Network Working Group K.W. Burgin
Internet Draft National Security Agency
Intended Status: Informational M.A. Peck
Expires: January 12, 2012 The MITRE Corporation
July 11, 2011
Suite B Profile for Internet Protocol Security (IPsec)
draft-burgin-ipsec-suiteb-profile-01
Abstract
The United States Government has published guidelines for "NSA
Suite B Cryptography" dated July, 2005, which defines cryptographic
algorithm policy for national security applications. This document
specifies the conventions for using Suite B cryptography in IP
Security (IPsec).
Since many of the Suite B algorithms enjoy uses in other environments
as well, the majority of the conventions needed for the Suite B
algorithms are already specified in other documents. This document
references the source of these conventions, with some relevant
details repeated to aid developers that choose to support Suite B.
Status of this Memo
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This Internet-Draft will expire on January 12, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this Document . . . . . . . . . . . . . . 3
3. Suite B Requirements . . . . . . . . . . . . . . . . . . . . . 4
4. Minimum Levels of Security (minLOS) . . . . . . . . . . . . . 4
4.1. Non-signature Primitives . . . . . . . . . . . . . . . . . 4
4.2. Suite B IPsec Cryptographic Suites . . . . . . . . . . . . 5
4.3. Suite B IKEv2 Authentication . . . . . . . . . . . . . . . 5
4.4. Digital Signatures and Certificates . . . . . . . . . . . 6
5. Suite B Security Associations (SAs) for IKEv2 and IPsec . . . 6
6. The Key Exchange Payload in the IKE_SA_INIT Exchange . . . . . 7
7. Generating Keying Material for the IKE SA . . . . . . . . . . 7
8. Additional Requirements . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1 Normative References . . . . . . . . . . . . . . . . . . . 9
11.2 Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
The Fact Sheet on National Security Agency (NSA) Suite B Cryptography
[NSA] states:
A Cryptographic Interoperability Strategy (CIS) was developed to
find ways to increase assured rapid sharing of information both
within the U.S. and between the U.S. and her partners through the
use of a common suite of public standards, protocols, algorithms
and modes referred to as the "Secure Sharing Suite" or S.3 The
implementation of CIS will facilitate the development of a broader
range of secure cryptographic products which will be available to
a wide customer base. The use of selected public cryptographic
standards and protocols and Suite B is the core of CIS.
In 2005, NSA announced Suite B Cryptography which built upon the
National Policy on the use of the Advanced Encryption Standard
(AES) to Protect National Security Systems and National Security
Information. In addition to the AES algorithm, Suite B includes
cryptographic algorithms for key exchanges, digital signatures and
hashing. Suite B cryptography has been selected from cryptography
that has been approved by NIST for use by the U.S. Government and
specified in NIST standards or recommendations.
IP Security (IPsec) provides confidentiality, data integrity, access
control and data source authentication to IP datagrams. The Internet
Key Exchange (IKE) provides an automated key management for IPsec,
performing mutual authentication between two parties and establishing
security associations (SAs) that protects both IKE and IPsec
communications. Suite B compliant implementations for IPsec MUST use
IKEv2 [RFC5996].
[RFC4869bis] defines a set of four cryptographic user interface
suites for IPsec that are comprised of Suite B algorithms. The four
suites specify options for IKEv2 and for the IP Encapsulating
Security Payload (ESP), [RFC4303]. Suite B compliant implementations
for IPsec MUST use one of these four suites depending upon the
desired security level and security services.
2. 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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3. Suite B Requirements
Suite B requires that key establishment and signature algorithms be
based upon Elliptic Curve Cryptography and that the encryption
algorithm be AES [FIPS197]. Suite B includes [NSA]:
Encryption: Advanced Encryption Standard (AES) (key sizes
of 128 and 256 bits)
Digital Signature Elliptic Curve Digital Signature Algorithm
(ECDSA) [FIPS186-3] (using the curves with 256-
and 384-bit prime moduli)
Key Exchange Elliptic Curve Diffie-Hellman (ECDH)
[SP800-56A], (using the curves with 256- and
384-bit prime moduli)
Hashes SHA-256 and SHA-384 [FIPS180-3]
The two elliptic curves used in Suite B appear in the literature
under two different names. For sake of clarity, we list both names
below:
Curve NIST name SECG name IANA assigned DH group #
-----------------------------------------------------------------
P-256 nistp256 secp256r1 19
P-384 nistp384 secp384r1 20
IANA has already registered these DH groups in [IKEV2IANA].
