wdiff draft-ietf-ipsecme-ikev2-null-auth-02.txt draft-ietf-ipsecme-ikev2-null-auth-03.txt

Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS
Intended status: Standards Track P. Wouters
Expires: July 17, August 1, 2015 Red Hat
January 13, 28, 2015

The NULL Authentication Method in IKEv2 Protocol
draft-ietf-ipsecme-ikev2-null-auth-02
draft-ietf-ipsecme-ikev2-null-auth-03

Abstract

This document specifies the NULL Authentication Method method and the
ID_NULL Identification Payload ID Type for the IKEv2 Protocol. This
allows two IKE peers to establish single-side authenticated or mutual
un-authenticated
unauthenticated IKE sessions for those use cases where a peer is
unwilling or unable to authenticate or identify itself. This ensures
IKEv2 can be used for Opportunistic Security (also known as Opportunsitic
Opportunistic Encryption) to defend against Pervasive Monitoring
attacks without the need to sacrifice anonimity. anonymity.

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 5
2.1. Authentication Payload . . . . . . . . . . . . . . . . . . 4 5
2.2. Identity Identification Payload . . . . . . . . . . . . . . . . . . . . . 4 5
2.3. INITIAL_CONTACT Notification . . . . . . . . . . . . . . . 5 6
2.4. Interaction with Peer Authorization Database (PAD) . . . . 6
2.5. Traffic Selectors . . . . . . . . . . . . . . . . . . . . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8
3.1. Audit trail and peer identification . . . . . . . . . . . 6 8
3.2. Resource management and robustness . . . . . . . . . . . . 6 8
3.3. IKE configuration selection . . . . . . . . . . . . . . . 7 9
3.4. Networking topology changes . . . . . . . . . . . . . . . 7
3.5. Priviledged IKE operations . . . . . . . . . . . . . . . . 8 9
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 12
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11 12
6.2. Informative References . . . . . . . . . . . . . . . . . . 11 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 13

1. Introduction

The Internet Key Exchange Protocol version 2 (IKEv2), specified in
[RFC7296], provides a way for two parties to perform an authenticated
key exchange. While the authentication methods used by the peers can
be different, there is no method for one or both parties to remain
unauthenticated and anonymous. This document extends the
authentication methods to support unauthenticated key exchanges. and anonymous IKE
sessions.

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

o A user wants to establish an anonymous secure connection to a
server. In this situation the user should be able to authenticate
the server without presenting or authenticating to the server with
their own identity. This case uses a single-sided authentication
of the responder.

o A sensor that periodically wakes up from a suspended state wants
to send a measurement (e.g. temperature) to a collecting server.
The sensor must be authenticated by the server to ensure
authenticity of the measurment, measurement, but the sensor does not need to
authenticate the server. This case uses a single-sided
authentication of the initiator.

o Two peers without any trust relationship wish to defend against
widespread pervasive monitoring attacks as described in [RFC7258].
Without a trust relationship, the peers cannot authenticate each
other. Opportunistic Security [RFC7435] states that un-
authenticated
unauthenticated encrypted communication is prefered preferred over
cleartext communication. The peers want to use IKE to setup an un-
authenticated
unauthenticated encrypted connection, that gives them protection
against pervasive monitoring attacks. An attacker that is able
and willing to send packets can still launch an Man-in-the-Middle
attack to obtain access to the decrypted communication. This case
uses a fully anonymous un-authenticated unauthenticated key exchange.

To meet these needs this document introduces the NULL authentication Authentication
method, and the ID_NULL identity ID type. This allows an IKE peer to
explicitly indicate 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, each peer independently selects the method to authenticate
itself to the other side. A peer may choose to refrain from
authentication by using the NULL Authentication Method. method. If a peer
that requires authentiation authentication receives an AUTH payload containing the
NULL Authentication Method method type, it MUST return an
AUTHENTICATION_FAILED notification. If an initiator uses EAP, the
responder MUST NOT use the NULL Authentication Method (in conformance
with the section 2.16 of [RFC7296]).

The

NULL Authentication Method affects how the Authentication and the
Identity
Identification payloads are formed in the IKE_AUTH exchange.

2.1. Authentication Payload

The

NULL Authentication Method still requires a properly formed AUTH payload to
be present in the IKE_AUTH exchange messages, as the AUTH payload
cryptographically links the IKE_SA_INIT exchange messages with the
other messages sent over this IKE SA.

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

The KEv2 IKEv2 Authentication Method value for the NULL Authentication
Method is 13.

