Internet-Draft draft-denis-tls-aegis-01 December 2023
Denis & Lucas Expires 9 June 2024 [Page]
Workgroup:
Transport Layer Security
Internet-Draft:
draft-denis-tls-aegis-01
Published:
Intended Status:
Informational
Expires:
Authors:
F. Denis
Fastly Inc.
S. Lucas
Individual Contributor

AEGIS-based Cipher Suites for TLS 1.3, DTLS 1.3 and QUIC

Abstract

This documents proposes new cipher suites based on the AEGIS family of authenticated encryption algorithms for integration into the TLS 1.3, DTLS 1.3, and QUIC protocols.

About This Document

This note is to be removed before publishing as an RFC.

Status information for this document may be found at https://datatracker.ietf.org/doc/draft-denis-tls-aegis/.

Source for this draft and an issue tracker can be found at https://github.com/jedisct1/draft-denis-tls-aegis.

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 9 June 2024.

1. Introduction and rationale

AEGIS [I-D.irtf-cfrg-aegis-aead] is a family of authenticated encryption algorithms designed for high-performance applications. AEGIS caters to the same hardware class as AES-GCM, distinguishing itself through the following key attributes:

  1. Reduced memory requirements: AEGIS eliminates the necessity for a key schedule and precomputation tables, resulting in lower memory demands. This characteristic proves particularly advantageous for servers managing a substantial volume of connections.

  2. Extended usage limits: AEGIS features higher usage limits, mitigating the need for frequent rekeying compared to other available options.

  3. Enhanced overall performance: AEGIS is very efficient on CPUs supporting AES-specific instructions.

AEGIS ciphers seamlessly integrate into established protocols like TLS 1.3 by adhering to the same interface standards as existing algorithms.

This document introduces new cipher suites based on the AEGIS algorithms and outlines the procedures for their incorporation into the TLS 1.3 [RFC8446], DTLS 1.3 [RFC9147], and QUIC [RFC9000] protocols.

2. Conventions and Definitions

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. New Cipher Suites and Preservation of TLS 1.3 Mechanisms

The TLS 1.3 protocol includes a set of mandatory cipher suites listed in [RFC8446], Section 9.1.

Each cipher suite denotes the Authenticated Encryption with Associated Data (AEAD) algorithm for record protection, along with the designated hash algorithm for use with the HMAC-based Key Derivation Function (HKDF).

The cipher suites and cryptographic negotiation mechanisms established in TLS 1.3 are reused by the DTLS 1.3 and QUIC protocols.

To accommodate AEGIS-based encryption algorithms, this document introduces additional cipher suites to those specified in [RFC8446], Section 9.1:

Table 1: Proposed AEGIS-based cipher suites
Cipher Suite Name AEAD Algorithm Hash Algorithm Confidentiality Level
TLS_AEGIS_128L_SHA256 AEGIS-128L SHA256 128 bits
TLS_AEGIS_128X2_SHA256 AEGIS-128X2 SHA256 128 bits
TLS_AEGIS_256_SHA512 AEGIS-256 SHA512 256 bits
TLS_AEGIS_256X2_SHA512 AEGIS-256X2 SHA512 256 bits

The rationale behind recommending the SHA512 hash function for variants employing a 256-bit key is based on the findings presented in [M23].

AEGIS algorithms support both 128-bit and 256-bit authentication tags. For all the cipher suites referenced herein, these algorithms MUST be utilized with a 128-bit authentication tag.

With the inclusion of these new cipher suites, the cryptographic negotiation mechanism in TLS 1.3, as outlined in [RFC8446], Section 4.1.1, remains unchanged, as does the record payload protection mechanism specified in [RFC8446], Section 5.2.

4. DTLS 1.3 Record Number Encryption

In DTLS 1.3, encryption of record sequence numbers follows the specifications detailed in [RFC9147], Section 4.2.3.