4. Minimum Levels of Security (minLOS)
Suite B provides for two levels of cryptographic security, namely a
128-bit minimum level of security (minLOS_128) and a 192-bit minimum
level of security (minLOS_192). Each level defines a minimum
strength that all cryptographic algorithms must provide.
4.1. Non-signature Primitives
We divide the Suite B non-signature primitives into two columns as
shown in Table 1.
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Column 1 Column 2
+-------------------+------------------+
Encryption | AES-128 | AES-256 |
+-------------------+------------------+
Key Agreement | ECDH on P-256 | ECDH on P-384 |
+-------------------+------------------+
Hash for PRF/MAC | SHA256 | SHA384 |
+-------------------+------------------+
Table 1: Suite B Cryptographic Non-Signature Primitives
At the 128-bit minimum level of security:
- the non-signature primitives MUST either come exclusively from
Column 1 or exclusively from Column 2.
At the 192-bit minimum level of security:
- the non-signature primitives MUST come exclusively from
Column 2.
4.2. Suite B IPsec Cryptographic Suites
Each system MUST specify a security level of a minimum of 128 bits or
192 bits. The security level determines which suites from
[RFC4869bis] are allowed.
The four Suite B cryptographic user interface (UI) suites,
[RFC4869bis], Suite-B-GCM-128, Suite-B-GMAC-128, Suite-B-GCM-256 or
Suite-B-GMAC-256, satisfy the requirements of section 3.
At the 128-bit minimum level of security:
- one of Suite-B-GCM-128, Suite-B-GMAC-128, Suite-B-GCM-256 or
Suite-B-GMAC-256 MUST be used by Suite B IPsec compliant
implementations [RFC4869bis].
At the 192-bit minimum level of security:
- one of Suite-B-GCM-256 or Suite-B-GMAC-256 MUST be used by
Suite B IPsec compliant implementations [RFC4869bis].
4.3. Suite B IKEv2 Authentication
Digital signatures using ECDSA MUST be used for authentication by
Suite B compliant implementations. [RFC4754] defines two digital
signature algorithms: ECDSA-256 and ECDSA-384. Following the
direction of RFC 4754, ECDSA-256 represents an instantiation of the
ECDSA algorithm using the P-256 curve and the SHA-256 hash function.
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ECDSA-384 represents an instantiation of the ECDSA algorithm using
the P-384 curve and the SHA-384 hash function.
If configured at a minimum level of security of 128 bits, a system
MUST use either ECDSA-256 or ECDSA-384 for IKE authentication. It is
allowable for one party to authenticate with ECDSA-256 and the other
party to authenticate with ECDSA-384. This flexibility will allow
interoperability between an initiator and a responder that have
different sizes of ECDSA authentication keys.
Initiators and responders in a system configured at a minimum level
of security of 128 bits MUST be able to verify ECDSA-256 signatures
and SHOULD be able to verify ECDSA-384 signatures.
If configured at a minimum level of security of 192 bits, ECDSA-384
MUST be used by both parties for IKEv2 authentication.
Initiators and responders in a system configured at a minimum level
of security of 192 bits MUST be able to verify ECDSA-384 signatures.
Authentication methods other than ECDSA-256 and ECDSA-384 MUST NOT be
used for IKEv2 authentication. If a relying party receives a message
signed with any other authentication method, it MUST return an
AUTHENTICATION_FAILED notification and stop processing the message.
4.4. Digital Signatures and Certificates
The initiator and responder, at both minimum levels of security, MUST
each have an X.509 certificate that complies with the "Suite B
Certificate and Certificate Revocation List (CRL) Profile" [RFC5759]
and that contains an elliptic curve public key with the key usage bit
set for digital signature.
