ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites for TLS 1.2 and DTLS 1.2
Four TLS 1.2 and DTLS 1.2 cipher suites that pair a pre-shared key with ephemeral elliptic-curve key exchange and AEAD encryption.
Mattsson, J. and D. Migault, "ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites for TLS 1.2 and DTLS 1.2", RFC 8442, DOI 10.17487/RFC8442, September 2018, <https://www.rfc-editor.org/info/rfc8442>.
@misc{rfc8442,
series = {Request for Comments},
number = 8442,
howpublished = {RFC 8442},
publisher = {RFC Editor},
doi = {10.17487/RFC8442},
url = {https://www.rfc-editor.org/info/rfc8442},
author = {J. Mattsson and D. Migault},
title = {{ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites for TLS 1.2 and DTLS 1.2}},
pagetotal = 7,
year = 2018,
month = sep,
} RFC text
Contents
Internet Engineering Task Force (IETF) J. Mattsson
Request for Comments: 8442 D. Migault
Category: Standards Track Ericsson
ISSN: 2070-1721 September 2018
ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites
for TLS 1.2 and DTLS 1.2
Abstract
This document defines several new cipher suites for version 1.2 of
the Transport Layer Security (TLS) protocol and version 1.2 of the
Datagram Transport Layer Security (DTLS) protocol. These cipher
suites are based on the Ephemeral Elliptic Curve Diffie-Hellman with
Pre-Shared Key (ECDHE_PSK) key exchange together with the
Authenticated Encryption with Associated Data (AEAD) algorithms
AES-GCM and AES-CCM. PSK provides light and efficient
authentication, ECDHE provides forward secrecy, and AES-GCM and
AES-CCM provide encryption and integrity protection.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8442.
Copyright Notice
Copyright (c) 2018 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 ....................................................2
2. Requirements Notation ...........................................3
3. ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites ................3
4. IANA Considerations .............................................4
5. Security Considerations .........................................4
6. References ......................................................5
6.1. Normative References .......................................5
6.2. Informative References .....................................6
Acknowledgements ...................................................7
Authors' Addresses .................................................7
1. Introduction
This document defines new cipher suites that provide Pre-Shared Key
(PSK) authentication, Perfect Forward Secrecy (PFS), and
Authenticated Encryption with Associated Data (AEAD). The cipher
suites are defined for version 1.2 of the Transport Layer Security
(TLS) protocol [RFC5246] and version 1.2 of the Datagram Transport
Layer Security (DTLS) protocol [RFC6347].
PSK authentication is widely used in many scenarios. One deployment
is 3GPP networks where pre-shared keys are used to authenticate both
subscriber and network. Another deployment is Internet of Things
where PSK authentication is often preferred for performance and
energy efficiency reasons. In both scenarios, the endpoints are
owned and/or controlled by a party that provisions the pre-shared
keys and makes sure that they provide a high level of entropy.
Perfect Forward Secrecy (PFS) is a strongly recommended feature in
security protocol design and can be accomplished by using an
ephemeral Diffie-Hellman key exchange method. Ephemeral Elliptic
Curve Diffie-Hellman (ECDHE) provides PFS with excellent performance
and small key sizes. ECDHE is mandatory to implement in both HTTP/2
[RFC7540] and the Constrained Application Protocol (CoAP) [RFC7252].
AEAD algorithms that combine encryption and integrity protection are
strongly recommended for (D)TLS [RFC7525], and TLS 1.3 [RFC8446]
forbids the use of non-AEAD algorithms. The AEAD algorithms
considered in this document are AES-GCM and AES-CCM. The use of
AES-GCM in TLS is defined in [RFC5288], and the use of AES-CCM is
defined in [RFC6655].
[RFC4279] defines PSK cipher suites for TLS but does not consider
elliptic curve cryptography. [RFC8422] introduces elliptic curve
cryptography for TLS but does not consider PSK authentication.
[RFC5487] describes the use of AES-GCM in combination with PSK
authentication but does not consider ECDHE. [RFC5489] describes the
use of PSK in combination with ECDHE but does not consider AES-GCM or
AES-CCM.
2. Requirements 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. ECDHE_PSK with AES-GCM and AES-CCM Cipher Suites
The cipher suites defined in this document are based on the following
AES-GCM and AES-CCM AEAD algorithms: AEAD_AES_128_GCM [RFC5116],
AEAD_AES_256_GCM [RFC5116], AEAD_AES_128_CCM [RFC5116], and
AEAD_AES_128_CCM_8 [RFC6655].