For AEGIS-based cipher suites, the mask is generated using the AEGIS Stream and ZeroPad functions defined in [I-D.irtf-cfrg-aegis-aead] with:

  • a 128-bit tag length

  • sn_key, as defined in [RFC9147], Section 4.2.3

  • ciphertext[0..16]: the first 16 bytes of the DTLS ciphertext

  • nonce_len: the AEGIS nonce length, either 16 or 32, depending on the chosen AEAD algorithm.

A 48-bit mask is computed as follows:

mask = Stream(5, sn_key, ZeroPad(ciphertext[0..16], nonce_len))

5. QUIC Header Protection

In QUIC, specific segments of the QUIC packet headers undergo encryption in accordance with the specifications outlined in [RFC9001], Section 5.4.

For AEGIS-based cipher suites, the mask is generated following the same procedure as in DTLS 1.3, utilizing:

  • a 128-bit tag length

  • hp_key, as defined in [RFC9001], Section 5.4

  • ciphertext[0..16]: the first 16 bytes of the ciphertext

  • nonce_len: the AEGIS nonce length, either 16 or 32, depending on the selected AEAD algorithm.

A 48-bit mask is computed as follows:

mask = Stream(5, hp_key, ZeroPad(ciphertext[0..16], nonce_len))

6. Operational Considerations

On devices lacking hardware AES acceleration or protection against side-channel attacks, cipher suites dependent on the AES round function SHOULD NOT be prioritized. This recommendation encompasses the cipher suites outlined in this document

On devices equipped with secure hardware AES acceleration, implementations SHOULD prioritize AEGIS-based cipher suites over AES-GCM ones of equivalent security levels.

7. Implementation Status

This note is to be removed before publishing as an RFC.

A list of early implementations can be found at https://github.com/jedisct1/draft-denis-tls-aead,

8. Security Considerations

A key update MUST be performed prior to encrypting 248 records with the same key. The prescribed mechanism is documented in [RFC8446], Section 4.6.3.

9. IANA Considerations

IANA is requested to register the following identifiers in the TLS Cipher Suite Registry:

Table 2: Requested IANA identifiers
Description DTLS-OK Recommended
TLS_AEGIS_128L_SHA256 Y N
TLS_AEGIS_128X2_SHA512 Y N
TLS_AEGIS_256_SHA256 Y N
TLS_AEGIS_256X2_SHA512 Y N

10. References

10.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9000]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9001]
Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure QUIC", RFC 9001, DOI 10.17487/RFC9001, , <https://www.rfc-editor.org/rfc/rfc9001>.
[RFC9147]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", RFC 9147, DOI 10.17487/RFC9147, , <https://www.rfc-editor.org/rfc/rfc9147>.

10.2. Informative References

[I-D.irtf-cfrg-aegis-aead]
Denis, F. and S. Lucas, "The AEGIS Family of Authenticated Encryption Algorithms", Work in Progress, Internet-Draft, draft-irtf-cfrg-aegis-aead-09, , <https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-aegis-aead-09>.
[M23]
Mattsson, J. P., "Hidden Stream Ciphers and TMTO Attacks on TLS 1.3, DTLS 1.3, QUIC, and Signal", Cryptology ePrint Archive, Paper 2023/913, DOI 10.1007/978-981-99-7563-1_12, , <https://eprint.iacr.org/2023/913.pdf>.

Appendix A. Examples

A.1. TLS 1.3 Handshake

A.1.1. With TLS_AEGIS_128L_SHA256

shared_key:           cbb2b72da2bc70eb85fae05a8f6bc929
                      6f3e2f9693e5972a7b2a3da608e5eda2

hello_hash:           b77594edb8abd3acc4db7f5ead5869e1
                      96fff7d0fb1beb2bffbaac850bf479d8

early_secret:         33ad0a1c607ec03b09e6cd9893680ce2
                      10adf300aa1f2660e1b22e10f170f92a

handshake_secret:     15614a4e6a6c590f16e9760dc20002a1
                      2af27d6ceda73c66a9477de4b690639f

client_secret:        6e60b228fdd7c8b08ac50e5018fa79ec
                      3f8cd2ee023386111b0d7a2027e5c1b8

