Network Working Group P. Hoffman

Network Working Group P. Hoffman
Request for Comments: 4308 VPN Consortium
Category: Standards Track December 2005

Cryptographic Suites for IPsec

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2005).

Abstract

The IPsec, Internet Key Exchange (IKE), and IKEv2 protocols rely on
security algorithms to provide privacy and authentication between the
initiator and responder. There are many such algorithms available,
and two IPsec systems cannot interoperate unless they are using the
same algorithms. This document specifies optional suites of
algorithms and attributes that can be used to simplify the
administration of IPsec when used in manual keying mode, with IKEv1
or with IKEv2.

1. Introduction

This document is a companion to IPsec [RFC2401] and its two key
exchange protocols, IKE [RFC2409] and IKEv2 [IKEv2]. Like most
security protocols, IPsec, IKE, and IKEv2 allow users to chose which
cryptographic algorithms they want to use to meet their security
needs.

Implementation experience with IPsec in manual key mode and with IKE
has shown that there are so many choices for typical system
administrators to make that it is difficult to achieve
interoperability without careful pre-agreement. Because of this, the
IPsec Working Group agreed that there should be a small number of
named suites that cover typical security policies. These suites may
be presented in the administrative interface of the IPsec system.
These suites, often called "UI suites" ("user interface suites"), are
optional and do not prevent implementers from allowing individual
selection of the security algorithms.

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RFC 4308 Cryptographic Suites for IPsec December 2005

Although the UI suites listed here are optional to implement, this
document is on the standards track because implementers who call
particular suites by the names used here have to conform to the
suites listed in this document. These suites should not be
considered extensions to IPsec, IKE, and IKEv2, but instead
administrative methods for describing sets of configurations.

The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as described in [RFC2119].

2. UI Suites

This section lists optional, non-mandatory suites that may be
presented to system administrators to ease the burden of choosing
among the many options in IPsec systems. These suites cannot cover
all of the options that an administrator needs to select. Instead,
they give values for a subset of the options.

Note that these UI suites are simply collections of values for some
options in IPsec. Use of UI suites does not change the IPsec, IKE,
or IKEv2 protocols in any way. Specifically, the transform
substructure in IKE and IKEv2 must be used to give the value for each
specified option regardless of whether or not UI suites are used.

Implementations that use UI suites SHOULD also provide a management
interface for specifying values for individual cryptographic options.
That is, it is unlikely that UI suites are a complete solution for
matching the security policies of many IPsec users, and therefore an
interface that gives a more complete set of options should be used as
well.

IPsec implementations that use these UI suites SHOULD use the suite
names listed here. IPsec implementations SHOULD NOT use names
different than those listed here for the suites that are described,
and MUST NOT use the names listed here for suites that do not match
these values. These requirements are necessary for interoperability.

Note that the suites listed here are for use of IPsec in virtual
private networks. Other uses of IPsec will probably want to define
their own suites and give them different names.

Additional suites can be defined by RFCs. The strings used to
identify UI suites are registered by IANA.

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2.1. Suite "VPN-A"

This suite matches the commonly used corporate VPN security used in
IKEv1 at the time of this document's publication.

IPsec:
Protocol Encapsulating Security Payload (ESP) [RFC2406]
ESP encryption TripleDES in CBC mode [RFC2451]
ESP integrity HMAC-SHA1-96 [RFC2404]

IKE and IKEv2:
Encryption TripleDES in CBC mode [RFC2451]
Pseudo-random function HMAC-SHA1 [RFC2104]
Integrity HMAC-SHA1-96 [RFC2404]
Diffie-Hellman group 1024-bit Modular Exponential (MODP) [RFC2409]

Rekeying of Phase 2 (for IKE) or the CREATE_CHILD_SA (for IKEv2) MUST
be supported by both parties in this suite. The initiator of this
exchange MAY include a new Diffie-Hellman key; if it is included, it
MUST be of type 1024-bit MODP. If the initiator of the exchange
includes a Diffie-Hellman key, the responder MUST include a Diffie-
Hellman key, and it MUST of type 1024-bit MODP.

