Suite B Profile for Transport Layer Security (TLS)
draft-salter-rfc5430bis-01
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6460.
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| Authors | Margaret Salter , Russ Housley | ||
| Last updated | 2020-01-21 (Latest revision 2011-09-30) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-salter-rfc5430bis-01
INTERNET-DRAFT M. Salter
Obsoletes: RFC 5430 (if approved) National Security Agency
Intended Status: Informational R. Housley
Vigil Security
September 30, 2011
Suite B Profile for Transport Layer Security (TLS)
<draft-salter-rfc5430bis-01.txt>
Abstract
The United States government has published guidelines for "NSA Suite
B Cryptography" that defines cryptographic algorithm policy for
national security applications. This document defines a profile of
Transport Layer Security (TLS) version 1.2 that is fully compliant
with Suite B.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 2 April 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
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Without obtaining an adequate license from the person(s) controlling
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it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction ...................................................3
2. Conventions Used in This Document ..............................3
3. Suite B Requirements ...........................................4
3.1. Minimum Levels of Security (minLOS).......................4
3.2. Suite B TLS Authentication................................5
4. Suite B Compliance and Interoperability Requirements ...........6
4.1. Acceptable Curves .........................................7
4.2. Certificates ..............................................8
4.3. signature_algorithms Extension ............................8
4.4. CertificateRequest Message ................................8
4.5. CertificateVerify Message .................................9
4.6. ServerKeyExchange Message Signature .......................9
5. Security Considerations ........................................9
6. Acknowledgements ...............................................9
7. IANA Considerations ...........................................10
8. References ....................................................10
8.1. Normative References .....................................10
8.2. Informative References ...................................10
9. Annex: A Transitional Suite B Profile .........................11
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1. Introduction
This document specifies the conventions for using National Security
Agency (NSA) Suite B Cryptography [SuiteB] with the Transport Layer
Security (TLS) protocol and the Datagram Transport Layer Security
(DTLS) protocol.
This document does not define any new cipher suites; instead, it
defines a Suite B compliant profile for use with TLS version 1.2
[RFC5246] or DTLS version 1.2 [4347bis] and the cipher suites defined
in [RFC5289]. This profile uses only Suite B algorithms.
RFC 5430 defined an additional transitional profile for use with TLS
versions 1.0 [RFC2246] and 1.1 [RFC4346] or DTLS version 1.0
[RFC4347] and the cipher suites defined in [RFC4492]. When either
the client or the server does not support TLS version 1.2 and DTLS
version 1.2, the transitional profile can be used to achieve
non-Suite-B-compliant interoperability. The description for the
transitional profile appears in the Annex of this document.
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].
We will use the notation "ECDSA-256" to represent the use of the
ECDSA algorithm with the P-256 curve and the SHA-256 hash function.
Similarly, "ECDSA-384" will represent the use of the ECDSA algorithm
with the P-384 curve and the SHA-384 hash function.
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3. Suite B Requirements
The Fact Sheet on Suite B Cryptography requires key establishment and
authentication algorithms based on Elliptic Curve Cryptography and
encryption using AES [AES]. Suite B algorithms are defined to
support two minimum levels of security: 128 and 192 bits.
In particular, Suite B includes:
Encryption: Advanced Encryption Standard (AES) [AES] --
FIPS 197 (with key sizes of 128 and 256 bits)
Digital Signature: Elliptic Curve Digital Signature Algorithm
(ECDSA) [DSS] - FIPS 186-3 (using the
curves with 256- and 384-bit prime moduli)
Key Exchange: Elliptic Curve Diffie-Hellman (ECDH) - NIST
Special Publication 800-56A [PWKE] (using
the curves with 256- and 384-bit prime moduli)
The two elliptic curves used in Suite B each appear in the literature
under two different names. For sake of clarity, we list both names
below:
Curve NIST name [SECG] name
--------------------------------
P-256 nistp256 secp256r1
P-384 nistp384 secp384r1
The purpose of this document is to specify the requirements for a
Suite B Compliant implementation of TLS (hereafter referred to as
Suite B TLS).