5. Suite B Security Associations (SAs) for IKEv2 and IPsec
The four suites in [RFC4869bis] specify options for ESP, [RFC4303],
and IKEv2, [RFC5996]. The four suites are differentiated by
cryptographic algorithm strength and a choice of whether the
Encapsulating Security Payload (ESP) is to provide both
confidentiality and integrity or integrity only. The suite names are
based upon the AES mode ("GCM" or "GMAC") and the AES key length
specified for ESP ("128" or "256"). Suites with "GCM" in their name
MUST be used when ESP integrity protection and encryption are both
needed. Suites with "GMAC" in their name MUST be used only when there
is no need for ESP encryption.
An initiator in a system configured at a minimum level of security of
128 bits MUST offer one or more of the four suites: Suite-B-GCM-128,
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Suite-B-GMAC-128, Suite-B-GCM-256 or Suite-B-GMAC-256 [RFC4869bis].
Suite-B-GCM-128 and Suite-B-GMAC-128, if offered, MUST appear in the
IKEv2 and IPsec SA payloads before any offerings of Suite-B-GCM-256
and Suite-B-GMAC-256.
A responder in a system configured at a minimum level of security of
128 bits MUST support one or both of the two suites Suite-B-GCM-128
or Suite-B-GMAC-128 and SHOULD support one or both of the two suites
Suite-B-GCM-256 or Suite-B-GMAC-256. The responder SHOULD accept the
first Suite B UI suite offered by the initiator that it can
accommodate. If none of the four suites are offered, the responder
MUST return a Notify payload with the error "NO_PROPOSAL_CHOSEN".
An initiator in a system configured at a minimum level of security of
192 bits MUST offer either one or both suites: Suite-B-GCM-256 or
Suite-B-GMAC-256.
A responder configured in a system at a minimum level of security of
192 bits MUST choose one of Suite-B-GCM-256 or Suite-B-GMAC-256. If
neither suite is offered, the responder MUST return a Notify payload
with the error "NO_PROPOSAL_CHOSEN".
6. The Key Exchange Payload in the IKE_SA_INIT Exchange
A Suite B IPsec compliant initiator and responder MUST each generate
an ephemeral elliptic curve key pair to be used in the elliptic curve
Diffie-Hellman (ECDH) key exchange. If the 256-bit random ECP group
for Transform Type 4 is selected, each side MUST generate an EC key
pair using the P-256 elliptic curve, [SP800-57]. If the 384-bit
random ECP group for Transform Type 4 is selected, each side MUST
generate an EC key pair using the P-384 elliptic curve, [SP800-57].
The ephemeral public keys MUST be stored in the key exchange payload
as in [RFC5903].
7. Generating Keying Material for the IKE SA
The elliptic curve Diffie-Hellman shared secret established during
the key exchange consists of the x value of the elliptic curve
Diffie-Hellman common value [RFC5903]. The x value is 256 or 384
bits when using the P-256 or P-384 curve, respectively.
IKEv2, [RFC5996], allows for the reuse of Diffie-Hellman ephemeral
keys. Section 5.6.4.3 of NIST SP800-56A states that an ephemeral
private key MUST be used in exactly one key establishment transaction
and MUST be zeroized after its use. Section 5.8 of SP800-56A states
that the Diffie-Hellman shared secret MUST be zeroized immediately
after its use. Suite B compliant IPsec systems MUST follow the
mandates in SP800-56A.
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If using PRF-HMAC-SHA-256, SKEYSEED, SK_d, SK_pi and SK_pr MUST each
be generated to be 256 bits long per [RFC5996, section 2.14]. If
using PRF-HMAC-SHA-384, SKEYSEED, SK_d, SK_pi and SK_pr MUST each be
generated to be 384 bits long. SK_ai and SK_ar MUST be 256 or 384
bits long if using HMAC-SHA-256-128 or HMAC-SHA-384-192,
respectively. SK_ei and SK_er MUST be 128 or 256 bits long if the key
length attribute for AES_ENC_CBC is set to 128 or 256, respectively.
8. Additional Requirements
AH is not supported in Suite B compliant implementations.
Per [RFC5996], although ESP does not directly include a
Diffie-Hellman exchange, a Diffie-Hellman group MAY be negotiated for
the Child SA. This allows the peers to employ Diffie-Hellman in the
CREATE_CHILD SA exchange. If a transform Type 4 is specified for an
SA for ESP, the value of the transform MUST match that of the
transform used by the IKE SA.
