Network Working Group D. Cooley
Internet-Draft NSA
Intended status: Informational August 15, 2019
Expires: February 16, 2020

Commercial National Security Algorithm (CNSA) Suite Profile for TLS and DTLS 1.2 and 1.3
draft-cooley-cnsa-dtls-tls-profile-00

Abstract

This document defines a base profile for TLS protocol versions 1.2 and 1.3, as well as DTLS protocol versions 1.2 and 1.3 for use with the United States Commercial National Security Algorithm (CNSA) Suite.

The profile applies to the capabilities, configuration, and operation of all components of US National Security Systems that use TLS or DTLS. It is also appropriate for all other US Government systems that process high-value information.

The profile is made publicly available here for use by developers and operators of these and any other system deployments.

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 https://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 February 16, 2020.

Copyright Notice

Copyright (c) 2019 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

1. Introduction

This document specifies a profile of TLS version 1.2 [RFC5246] and TLS version 1.3 [RFC8446], as well as DTLS version 1.2 [RFC6347] and DTLS version 1.3 [ID.dtls13] for use by applications that support the National Security Agency's (NSA) Commercial National Security Algorithm (CNSA) Suite [CNSA]. The profile applies to the capabilities, configuration, and operation of all components of US National Security Systems [SP80059]. It is also appropriate for all other US Government systems that process high-value information. It is made publicly available for use by developers and operators of these and any other system deployments.

This document does not define any new cipher suites; instead, it defines a CNSA compliant profile of TLS and DTLS, and the cipher suites defined in [RFC5288] and [RFC5289]. This profile uses only algorithms in the CNSA Suite.

The reader is assumed to have familiarity with the TLS 1.2 and 1.3 as well as the DTLS 1.2 and 1.3 protocol specifications: [RFC5246], [RFC6347], [RFC8446], and [ID.dtls13]. All MUST-level requirements from the protocol documents apply throughout this profile; they are generally not repeated. This profile contains changes that elevate some SHOULD-level options to MUST-level; this profile also contains changes that elevate some MAY-level options to SHOULD-level or MUST-level. All options that are not mentioned in this profile remain at their original requirement level.

2. The Commercial National Security Algorithm Suite

The National Security Agency (NSA) profiles commercial cryptographic algorithms and protocols as part of its mission to support secure, interoperable communications for US Government National Security Systems. To this end, it publishes guidance both to assist with the US Government transition to new algorithms, and to provide vendors - and the Internet community in general - with information concerning their proper use and configuration.

Recently, cryptographic transition plans have become overshadowed by the prospect of the development of a cryptographically-relevant quantum computer. NSA has established the CNSA Suite to provide vendors and IT users near-term flexibility in meeting their Information Assurance (IA) interoperability requirements. The purpose behind this flexibility is to avoid having vendors and customers make two major transitions in a relatively short timeframe, as we anticipate a need to shift to quantum-resistant cryptography in the near future.

NSA is authoring a set of RFCs, including this one, to provide updated guidance concerning the use of certain commonly available commercial algorithms in IETF protocols. These RFCs can be used in conjunction with other RFCs and cryptographic guidance (e.g., NIST Special Publications) to properly protect Internet traffic and data-at-rest for US Government National Security Systems.

3. Terminology

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.

"ECDSA" and "ECDH" refer to the use of the Elliptic Curve Digital Signature Algorithm (ECDSA) and Elliptic Curve Diffie Hellman (ECDH), respectively. ECDSA and ECDH are used with the NIST P-384 curve (which is based on a 384-bit prime modulus) and the SHA-384 hash function. Similarly, "RSA" and "DH" refer to Rivest-Shamir-Adleman (RSA) and Finite Field Diffie-Hellman (DH), respectively. RSA and DH are used with a 3072-bit or 4096-bit modulus. When RSA is used for digital signature, it is used with the SHA-384 hash function.

Henceforth, this document refers to TLS versions 1.2 and 1.3 and DTLS versions 1.2 and 1.3 collectively as (D)TLS.

4. CNSA Suite

[CNSA] approves the use of both finite field and elliptic curve versions of the DH key agreement algorithm, as well as RSA-based key establishment. [CNSA] also approves certain versions of the RSA and elliptic curve digital signature algorithms. The approved encryption techniques include the Advanced Encryption Standard (AES) used with a 256-bit key in an Authenticated Encryption with Associated Data (AEAD) mode.

In particular, CNSA includes the following:

[CNSA] also approves the use of SHA-384 [SHS] for the hash algorithm for mask generation, signature generation, Pseudo Random Function (PRF) in TLS 1.2 and HMAC-based key derivation function (HKDF) in TLS 1.3.

4.1. CNSA (D)TLS Key Establishment Algorithms

The following combination of algorithms and key sizes are used in CNSA (D)TLS:

Or

Or

The specific CNSA compliant cipher suites are listed in Section 5.

4.2. CNSA TLS Authentication

For server and/or client authentication, CNSA (D)TLS MUST generate and verify either ECDSA signatures or RSA signatures.