3.1. Minimum Levels of Security (minLOS) for Suite B TLS
Suite B provides 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.
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The following combination of algorithms and key sizes are used in
Suite B TLS:
Suite B Combination 1 Suite B Combination 2
-------------------------------- --------------------------------
AES with 128-bit key in GCM mode AES with 256-bit key in GCM mode
ECDH using the 256-bit prime ECDH using the 384-bit prime
modulus curve P-256 [DSS] modulus curve P-384 [DSS]
TLS PRF with SHA-256 [SHS] TLS PRF with SHA-384 [SHS]
Suite B TLS configured at a minimum level of security of 128 bits
MUST use a TLS cipher suite satisfying either
SuiteB_Combination_1 in its entirety or SuiteB_Combination_2 in its
entirety.
Suite B TLS configured at a minimum level of security of 192 bits
MUST use a TLS cipher suite satisfying SuiteB_Combination_2 in its
entirety.
The specific Suite B compliant cipher suites for each combination are
listed in Section 4.
For Suite B TLS, ECDH uses the Ephemeral Unified Model Scheme with
cofactor set to 1 (see Section 6.1.2.2 in [PWKE]).
To accommodate backward compatibility, a Suite B TLS client or server
MAY be configured to accept a cipher suite that is not part of Suite
B. However, whenever a Suite B TLS client and a Suite B TLS server
establish a TLS version 1.2 session, Suite B algorithms MUST be
employed.
3.2 Suite B TLS Authentication
Suite B TLS MUST use ECDSA for digital signatures; authentication
methods other than ECDSA-256 and ECDSA-384 MUST NOT be used for TLS
authentication. If a relying party receives a signature based on any
other authentication method, it MUST return a TLS error and stop the
TLS handshake.
A system compliant with the Suite B TLS and configured at a minimum
level of security of 128 bits MUST use either ECDSA-256 or ECDSA-384
for client or server authentication. One party can authenticate with
ECDSA-256 when the other party authenticates with ECDSA-384. This
flexibility allows interoperation between a client and a server that
have ECDSA authentication keys of different sizes.
Clients and servers in a system configured at a minimum level of
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security of 128 bits MUST be able to verify ECDSA-256 signatures and
SHOULD be able to verify ECDSA-384 signatures unless it is absolutely
certain that the implementation will never need to verify
certificates originating from an authority which uses an ECDSA-384
signing key.
A system compliant with the Suite B TLS and configured at a minimum
level of security of 192 bits MUST use ECDSA-384 for client and
server authentication.
Clients and servers in a system configured at a minimum level of
security of 192 bits MUST be able to verify ECDSA-384 signatures.
In all cases, the client MUST authenticate the server. The server
MAY authenticate the client, as needed by the specific application.
4. Suite B Compliance and Interoperability Requirements
TLS versions 1.1 [RFC4346] and earlier do not support Galois
CounterMode (GCM) cipher suites [RFC5289]. However, TLS version 1.2
[RFC5246] and later do support GCM. For Suite B TLS, GCM cipher
suites MUST be used, therefore a Suite B TLS client MUST implement
TLS version 1.2 or later.
A Suite B TLS client configured at a minimum level of security of 128
bits MUST offer the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 or the
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 ciphersuite in the
ClientHello message. The TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
ciphersuite is preferred and if offered, MUST appear before the
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 ciphersuite.
If configured at a minimum level of security of 192 bits, the client
MUST offer the TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 ciphersuite
and MUST NOT offer the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
ciphersuite.
One of these two cipher suites MUST be the first (most preferred)
cipher suites in the ClientHello message. A Suite B TLS client that
offers interoperability with non-Suite B compliant servers MAY offer
additional cipher suites, but any additional cipher suites MUST
appear after the two Suite B compliant cipher suites in the
ClientHello message.
A Suite B TLS server MUST implement TLS version 1.2 or later.