2.2. Suite "VPN-B"

This suite is what many people expect the commonly used corporate VPN
security that will be used within a few years of the time this
document's publication.

IPsec:
Protocol ESP [RFC2406]
ESP encryption AES with 128-bit keys in CBC mode [AES-CBC]
ESP integrity AES-XCBC-MAC-96 [AES-XCBC-MAC]

IKE and IKEv2:
Encryption AES with 128-bit keys in CBC mode [AES-CBC]
Pseudo-random function AES-XCBC-PRF-128 [AES-XCBC-PRF-128]
Integrity AES-XCBC-MAC-96 [AES-XCBC-MAC]
Diffie-Hellman group 2048-bit MODP [RFC3526]

Rekeying of Phase 2 (for IKE) or the CREATE_CHILD_SA (for IKEv2) MUST
be supported by both parties in this suite. The initiator of this
exchange MAY include a new Diffie-Hellman key; if it is included, it
MUST be of type 2048-bit MODP. If the initiator of the exchange
includes a Diffie-Hellman key, the responder MUST include a Diffie-
Hellman key, and it MUST of type 2048-bit MODP.

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RFC 4308 Cryptographic Suites for IPsec December 2005

2.3. Lifetimes for IKEv1

IKEv1 has two security parameters that do not appear in IKEv2,
namely, the lifetime of the Phase 1 and Phase 2 security associations
(SAs). Systems that use IKEv1 with either the VPN-A or VPN-B suites
MUST use an SA lifetime of 86400 seconds (1 day) for Phase 1 and an
SA lifetime of 28800 seconds (8 hours) for Phase 2.

3. Acknowledgements

Much of the text and ideas in this document came from earlier
versions of the IKEv2 document edited by Charlie Kaufman. Other text
and ideas were contributed by other members of the IPsec Working
Group.

4. Security Considerations

This document inherits all of the security considerations of the
IPsec, IKE, and IKEv2 documents.

Some of the security options specified in these suites may be found
in the future to have properties significantly weaker than those that
were believed at the time this document was produced.

5. IANA Considerations

IANA has created and will maintain a registry called, "Cryptographic
Suites for IKEv1, IKEv2, and IPsec". The registry consists of a text
string and an RFC number that lists the associated transforms. New
entries can be added to the registry only after RFC publication and
approval by an expert designated by the IESG.

The initial values for the new registry are:

Identifier Defined in
VPN-A RFC 4308
VPN-B RFC 4308

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6. Normative References

[AES-CBC] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC
Cipher Algorithm and Its Use with IPsec", RFC
3602, September 2003.

[AES-XCBC-MAC] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96
Algorithm and Its Use With IPsec", RFC 3566,
September 2003.

[AES-XCBC-PRF-128] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for
the Internet Key Exchange Protocol (IKE)", RFC
3664, January 2004.

[IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.

[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
Keyed-Hashing for Message Authentication", RFC
2104, February 1997.

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

[RFC2401] Kent, S. and R. Atkinson, "Security Architecture
for the Internet Protocol", RFC 2401, November
1998.

[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96
within ESP and AH", RFC 2404, November 1998.

[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating
Security Payload (ESP)", RFC 2406, November 1998.

[RFC2409] Harkins, D. and D. Carrel, "The Internet Key
Exchange (IKE)", RFC 2409, November 1998.

[RFC2451] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
Algorithms", RFC 2451, November 1998.

[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential
(MODP) Diffie-Hellman groups for Internet Key
Exchange (IKE)", RFC 3526, May 2003.

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RFC 4308 Cryptographic Suites for IPsec December 2005

Author's Address

Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
USA

EMail: [email protected]

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RFC 4308 Cryptographic Suites for IPsec December 2005

Full Copyright Statement

Copyright (C) The Internet Society (2005).

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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