2.2. Identity Identification Payload

When a remote peer is not authenticated, any ID presented in the
Identification Data field of the Identification Payload ID payload cannot be
validated and MUST be ignored. A new Identification Payload ID Type
is introduced to validated. To
avoid the need of sending a bogus ID Type with placeholder data. Furthermore, sending a traditional ID field might
unwittingly compromise the anonimity of the peer.

This data, this
specification defines a new ID Type of ID_NULL, which SHOULD
only be used with the NULL Authentication Method. Type, ID_NULL. The Identification
Data field of the Identification Payload ID payload for this ID Type MUST be empty.

The IKEv2 Identification Payload ID Type for ID_NULL is 13.

2.3. INITIAL_CONTACT Notification

The identity of the peer which uses the

If NULL Authentication Method
cannot is in use and an anonymity is a concern then
ID_NULL SHOULD be used in Identification payload. In some cases
there may be good reasons to distinguish between IKE SAs created by different
peers. For that reason the INITIAL_CONTACT notifications MUST use non-null identities (and ID Types
other than ID_NULL) with NULL Authentication. The identities may be
ignored
used for IKE SAs using logging, troubleshooting or in scenarios when authentication
takes place out of band after the NULL Authentication Method.

When a new IKE SA is established using the created (like in
[AUTOVPN]). In any case, when NULL Authentication
Method, implementations MAY perform a Liveness is employed, the
content of Identification payload MUST NOT be used for any trust and
policy checking in IKE_AUTH exchange.

ID_NULL is primarily intended to be used with the NULL
Authentication, but it MAY also be used in other situations, when the
content of Identification payload does not matter. For example,
ID_NULL can be used when authentication is performed via raw public
keys and the identities are these keys themselves. Another example
is EAP authentication when the client identity in ID payload is not
used.

The IKEv2 Identification Payload ID Type for ID_NULL is 13.

2.3. INITIAL_CONTACT Notification

The identity of a peer using NULL Authentication cannot be used to
distinguish from IKE SAs created by other peers using the NULL
Authentication method. For that reason the INITIAL_CONTACT
notifications MUST be ignored for IKE SAs using NULL Authentication.

The standard IKE Liveness Check procedure, decribed in Section 2.4 of
[RFC7296], can be used to detect stale IKE SAs created by peers using
NULL Authentication. Inactive unauthenticated IKE SAs should be
checked periodically. Additionally, the event of creating a new
unauthenticated IKE SA can be used to trigger an out-of-order check
on existing unauthenticated IKE SAs, possibly limited to identical or
close-by IP addresses or to identical identities of the just created
IKE SA.

Implementations should weight the resource consumption of sending
Liveness Checks against the memory usage of possible orphaned IKE
SAs. Implementations may choose to handle situations with thousands
of unauthenticated IKE SAs differently from situations with very few
such SAs.

2.4. Interaction with Peer Authorization Database (PAD)

Section 4.4.3 of [RFC4301] defines the Peer Authorization Database
(PAD), which provides the link between Security Policy Database (SPD)
and the IKEv2. The PAD contains an ordered list of records, with
peers' identities along with corresponding authentication data and
Child SA authorization data. When the IKE SA is being established
the PAD is consulted to determine how the peer should be
authenticated and what Child SAs it is authorized to create.

When using NULL Authentication, the peer identity is not
authenticated and cannot be used. If ID_NULL is used with NULL
Authentication, there is no ID at all. The processing of PAD
described in Section 4.4.3.4 of [RFC4301] must be updated.

If NULL Authentication is supported and allowed, then a special entry
MUST be included in the PAD. This entry MUST contain no
authentication data. It MAY contain a set of constraints for
creating Child SAs as described in Section 4.4.3 of [RFC4301]. When
a peer uses NULL Authentication, regular matching rules for the PAD
MUST be ignored and this special entry MUST be selected regardless of
the peer identity. Likewise, if a peer uses any other authentication
method, then this special entry MUST NOT be selected regardless of
the peer identity and the regular search of the PAD described in
Section 4.4.3.4 of [RFC4301] MUST be performed.

Implementations SHOULD allow to be configured so, that when a peer
requests NULL Authentication, then regular PAD entries are searched
before selecting the special entry, to ensure that there is no entry,
containing peer's IP address. In this case implementations MUST
reject the IKE_AUTH exchange by sending an AUTHENTICATION_FAILED
notification if such an entry is found.

