Internet DRAFT - draft-smyslov-ipsecme-ikev2-auth-announce
draft-smyslov-ipsecme-ikev2-auth-announce
Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS
Intended status: Standards Track August 31, 2021
Expires: March 4, 2022
Announcing Supported Authentication Methods in IKEv2
draft-smyslov-ipsecme-ikev2-auth-announce-04
Abstract
This specification defines a mechanism that allows the Internet Key
Exchange version 2 (IKEv2) implementations to indicate the list of
supported authentication methods to their peers while establishing
IKEv2 Security Association (SA). This mechanism improves
interoperability when IKEv2 partners are configured with multiple
different credentials to authenticate each other.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Exchanges . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. SUPPORTED_AUTH_METHODS Notify . . . . . . . . . . . . . . 4
3.2.1. 2-octet Announcement . . . . . . . . . . . . . . . . 5
3.2.2. 3-octet Announcement . . . . . . . . . . . . . . . . 6
3.2.3. Multi-octet Announcement . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Internet Key Exchange version 2 (IKEv2) protocol, defined in
[RFC7296], performs authenticated key exchange in IPsec. IKEv2,
unlike its predecessor IKEv1, defined in [RFC2409], doesn't include a
mechanism to negotiate an authentication method that the peers would
use to authenticate each other. It is assumed that each peer selects
whatever authentication method it thinks is appropriate, depending on
authentication credentials it has.
This approach generally works well when there is no ambiguity in
selecting authentication credentials. The problem may arise when
there are several credentials of different type configured on one
peer, while only some of them are supported on the other peer.
Another problem situation is when a single credential may be used to
produce different types of authentication tokens (e.g. signatures of
different formats). Emerging post-quantum signature algorithms may
bring additional challenges for implementations, especially if so
called hybrid schemes are used (e.g. see
[I-D.ounsworth-pq-composite-sigs]).
This specification defines an extension to the IKEv2 protocol that
allows peers to announce their supported authentication methods, thus
decreasing risks of SA establishment failure in situations when there
are several ways for the peers to authenticate themselves.
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2. Terminology and Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Protocol Details
The idea is that each party sends a list of authentication methods it
supports to its peer. In addition, the sending party may optionally
specify that some of the authentication methods are only to be used
with particular trust anchors. Upon receiving this information the
peer may take it into account while selecting an algorithm for its
authentication if several methods are available.
3.1. Exchanges
If the responder is willing to use this extension, it includes a new
notification SUPPORTED_AUTH_METHODS in a response message of the
IKE_SA_INIT exchange. This notification contains a list of
authentication methods supported by the responder.
Initiator Responder
----------- -----------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ,]
[N(SUPPORTED_AUTH_METHODS)]
Figure 1: IKE_SA_INIT Exchange
If the initiator doesn't support this extension, it will ignore the
received notification as an unknown status notify. Otherwise, it MAY
send the SUPPORTED_AUTH_METHODS notification in the IKE_AUTH request
message, with a list of authentication methods supported by the
initiator.
Initiator Responder
----------- -----------
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2, TSi, TSr,
[N(SUPPORTED_AUTH_METHODS)] } -->
<-- HDR, SK {IDr, [CERT,]
AUTH, SAr2, TSi, TSr }
Figure 2: IKE_AUTH Exchange
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Since the responder sends the SUPPORTED_AUTH_METHODS notification in
the IKE_SA_INIT exchange, it must take care that the size of the
response message wouldn't grow too much so that IP fragmentation
takes place. If the following conditions are met:
o the SUPPORTED_AUTH_METHODS notification to be included is so
large, that the responder suspects that IP fragmentation of the
resulting IKE_SA_INIT response message may happen;
o both peers support the IKE_INTERMEDIATE exchange, defined in
[I-D.ietf-ipsecme-ikev2-intermediate] (i.e. the responder has
received and is going to send the INTERMEDIATE_EXCHANGE_SUPPORTED
notification);
then the responder may choose not to send actual list of the
supported authentication methods in the IKE_SA_INIT exchange and
instead ask the initiator to start the IKE_INTERMEDIATE exchange for
the list to be sent in. In this case the responder includes
SUPPORTED_AUTH_METHODS notification containing no data in the
IKE_SA_INIT response.
If the initiator receives the empty SUPPORTED_AUTH_METHODS
notification in the IKE_SA_INIT exchange, it means that the responder
is going to send the list of the supported authentication methods in
the IKE_INTERMEDIATE exchange. If this exchange is to be initiated
anyway for some other reason, then the responder MUST use it to send
the SUPPORTED_AUTH_METHODS notification. Otherwise, the initiator
MAY start the IKE_INTERMEDIATE exchange just for this sole purpose by
sending an empty request message.
Initiator Responder
----------- -----------
HDR, SK {...} -->
<-- HDR, SK {...
[N(SUPPORTED_AUTH_METHODS)] }
Figure 3: IKE_INTERMEDIATE Exchange
Note, that sending the SUPPORTED_AUTH_METHODS notification and using
information obtained from it is optional for both the initiator and
the responder.
3.2. SUPPORTED_AUTH_METHODS Notify
The format of the SUPPORTED_AUTH_METHODS notification is shown below.