client_handshake_key: 2474bdcd8e8c8dff18af9e169e4470ea

client_handshake_iv:  42fe48bd086cc5ddaf43be4500d0c7f2

server_handshake_key: e0d7ea14104a89cfdf253e1f0e0302b0

server_handshake_iv:  cc421814028367299508e120a7cb3ad2

A.1.2. With TLS_AEGIS_256_SHA512

shared_key:           724d41a7ccadc6435d4305dd6756bd01
                      5e26dd0544a19733a2c08430f128b218

hello_hash:           1a8fd72e2630e12817d768bae1248367
                      30c07141c4ab4cc3423d7f16c3c1a84b
                      91d4c4194453dbc85fca8738b4e9ea3c
                      783bb6d99f579fd6c2f599c69c1c79e1

early_secret:         fd4a40cb6252b3c08d9b88d5bde85339
                      03caa51a1dba1c79ce18eea0365d35d0
                      71e597a2b95214821100e812f7b79828
                      498f164707cd63c6f7464973cfa22046

handshake_secret:     55ef8c23352da78bf1daa4626445c883
                      b842bec578769fe9ae6fbf6de5c28953
                      02ec3cbb22b3a94ea1d047ab08cce64e
                      1079f3dbc9bf08152dc3b0bcd74ac977

client_secret:        728f1edab4426f4dac3f03180b0bc537
                      a0d555514b439ea4f4cccb5910834807
                      408d29b9c79dcbff8e3a3fb8bf220907
                      d96ce595eee7ffaf9f9735e4f6da1e60

client_handshake_key: 08a37693b14937177d75149422944c34
                      9019de948f6922c2c516d941c0bdafe4

client_handshake_iv:  e0a2155fedcb592a29588bdcf06334f0
                      4dc6b5c40e659051e62071cb87f8be2c

server_handshake_key: 366e1ebfb124508aa69137ccef542756
                      c0a748525c5bdc16acd79c66856e7c82

server_handshake_iv:  8f883c1bb0eae38960efdb717f6b19cf
                      c929d565ad596f1f4b3daab498a7fc29

A.2. TLS 1.3 Nonces for Record Encryption

A.2.1. With TLS_AEGIS_128L_SHA256

handshake_iv:         cc421814028367299508e120a7cb3ad2

sequence_number:      0102030405

nonce:                cc421814028367299508e121a5c83ed7

A.2.2. With TLS_AEGIS_128L_SHA512

handshake_iv:         724d41a7ccadc6435d4305dd6756bd01
                      5e26dd0544a19733a2c08430f128b218

sequence_number:      0102030405

nonce:                724d41a7ccadc6435d4305dd6756bd01
                      5e26dd0544a19733a2c08431f32bb61d

A.3. DTLS 1.3 and QUIC Header Protection Mask

A.3.1. With TLS_AEGIS_128L_SHA256

key:                  000102030405060708090a0b0c0d0e0f

ciphertext[0..16]:    101112131415161718191a1b1c1d1e1f

nonce_len:            16

mask:                 60ede1c811

A.3.2. With TLS_AEGIS_128X2_SHA256

key:                  000102030405060708090a0b0c0d0e0f

ciphertext[0..16]:    101112131415161718191a1b1c1d1e1f

nonce_len:            16

mask:                 6bf2292472

A.3.3. With TLS_AEGIS_256_SHA512

key:                  000102030405060708090a0b0c0d0e0f
                      101112131415161718191a1b1c1d1e1f

ciphertext[0..16]:    202122232425262728292a2b2c2d2e2f

nonce_len:            32

mask:                 6e3a2ce297

A.3.4. With TLS_AEGIS_256X2_SHA512

key:                  000102030405060708090a0b0c0d0e0f
                      101112131415161718191a1b1c1d1e1f

ciphertext[0..16]:    202122232425262728292a2b2c2d2e2f

nonce_len:            32

mask:                 7a515cfb0c

Acknowledgments

We would like to thank John Preuß Mattsson for suggesting how AEGIS should be used in the context of DTLS and QUIC.

Authors' Addresses

Frank Denis
Fastly Inc.
Samuel Lucas
Individual Contributor