Messages and premaster secret construction in this document are
defined in [RFC5489]. The ServerKeyExchange and ClientKeyExchange
messages are used, and the premaster secret is computed as for the
ECDHE_PSK key exchange. The elliptic curve parameters used in the
Diffie-Hellman parameters are negotiated using extensions defined in
[RFC8422].
For TLS 1.2 and DTLS 1.2, the following cipher suites are defined:
TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256 = {0xD0,0x01}
TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384 = {0xD0,0x02}
TLS_ECDHE_PSK_WITH_AES_128_CCM_8_SHA256 = {0xD0,0x03}
TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256 = {0xD0,0x05}
The assigned code points can only be used for TLS 1.2 and DTLS 1.2.
The cipher suites defined in this document MUST NOT be negotiated for
any version of (D)TLS other than version 1.2. Servers MUST NOT
select one of these cipher suites when selecting a (D)TLS version
other than version 1.2. A client MUST treat the selection of these
cipher suites in combination with a different version of (D)TLS as an
error and generate a fatal 'illegal_parameter' TLS alert.
Cipher suites TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384,
TLS_AES_128_CCM_8_SHA256, and TLS_AES_128_CCM_SHA256 are used to
support equivalent functionality in TLS 1.3 [RFC8446].
4. IANA Considerations
This document defines the following new cipher suites for TLS 1.2 and
DTLS 1.2. The values have been assigned in the "TLS Cipher Suites"
registry defined by [RFC8446] and [RFC8447].
Value Description DTLS-OK Recommended
----- ----------- ------- -----------
{0xD0,0x01} TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256 Y Y
{0xD0,0x02} TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384 Y Y
{0xD0,0x03} TLS_ECDHE_PSK_WITH_AES_128_CCM_8_SHA256 Y N
{0xD0,0x05} TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256 Y Y
5. Security Considerations
The security considerations in TLS 1.2 [RFC5246], DTLS 1.2 [RFC6347],
PSK Ciphersuites for TLS [RFC4279], ECDHE_PSK [RFC5489], AES-GCM
[RFC5288], and AES-CCM [RFC6655] apply to this document as well.
All the cipher suites defined in this document provide
confidentiality, mutual authentication, and forward secrecy. The
AES-128 cipher suites provide 128-bit security, and the AES-256
cipher suites provide at least 192-bit security. However,
AES_128_CCM_8 only provides 64-bit security against message forgery.
The pre-shared keys used for authentication MUST have a security
level equal to or higher than the cipher suite used, i.e., at least
128-bit security for the AES-128 cipher suites and at least 192-bit
security for the AES-256 cipher suites.
GCM or CCM encryption that reuses a nonce with a same key undermines
the security of GCM and CCM. As a result, GCM and CCM MUST only be
used with a system guaranteeing nonce uniqueness [RFC5116].
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>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<https://www.rfc-editor.org/info/rfc4279>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[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,
<https://www.rfc-editor.org/info/rfc5288>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012,
<https://www.rfc-editor.org/info/rfc6655>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc8422>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
6.2. Informative References
[RFC5487] Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
256/384 and AES Galois Counter Mode", RFC 5487,
DOI 10.17487/RFC5487, March 2009,
<https://www.rfc-editor.org/info/rfc5487>.
[RFC5489] Badra, M. and I. Hajjeh, "ECDHE_PSK Cipher Suites for
Transport Layer Security (TLS)", RFC 5489,
DOI 10.17487/RFC5489, March 2009,
<https://www.rfc-editor.org/info/rfc5489>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>.
Acknowledgements
The authors would like to thank Ilari Liusvaara, Eric Rescorla, Dan
Harkins, Russ Housley, Dan Harkins, Martin Thomson, Nikos
Mavrogiannopoulos, Peter Dettman, Xiaoyin Liu, Joseph Salowey, Sean
Turner, Dave Garrett, Martin Rex, and Kathleen Moriarty for their
valuable comments and feedback.
Authors' Addresses
John Mattsson
Ericsson AB
SE-164 80 Stockholm
Sweden
Phone: +46 76 115 35 01
Email: john.mattsson@ericsson.com
Daniel Migault
Ericsson
8400 Boulevard Decarie
Montreal, QC H4P 2N2
Canada
Phone: +1 514-452-2160
Email: daniel.migault@ericsson.com
AI ELI5
On this page
§1Why These Cipher Suites
The document defines cipher suites that provide pre-shared key (PSK) authentication, perfect forward secrecy (PFS) and authenticated encryption with associated data (AEAD). They are defined for TLS 1.2 (RFC 5246) and DTLS 1.2 (RFC 6347).