A Suite B TLS server configured at a minimum level of security of 128
bits MUST accept either the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
cipher suite or the TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 cipher
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suite if it is offered in the ClientHellomessage, with the
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 cipher suite being preferred.
A Suite B TLS server configured at a minimum security level of 192
bits MUST accept the TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 cipher
suite if it is offered in the ClientHello message.
If the server is not offered either of the Suite B cipher suites and
interoperability with non-Suite B compliant clients is desired, then
the Suite B TLS server MAY accept another offered cipher suite that
is considered acceptable by the server administrator.
4.1. Acceptable Curves
RFC 4492 defines a variety of elliptic curves. Suite B TLS
connections MUST use secp256r1(23) or secp384r1(24). These are the
same curves that appear in FIPS 186-3 [DSS] as P-256 and P-384,
respectively. Secp256r1 MUST be used for the key exchange in all
cipher suites in this specification using AES-128; secp384r1 MUST be
used for the key exchange in all cipher suites in this specification
using AES-256. RFC 4492 requires that the uncompressed(0) form be
supported. The ansiX962_compressed_prime(1) point format MAY also be
supported.
Clients desiring to negotiate only a Suite B TLS connection MUST
generate a "Supported Elliptic Curves Extension" containing only the
allowed curves. Clients operating at a minimum level of security of
128 bits MUST include secp256r1 and SHOULD include secp384r1 in the
extension. Clients operating at a minimum level of security of 192
bits MUST include secp384r1 in the extension. In order to be able to
verify ECDSA signatures, a client and server in a system configured
at a minimum level of security of 128 bits MUST support secp256r1 and
SHOULD support secp384r1 unless it is absolutely certain that the
client and server will never need to use or verify certificates
originating from an authority which uses an ECDSA-384 signing key. A
client and server in a system configured at a minimum level of 192
bits MUST support secp384r1.
TLS connections that offer both Suite B and non-Suite B compliant
options MAY omit the extension or they MAY send the extension but
offer other curves as well as the appropriate Suite B ones.
Servers desiring to negotiate a Suite B TLS connection SHOULD check
for the presence of the extension, but MUST NOT select a non-Suite B
curve even if it is offered by the client. This allows a client that
is willing to do either Suite B or non-Suite B TLS connections to
interoperate with a server that will only do Suite B TLS. If the
client does not advertise an acceptable curve, the server MUST
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generate a fatal "handshake_failure" alert and terminate the
connection. Clients MUST check the chosen curve to make sure that it
is one of the Suite B curves.
4.2. Certificates
Server and client certificates used to establish a Suite B TLS
connection MUST be signed with ECDSA and MUST be compliant with the
"Suite B Certificate and Certificate Revocation List (CRL) Profile",
[RFC5759].
4.3. signature_algorithms Extension
The signature_algorithms extension is defined in Section 7.4.1.4.1 of
TLS version 1.2 [RFC5246]. A Suite B TLS version 1.2 or later client
MUST include the signature_algorithms extension. A Suite B TLS client
configured at a minimum level of security of 128 bits MUST offer
SHA-256 with ECDSA and SHOULD offer ECDSA with SHA-384 in the
signature_algorithms extension unless it is absolutely certain that a
client will never need to use or verify certificates originating from
an authority which uses an ECDSA-384 signing key. A Suite B TLS
client configured at a minimum level of 192 bits MUST offer ECDSA
with SHA-384 in the signature_algorithms extension.
Following the guidance in [RFC5759], Suite B TLS connections MUST
only accept signature algorithms ECDSA with either SHA-256 or SHA-384
for certification path validation. (Note that this is a change from
[RFC5430].)
Other offerings MAY be included to indicate the signature algorithms
that are acceptable in cipher suites that are offered for
interoperability with servers that are not compliant with Suite B and
to indicate the signature algorithms that are acceptable for
certification path validation in non-compliant Suite B TLS
connections.