2.5. Traffic Selectors

Traffic Selectors and narrowing allow two IKE peers to mutually agree
on a traffic range for an IPsec SA. An unauthenticated peer must not
be allowed to use this mechanism to steal traffic that 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 address that are different from the
source IP of their IKE packets. A rogue IKE peer could use malicious
Traffic Selectors to 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 method to achieve this is to always assign internal IP addresses
to unauthenticated IKE
SAs that were established using the NULL Authentication Method. To
mitigate the potential impact of sending Liveness Check messages on a
large number clients, as described in Section 2.19 of
[RFC7296]. Implementations may also use other techniques, such as
internal NAT and connection tracking.

Implementations MAY force unauthenticated IKE SAs, implementations are advised peers to single host-
to-host IPsec SAs. When using IPv6 it is not always possible, so in
this case implementations MUST be able to blindly
perform Liveness Check on every such SA, but assign full /64 address
block to take into
considerations additional information, that may indicate that the
particular SA peer as described in [RFC5739], even if it is alive. This information may include the recent
receipt of cryptographically protected message on the IKE SA or any
of its Child SAs, or a successfull Liveness Check that was performed
recently. not
authenticated.

3. Security Considerations

If authenticated IKE sessions are possible between the peers, then
unauthenticated IKE SHOULD NOT be used, unless implementations make
sure to keep authenticated and unauthenticated IKE sessions separate,
and has policy rules to specify when to use which IKE session. See
[RFC7435] for details.

If both peers use the NULL Authentication Method, Authentication, the entire key exchange
becomes unauthenticated. This makes the IKE session vulnerable to
active Man-in-the-Middle Attacks. Un-authenticated IKE
sessions MUST only attempted when authenticated IKE sessions are not
possible for the remote host and the only alternative would be to
send plaintext. See [RFC7435] for details.

Implementations SHOULD use the ID_NULL Identity Type with the NULL
Authenticated Method. If an un-authenticated remote IKE peer
presents an Identity Type different from ID_NULL, the Identification
Payload data MUST NOT be used for anything except logging.

Using an ID Type other than ID_NULL with the NULL Authentication
Method compromises may compromise the client's anonimity. This should be avoided
for regular operation but could be temporarilly enabled, for example
to aid with troubleshooting diagnostics. Sending an unverifiable
identification for any other purpose is strongly discouraged as it
leads to a false sense anonimity in case of security, an active
MITM attack.

IKE implementations without the NULL Authentication Method have always performed
mutual authentication and were not designed for use with un-authenticated
unauthenticated IKE peers. Implementations might have made
assumptions that are 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 unauthenticated
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 the system or network.
Implementations
Implementers that add the implement NULL 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 resource
consumption of half-open IKE SAs. Furthermore, [DDOS-PROTECTION]
offers additional counter-meassures counter-measures in an attempt to distinguish
attacking IKE packets from legitimate IKE peers.

These defense mechanisms do not take into account IKE systems that
allow un-authenticated unauthenticated IKE peers. An attacker using the NULL
Authentication Method is a fully legitimate IKE peer that is only
distinguished from authenticated IKE peers by the Authenticaion
Method having used NULL
Authentication.

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 unauthenticated IKE
peers, these implementation omissions and errors will be found and
abused by attackers. For example, an un-authenticated unauthenticated IKE peer could
send an abusive amount of Liveness probes or Delete requests.

3.3. IKE configuration selection

Combining authenticated and un-authenticated unauthenticated IKE peers on a single
host can be dangerous, assuming the authenticated IKE peer gains more
or different access from non-authenticated peers (otherwise, why not
only allow un-authentcated unauthenticated peers). An un-authenticated unauthenticated IKE peer MUST
NOT be able to reach resources only meant for authenticated IKE peers
and MUST NOT be able to replace the IPsec Child 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 IKE session, it MUST reject the
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 circumvent 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 unauthenticated IKE MUST pass all decrypted traffic
through the same packet filters and security mechanisms as plaintext
traffic.

Traffic 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 allowed to use this mechanism to steal traffic that 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 address that are different
from the source IP of their IKE packets. A rogue IKE peer could use
malicious Traffic Selectors to 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 to always assign internal IP
addresses to un-authenticated IKE clients, as described in Section
2.19 of [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 authors would like to thank Yaron Sheffer and Tero Kivinen for
their reviews and valuable comments.

5. IANA Considerations

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

13 NULL Authentication Method

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

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.

[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.

[RFC5739] Eronen, P., Laganier, J., and C. Madson, "IPv6
Configuration in Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 5739, February 2010.

[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", 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.

[AUTOVPN] Sheffer, Y. and Y. Nir, "The AutoVPN Architecture", Work
in Progress, draft-sheffer-autovpn-00, February 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), October 2014.

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