obtain access to traffic that the host
never intended to hand out. Implementations SHOULD restrict and
isolate all anonymous IKE peers from each other and itself and only
allow it access to itself and possibly its intended network ranges.

One of the ways to achive that is RECOMMENDED for security gateways to always assign internal IP
addresses to unauthenticated clients un-authenticated IKE clients, as described in Section
2.19 of [IKEv2]. [RFC7296]. Implementations may also use other techniques,
such as internal NAT and connection tracking. Implementations MAY
force un-authenticated IKE peers to single host-to-host IPsec SAs.

3.5. Priviledged IKE operations

Some IKE features are not appropriate for un-authenticated IKE peers
and should be restricted or forbidden.

4. Acknowledgments

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

5. IANA Considerations

This document defines a new value entry in the "IKEv2 Authentication
Method" registry:

<TBA>

13 NULL Authentication Method

This document also defines a new value entry in the "IKEv2 Identification
Payload ID Types" registry:

<TBA>

13 ID_NULL

6. References

6.1. Normative References

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

[IKEv2]

[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", draft-kivinen-ipsecme-ikev2-rfc5996bis-04 STD 79, RFC 7296, October 2014.

6.2. Informative References

[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, May 2014.

[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, December 2014.

[DDOS-PROTECTION]
Nir, Y., "Protecting Internet Key Exchange (IKE)
Implementations from Distributed Denial of Service
Attacks", draft-ietf-ipsecme-ddos-protection-00 (work in
progress), June October 2014.

Author's Address

Authors' Addresses

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

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

Paul Wouters
Red Hat

Email: pwouters@redhat.com