4.4. CertificateRequest Message
A Suite B TLS server configured at a minimum level of security of 128
bits MUST include ECDSA with SHA-256 and SHOULD include ECDSA with
SHA-384 in the supported_signature_algorithms field of the
CertificateRequest message unless it is absolutely certain that a
server will never need to verify certificates originating from an
authority which uses an ECDSA-384 signing key. A Suite B TLS server
configured at a minimum level of security of 192 bits MUST include
ECDSA with SHA-384 in the supported_signature_algorithms field.
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4.5. CertificateVerify Message
Using the definitions found in section 3.2, a Suite B TLS client MUST
use ECDSA-256 or ECDSA-384 for the signature in the CertificateVerify
message. A Suite B TLS client configured at a minimum level of
security of 128 bits MUST use ECDSA-256 or ECDSA-384. A Suite B TLS
client configured at a minimum level of security of 192 bits MUST use
ECDSA-384.
4.6. ServerKeyExchange Message Signature
In the TLS_ECDHE_ECDSA-collection of cipher suites, the server sends
its ephemeral ECDH public key and a specification of the
corresponding curve in the ServerKeyExchange message. These
parameters MUST be signed with ECDSA using the server's private key,
which corresponds to the public key in the server's certificate.
A Suite B TLS server MUST sign the ServerKeyExchange message using
either ECDSA-256 or ECDSA-384. A system configured at a minimum
level of security of 128 bits MUST use either ECDSA-256 or ECDSA-384.
A system configured at a minimum level of security of 192-bits MUST
use ECDSA-384.
5. Security Considerations
Most of the security considerations for this document are described
in "The Transport Layer Security (TLS) Protocol Version 1.2"
[RFC5246], "Elliptic Curve Cryptography (ECC) Cipher Suites for
Transport Layer Security (TLS)" [RFC4492], "AES Galois Counter Mode
(GCM) Cipher Suites for TLS" [RFC5288], and "TLS Elliptic Curve
Cipher Suites with SHA-256/384 and AES Galois Counter Mode (GCM)"
[RFC5289]. Readers should consult those documents.
In order to meet the goal of a consistent security level for the
entire cipher suite, Suite B TLS implementations MUST ONLY use the
curves defined in Section 4.2. Otherwise, it is possible to have a
set of symmetric algorithms with much weaker or stronger security
properties than the asymmetric (ECC) algorithms.
6. Acknowledgements
The authors would like to thank Eric Rescorla for his work on the
original RFC 5430.
This work was supported by the US Department of Defense.
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7. IANA Considerations
None.
{{{ RFC Editor, please remove this section prior to publication. }}}
8. References
8.1. Normative References
[4347bis] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security version 1.2", draft-ietf-tls-rfc4347-bis, July
2010.
[AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", FIPS 197, November 2001.
[DSS] National Institute of Standards and Technology, "Digital
Signature Standard", FIPS 186-3, June 2009.
[PWKE] National Institute of Standards and Technology,
"Recommendation for Pair-Wise Key Establishment Schemes
Using Discrete Logarithm Cryptography (Revised)", NIST
Special Publication 800-56A, March 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4347] Rescorla, E., and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008.
[RFC5759] Solinas, J. and Zieglar L., "Suite B Certificate and
Certificate Revocation List (CRL) Profile", RFC 5759,
February 2010.
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[SHS] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS 180-3,October 2008.
8.2. Informative References
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246,February 1999.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008.
[RFC5430] Salter, M., Rescorla, E., and R. Housley, "Suite B Profile
for Transport Layer Security (TLS)", RFC 5430, March 2009.
[SECG] Brown, D., "SEC 2: Recommended Elliptic Curve Domain
Parameters",
http://www.secg.org/download/aid-784/sec2-v2.pdf, February
2010.
[SuiteB] National Security Agency, "Fact Sheet NSA Suite B
Cryptography",February 2009,
http://www.nsa.gov/ia/programs/suiteb_cryptography/.