In all cases, the client MUST authenticate the server. The server MAY also authenticate the client, as needed by the specific application.

5. CNSA Compliance and Interoperability Requirements

CNSA (D)TLS MUST NOT use TLS versions prior to (D)TLS 1.2 in a CNSA compliant system. CNSA (D)TLS servers and clients MUST implement and use either (D)TLS version 1.2 [RFC5246][RFC6347] or (D)TLS version 1.3 [RFC8446][ID.dtls13].

5.1. Acceptable ECC Curves

The elliptic curves used in the CNSA Suite appear in the literature under two different names [DSS] [SECG]. For the sake of clarity, both names are listed below:

      Curve    NIST name   SECG name
      --------------------------------
      P-384    nistp384    secp384r1

[RFC8422] defines a variety of elliptic curves. CNSA (D)TLS connections MUST use secp384r1(24) (also called nistp384) and the uncompressed(0) form MUST be supported, as required by [RFC8422] and [RFC8446].

Key pairs MUST be generated following Section 5.6.1.2 of [PWKE-A].

5.2. Acceptable RSA Schemes, Parameters and Checks

[CNSA] specifies a minimum modulus size of 3072 bits; however, only two modulus sizes (3072 bits and 4096 bits) are supported by this profile.

For authentication, RSASSA-PKCS1-v1.5 [RFC8017] MUST be supported, and RSASSA-PSS [DSS] SHOULD be supported.

For key transport, RSAES-PKCS1-v1.5 [RFC8017] MUST be supported.

RSA exponent e MUST satisfy 2^16<e<2^256 and be odd per [DSS].

If RSASSA-PSS is supported, then the implementation MUST assert rsaEncryption as the public key algorithm, the hash algorithm (used for both mask generation and signature generation) MUST be SHA-384, the mask generation function 1 (MGF1) from [RFC8017] MUST be used, and the salt length MUST be 48 octets.

5.3. Acceptable Finite Field Groups

[CNSA] specifies a minimum modulus size of 3072 bits; however, only two modulus sizes (3072 bits and 4096 bits) are supported by this profile.

Ephemeral key pairs MUST be generated following Section 5.6.1.1.1 of [PWKE-A] using the approved safe prime groups specified in [RFC7919] for DH ephemeral key agreement. The named groups are:

5.4. Certificates

Certificates used to establish a CNSA (D)TLS connection MUST be signed with ECDSA or RSA and MUST be compliant with the "CNSA Certificate and Certificate Revocation List (CRL) Profile" [RFC8603].

6. (D)TLS 1.2 Requirements

The CNSA (D)TLS 1.2 client MUST offer at least one of these ciphersuites:

The CNSA cipher suites listed above MUST be the first (most preferred) cipher suites in the ClientHello message.

A CNSA (D)TLS client that offers interoperability with servers that are not CNSA compliant MAY offer additional cipher suites, but any additional cipher suites MUST appear after the CNSA cipher suites in the ClientHello message.

A CNSA (D)TLS server MUST accept one of the CNSA suites above if they are offered in the ClientHello message.

6.1. The signature_algorithms Extension

A CNSA (D)TLS client MUST include the "signature_algorithms" extension. A CNSA (D)TLS client MUST offer a "signature_algorithms" extension with either signature=ecdsa and hash=SHA384 or signature=rsa and hash=sha384.

Following the guidance in [RFC8603], CNSA (D)TLS servers MUST only accept ECDSA or RSA for certification path validation.

Other offerings MAY be included to indicate the acceptable signature algorithms in cipher suites that are offered for interoperability with servers not compliant with CNSA and to indicate the signature algorithms that are acceptable for certification path validation in non-compliant CNSA (D)TLS connections.

6.2. The CertificateRequest Message

A CNSA (D)TLS server MUST include ECDSA and SHA-384 and/or RSA and SHA-384 in the supported_signature_algorithms field.

6.3. The CertificateVerify Message

A CNSA (D)TLS server MUST use ECDSA or RSA in the CertificateVerify message. A CNSA (D)TLS client MUST use ECDSA or RSA.

6.4. The Signature in the ServerKeyExchange Message

A CNSA (D)TLS server MUST sign the ServerKeyExchange message using ECDSA or RSA.

6.5. Certificate Status

The client SHOULD request and the server SHOULD provide OSCP responses in the "CertificateEntry".

7. (D)TLS 1.3

The CNSA (D)TLS client MUST offer the following CipherSuite in the ClientHello:

The CNSA (D)TLS client MUST offer at least one of the following values in the "signature_algorithms" and "signature_algorithms_cert" (optional) extensions:

And, if supported, SHOULD offer:

The CNSA (D)TLS client MUST include at least one of the following values in "supported_groups":

The CNSA cipher suite MUST be the first (most preferred) cipher suites in the ClientHello message and in the extensions.

A CNSA (D)TLS client that offers interoperability with servers that are not CNSA compliant MAY offer additional cipher suites, but any additional cipher suites MUST appear after the CNSA compliant cipher suites in the ClientHello message.