Per RFC 5996, if a CREATE_CHILD_SA exchange includes a KEi payload,
at least one of the SA offers MUST include the Diffie-Hellman group
of the KEi. For Suite B IPsec compliant implementations, the
Diffie-Hellman group of the KEi MUST use the same random ECP group
used in the IKE_INIT_SA.
For IKEv2, rekeying of the CREATE_CHILD_SA MUST be supported by both
parties. The initiator of this exchange MAY include a new
Diffie-Hellman key; if it is included, it MUST use the same random
ECP group used in the IKE_INIT_SA. It the initiator of the exchange
includes a Diffie-Hellman key, the responder MUST include a
Diffie-Hellman key, and it MUST use the same random ECP group.
Suite B IPsec compliant systems MUST support IKEv2 and MUST NOT use
IKEv1 between a Suite B compliant initiator and responder. To
accommodate backward compatibility, a Suite B IPsec compliant system
can be configured to use IKEv1 so long as only IKEv2 is used between
a Suite B compliant initiator and responder. However, when IKEv1 is
being used, the system is not being operated in a Suite B compliant
mode.
IKEv2 does not specify how Identification Payloads (IDi and IDr) in
the IKE_AUTH exchanges are used for policy lookup. The IKEv2
authentication method MUST NOT use the Identification Payloads for
policy lookup. Instead, the authentication method MUST use an
end-entity found in the end-entity certificate provided by the
authenticating party.
The administrative user interface, (UI), for a system that conforms
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to this profile MUST allow the operator to specify a single suite.
If only one suite is specified in the administrative UI, the IKEv2
implementation MUST only offer algorithms for that one suite.
The administrative UI MAY allow the operator to specify more than one
suite; if it allows this, it MUST allow the operator to specify a
preferred order for the suites that are to be offered or accepted.
The preferred order MUST follow the direction provided in section 4.
If more than one suite is specified in the administrative UI, the
IKEv2 implementation MUST only offer algorithms for those suites.
9. Security Considerations
This document discusses security requirements throughout, and it
inherits the security considerations of [RFC4303], [RFC4754],
[RFC5759], and [RFC5996].
10. IANA Considerations
None.
11. References
11.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4754] Fu, D. and J. Solinas, "IKE and IKEv2 Authentication
Using the Elliptic Curve Digital Signature Algorithm
(ECDSA)", RFC 4754, January 2007.
[RFC4869bis] Law, L. and J. Solinas, "Suite B Cryptographic Suites
for IPsec", draft-law-rfc4869bis-01, February 2011.
[RFC5759] Solinas, J. and L. Zieglar, "Suite B Certificate and
Certificate Revocation List (CRL) Profile", RFC 5759,
January 2010.
[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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[FIPS180-3] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-3, October 2008.
[FIPS186-3] National Institute of Standards and Technology,
"Digital Signature Standard (DSS)", FIPS PUB 186-3,
June 2009.
[FIPS197] National Institute of Standards and Technology,
"Advanced Encryption Standard (AES)", FIPS PUB 197,
November 2001.
11.2 Informative References
[IKEV2IANA] "Internet Key Exchange Version 2 (IKEv2) Parameters",
<http://www.iana.org>.
[NSA] U.S. National Security Agency, "Fact Sheet NSA Suite B
Cryptography", January 2009,
[http://www.nsa.gov/ia/programs/suiteb_cryptography/].
[RFC5903] Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
Prime (ECP Groups) for IKE and IKEv2", RFC 5903, June
2010.
[SP800-56A] National Institute of Standards and Technology,
"Recommendation for Pair-wise Key Establishment Schemes
Using Discrete Logarithm Cryptography", NIST Special
Publication 800-56A, March 2007.
[SP800-57] National Institute of Standards and Technology,
"Recommendation for Key Management - Part 1", NIST
Special Publication 800-57, March 2007.
Authors' Addresses
Kelley W. Burgin
National Security Agency
EMail: kwburgi@tycho.ncsc.mil
Michael A. Peck
The MITRE Corporation
EMail: mpeck@mitre.org
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