9. Annex: A Transitional Suite B Profile for TLS 1.1 and 1.0
A transitional profile is described for use with TLS version 1.0
[RFC2246], TLS version 1.1 [RFC4346], or DTLS version 1.0 [RFC4347]
and the cipher suites defined in [RFC4492]. This profile uses the
Suite B cryptographic algorithms to the greatest extent possible and
provides backward compatibility. While the transitional profile is
not a Suite B Compliant implementation of TLS, it provides a
transitional path towards the Suite B compliant Profile.
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The following combination of algorithms and key sizes are defined for
use with the Suite B TLS transitional profile:
Transitional Suite B Combination 1 Transitional Suite B Combination 2
---------------------------------- ----------------------------------
AES with 128-bit key in CBC mode AES with 256-bit key in CBC mode
ECDH using the 256-bit prime ECDH using the 384-bit prime
modulus curve P-256 [DSS] modulus curve P-384 [DSS]
Standard TLS PRF Standard TLS PRF
(with SHA-1 and MD5) (with SHA-1 and MD5)
HMAC with SHA-1 for message HMAC with SHA-1 for message
authentication authentication
A Transitional Suite B TLS system configured at a minimum level of
security of 128 bits MUST use a TLS cipher suite satisfying either
Transitional Suite B Combination 1 in its entirety or Transitional
Suite B Combination 2 in its entirety.
A Transitional Suite B TLS system configured at a minimum level of
security of 192 bits MUST use a TLS cipher suite satisfying
Transitional Suite B Combination 2 in its entirety.
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA and
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA satisfy the requirements of
Transitional Suite B Combination 1 and Transitional Suite B
Combination 2, respectively.
A Transitional Suite B TLS client MUST implement TLS version 1.1 or
earlier.
A Transitional Suite B TLS system configured at a minimum level of
security of 128 bits, MUST offer the
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA cipher suite and/or the
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA cipher suite in the
ClientHello message. The TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA cipher
suite is preferred, and if it is offered, it MUST appear before the
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA cipher suite (if present).
A Transitional Suite B TLS system configured at a minimum level of
security of 192 bits MUST offer the
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA cipher suite in the ClientHello
message.
One of these Transitional Suite B cipher suites MUST be the first
(most preferred) in the ClientHello message.
A Transitional Suite B client that offers interoperability with
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non-Suite B transitional servers MAY offer additional cipher suites.
If any additional cipher suites are offered, they MUST appear after
the Transitional Suite B cipher suites in the ClientHello message.
A Transitional Suite B TLS server MUST implement TLS version 1.1 or
earlier.
A Transitional Suite B TLS server configured at a minimum level of
security of 128 bits MUST accept the
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA cipher suite (preferred) or the
TLS_ECHDE_ECDSA_WITH_AES_256_CBC_SHA cipher suite if offered in the
ClientHello message.
A Transitional Suite B TLS server configured at a minimum level of
security of 192 bits MUST accept the
TLS_ECHDE_ECDSA_WITH_AES_256_CBC_SHA cipher suite if offered in the
ClientHello message.
If a Transitional Suite B TLS server is not offered the Transitional
Suite B cipher suites and interoperability with non-Transitional
Suite B clients is desired, then the server MAY accept another
offered cipher suite that is considered acceptable by the server
administrator.
A Transitional Suite B TLS server MUST sign the ServerKeyExchange
message using ECDSA with SHA-1. The Transitional Suite B profile
does not impose any additional restrictions on the server certificate
signature or the signature schemes used elsewhere in the
certification path. Likewise, the Transitional Suite B Profile does
not impose restrictions on signature schemes used in the
certification path for the client's certificate when mutual
authentication is employed.
Authors' Addresses
Margaret Salter
National Security Agency
9800 Savage Rd.
Fort Meade 20755-6709
USA
EMail: msalter@restarea.ncsc.mil
Russ Housley
Vigil Security
918 Spring Knoll Drive
Herndon 21070
USA
EMail: housley@vigilsec.com
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