A CNSA (D)TLS server MUST accept one of the CNSA algorithms listed above if they are offered in the ClientHello message.

7.1. The "signature_algorithms" and "signature_algorithms_cert" Extensions

A CNSA (D)TLS client MUST include the "signature_algorithms" extension. A CNSA (D)TLS client MAY include the "signature_algorithms_cert" extension. A CNSA (D)TLS client MUST offer ECDSA with SHA-384 and/or RSA with SHA-384 in the "signature_algorithms" and "signature_algorithm_cert" extensions.

Following the guidance in [RFC8603], CNSA (D)TLS servers MUST only accept ECDSA or RSA for signature path validation.

Other offerings MAY be included to indicate the acceptable signature algorithms in cipher suites that are offered for interoperability with servers not compliant with CNSA and to indicate the signature algorithms that are acceptable for certification path validation in non-compliant CNSA (D)TLS connections.

7.2. The "early_data" Extension

A CNSA (D)TLS client or server MUST NOT include the "early_data" extension. See Section 2.3 [RFC8446] for security concerns.

7.3. Resumption

A CNSA (D)TLS server MAY send a CNSA (D)TLS client a NewSessionTicket extension to enable resumption. A CNSA (D)TLS client MUST request "psk_dhe_ke" via the psk_key_exchange_modes ClientHello extension to resume a session. A CNSA (D)TLS client MUST offer ECDHE with SHA-384, RSA with SHA-384 and/or DHE with SHA-384 in the "psk_key_exchange_modes" extension.

7.4. Certificate Status

The client SHOULD request and the server SHOULD provide OCSP responses in the "CertificateEntry".

8. Security Considerations

Most of the security considerations for this document are described in [RFC5246], [RFC8446], [RFC6347], and [ID.dtls13]. In addition, the security consideration for ECC related to TLS are described in [RFC8422], [RFC5288] and [RFC5289]. Readers should consult those documents.

In order to meet the goal of a consistent security level for the entire cipher suite, CNSA (D)TLS implementations MUST only use the Elliptic Curves, RSA schemes and Finite Fields defined in Section 5.1, Section 5.2, and Section 5.3. Otherwise, it is possible to have a set of symmetric algorithms with much weaker security properties than the asymmetric algorithms.

As noted in TLS version 1.3 [RFC8446], TLS does not provide inherent replay protections for early data. For this reason, this profile forbids the use of early data.

9. IANA Considerations

This document has no IANA actions.

10. References

10.1. Normative References

[AES] National Institute of Standards and Technology, "Specification for the Advanced Encryption Standard (AES)", FIPS 197, November 2001.
[CNSA] Committee for National Security Systems, "Use of Public Standards for Secure Information Sharing", CNSSP 15, October 2016.
[DSS] National Institute of Standards and Technology, "Digital Signature Standard (DSS)", NIST Federal Information Processing Standard 186-4, July 2013.
[GCM] National Institute of Standards and Technology, "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", NIST Special Publication 800-38D, November 2007.
[ID.dtls13] Rescorla, E., Tschofenig, H. and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", March 2019.

Work in progress.

[PWKE-A] National Institute of Standards and Technology, "Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography", NIST Special Publication 800-56A, Revision 3, April 2018.
[PWKE-B] National Institute of Standards and Technology, "Recommendation for Pair-Wise Key Establishment Schemes Using Integer Factorization Cryptography", NIST Special Publication 800-56B, Revision 2, March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A. and D. McGrew, "AES Galois Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, DOI 10.17487/RFC5288, August 2008.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289, DOI 10.17487/RFC5289, August 2008.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012.
[RFC6961] Pettersen, Y., "The Transport Layer Security (TLS) Multiple Certificate Status Request Extension", RFC 6961, DOI 10.17487/RFC6961, June 2013.
[RFC7919] Gillmor, D., "Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for Transport Layer Security (TLS)", RFC 7919, DOI 10.17487/RFC7919, August 2016.
[RFC8017] Moriarty, K., Kaliski, B., Jonsson, J. and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, November 2016.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8422] Nir, Y., Josefsson, S. and M. Pegourie-Gonnard, "Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS) Versions 1.2 and Earlier", RFC 8422, DOI 10.17487/RFC8422, August 2018.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018.
[RFC8603] Jenkins, M. and L. Zieglar, "Commercial National Security Algorithm (CNSA) Suite Certificate and Certificate Revocation List (CRL) Profile", RFC 8603, DOI 10.17487/RFC8603, May 2019.
[SHS] National Institute of Standards and Technology, "Secure Hash Standard (SHS)", NIST Federal Information Processing Standard 180-4, August 2015.

10.2. Informative References

[SECG] Brown, D., "SEC 2: Recommended Elliptic Curve Domain Parameters", February 2010.
[SP80059] National Institute of Standards and Technology, "Guideline for Identifying an Information System as a National Security System", Special Publication 800 59, August 2003.

Author's Address

Dorothy Cooley National Security Agency EMail: decoole@nsa.gov