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ List of Supported Auth Methods Announcements ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SUPPORTED_AUTH_METHODS Notify
The Notify payload format is defined in Section 3.10 of [RFC7296].
When a Notify payload of type SUPPORTED_AUTH_METHODS is sent, the
Protocol ID field is set to 0, the SPI Size is set to 0, meaning
there is no SPI field, and the Notify Message Type is set to <TBA by
IANA>.
The Notification Data field contains the list of supported
authentication methods announcements. Each individual announcement
is a variable-size data blob, which format depends on the announced
authentication method. The blob always starts with an octet
containing the length of the blob followed by an octet containing the
authentication method. Authentication methods are represented as
values from the "IKEv2 Authentication Method" registry defined in
[IKEV2-IANA]. The meaning of the remaining octets of the blob, if
any, depends on the authentication method and is defined below.
Note, that for the currently defined authentication methods the
length octet fully defines both the format and the semantics of the
blob.
If more authentication methods are defined in future, the
corresponding documents must describe the semantics of the
announcements for these methods. Implementations MUST skip
announcements which semantics they don't understand.
3.2.1. 2-octet Announcement
If the announcement contains an authentication method that is not
concerned with public key cryptography, then the following format is
used.
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1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (=2) | Auth Method |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Supported Authentication Method
o Length - Length of the blob, must be 2 for this case.
o Auth Method - Announced authentication method.
This format is applicable for the authentication methods "Shared Key
Message Integrity Code" (2) and "NULL Authentication" (13). Note,
that authentication method "Generic Secure Password Authentication
Method" (12) would also fall in this category, however it is
negotiated separately (see [RFC6467] and for this reason there is no
point to announce it via this mechanism.
3.2.2. 3-octet Announcement
If the announcement contains an authentication method that is
concerned with public key cryptography, then the following format is
used. This format allows to link the announcement with a particular
trust anchor from the Certificate Request payload.
1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (=3) | Auth Method | Cert Link |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Supported Authentication Method
o Length - Length of the blob, must be 3 for this case.
o Auth Method - Announced authentication method.
o Cert Link - Link this announcement to a particular CA.
If the Cert Link field contains non-zero value N, it means that the
announced authentication method is intended to be used only with the
N-th trust anchor (CA certificate) from the Certificate Request
payload(s) sent by this peer. If it is zero, then this
authentication method may be used with any of CAs, that are not
linked to any other announcement. If multiple CERTREQ payloads were
sent, the CAs from all of them are treated as a single list for the
purpose of the linking. If no Certificate Request payload were
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receives, the content of this field MUST be ignored and treated as
zero.
This format is applicable for the authentication methods "RSA Digital
Signature" (1), "DSS Digital Signature" (3), "ECDSA with SHA-256 on
the P-256 curve" (9), "ECDSA with SHA-384 on the P-384 curve" (10)
and "ECDSA with SHA-512 on the P-512 curve" (11). Note however, that
these authentication methods are currently superseded by the "Digital
Signature" (14) authentication method, which has a different
announcement format, described below.
3.2.3. Multi-octet Announcement
The following format is currently used only with the "Digital
Signature" (14) authentication method.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (>3) | Auth Method | Cert Link | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
~ AlgorithmIdentifier ASN.1 object ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Supported Authentication Method
o Length - Length of the blob, must be greater than 3 for this case.
o Auth Method - Announced authentication method, currently may only
be 14 ("Digital Signature").
o Cert Link - Link this announcement to a particular CA; see
Section 3.2.2 for details.
o AlgorithmIdentifier ASN.1 object - DER-encoded ASN.1 object
AlgorithmIdentifier.
The "Digital Signature" authentication method, defined in [RFC7427],
supersedes previously defined signature authentication methods. In
this case the real authentication algorithm is identified via
AlgorithmIdentifier ASN.1 object. Appendix A in [RFC7427] contains
examples of Commonly Used ASN.1 Objects.
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4. Security Considerations
Security considerations for IKEv2 protocol are discussed in
[RFC7296]. It is assumed that this extension of the IKEv2 doesn't
add new vulnerabilities to the protocol.
5. IANA Considerations
This document defines a new Notify Message Types in the "Notify
Message Types - Status Types" registry:
<TBA> SUPPORTED_AUTH_METHODS
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in
the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
DOI 10.17487/RFC7427, January 2015,
<https://www.rfc-editor.org/info/rfc7427>.
[I-D.ietf-ipsecme-ikev2-intermediate]
Smyslov, V., "Intermediate Exchange in the IKEv2
Protocol", draft-ietf-ipsecme-ikev2-intermediate-07 (work
in progress), August 2021.
[IKEV2-IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters", <http://www.iana.org/assignments/ikev2-
parameters/ikev2-parameters.xhtml#ikev2-parameters-7>.
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6.2. Informative References
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<https://www.rfc-editor.org/info/rfc2409>.
[RFC6467] Kivinen, T., "Secure Password Framework for Internet Key
Exchange Version 2 (IKEv2)", RFC 6467,
DOI 10.17487/RFC6467, December 2011,
<https://www.rfc-editor.org/info/rfc6467>.
[I-D.ounsworth-pq-composite-sigs]
Ounsworth, M. and M. Pala, "Composite Signatures For Use
In Internet PKI", draft-ounsworth-pq-composite-sigs-05
(work in progress), July 2021.
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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