The RFC says PSK authentication is widely used. It names 3GPP networks, where pre-shared keys authenticate both subscriber and network, and the Internet of Things, where PSK is often preferred for performance and energy efficiency. In both cases the endpoints are owned or controlled by a party that provisions keys with a high level of entropy.
Some gadgets already share a secret with the server. They still want a fresh secret every time they talk, in case someone steals the old one later.
§1The Gap in Earlier Specifications
Each earlier document covered only part of the combination. RFC 4279 defines PSK cipher suites but not elliptic curves. RFC 8422 adds elliptic curves but not PSK. RFC 5487 combines AES-GCM with PSK but has no ECDHE. RFC 5489 combines PSK with ECDHE but has no AES-GCM or AES-CCM.
ECDHE gives PFS with excellent performance and small key sizes, and it is mandatory to implement in HTTP/2 and CoAP. AEAD algorithms are strongly recommended for TLS and DTLS, and TLS 1.3 forbids non-AEAD algorithms.
Each older recipe had some of the ingredients, but none had all three: the shared secret, the fresh secret and the strong lock.
§3How the Suites Are Built
The suites use four AEAD algorithms: AEAD_AES_128_GCM, AEAD_AES_256_GCM, AEAD_AES_128_CCM and AEAD_AES_128_CCM_8.
Message and premaster secret construction follow RFC 5489. The ServerKeyExchange and ClientKeyExchange messages are used, and the premaster secret is computed as for the ECDHE_PSK key exchange. The elliptic curve parameters are negotiated with the extensions from RFC 8422.
The suites reuse the existing handshake recipe and just swap in modern locks to protect the messages.
§3The Four Cipher Suites
Four suites are defined, with code points in the 0xD0 range: TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256, TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384, TLS_ECDHE_PSK_WITH_AES_128_CCM_8_SHA256 and TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256.
All four are marked DTLS-OK. The IANA table marks all except the CCM_8 suite as Recommended.
There are four ready-made recipes with different lock sizes. The one with the small lock is not recommended.
- {0xD0,0x01}TLS_ECDHE_PSK_WITH_AES_128_GCM_SHA256 — DTLS-OK: Y, Recommended: Y.
- {0xD0,0x02}TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384 — DTLS-OK: Y, Recommended: Y.
- {0xD0,0x03}TLS_ECDHE_PSK_WITH_AES_128_CCM_8_SHA256 — DTLS-OK: Y, Recommended: N.
- {0xD0,0x05}TLS_ECDHE_PSK_WITH_AES_128_CCM_SHA256 — DTLS-OK: Y, Recommended: Y.
§3TLS 1.2 Only
The assigned code points can only be used for TLS 1.2 and DTLS 1.2. The suites MUST NOT be negotiated for any other version of (D)TLS, and servers MUST NOT select one of them when choosing another version.
A client MUST treat such a selection as an error and generate a fatal illegal_parameter alert. For TLS 1.3, the suites TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384, TLS_AES_128_CCM_8_SHA256 and TLS_AES_128_CCM_SHA256 support equivalent functionality.
These recipes only work for one version of the handshake. If a server picks one for the wrong version, the client stops the conversation.
§5Security Considerations
The security considerations of TLS 1.2, DTLS 1.2, PSK ciphersuites, ECDHE_PSK, AES-GCM and AES-CCM all apply. All the suites provide confidentiality, mutual authentication and forward secrecy. The AES-128 suites provide 128-bit security and the AES-256 suites provide at least 192-bit security. However, AES_128_CCM_8 only provides 64-bit security against message forgery.
The pre-shared keys MUST have a security level equal to or higher than the suite used: at least 128-bit for AES-128 suites and at least 192-bit for AES-256 suites. GCM and CCM MUST only be used with a system guaranteeing nonce uniqueness, because reusing a nonce with the same key undermines their security.
A lock is only as good as the key. The shared secret must be at least as strong as the lock, and you must never reuse a one-time number.
§4IANA Registrations
The four values were assigned in the TLS Cipher Suites registry defined by RFC 8446 and RFC 8447. They are {0xD0,0x01}, {0xD0,0x02}, {0xD0,0x03} and {0xD0,0x05}.
Each recipe gets its own number in the official list so both sides can name the one they want.