Network Working Group C. Wynn Internet-Draft NSA Intended status: Standards Track S. Fluhrer Expires: 23 April 2027 Cisco Systems R. Guthrie 20 October 2026 Using AES-GCM-SIV in the Internet Protocol Version 2 (IKEv2) and Encapsulating Security Payload (ESP) Protocols draft-guthrie-ipsecme-aes-gcm-siv-02 Abstract This document specifies the use of AES-GCM-SIV in the Internet Key Exchange Protocol version 2 (IKEv2) and the Encapsulating Security Payload (ESP) protocols. This document also adds AES-GCM-SIV to the IANA IKEv2 registry for "Transform Type 1 - Encryption Algorithm Transform IDs." AES-GCM-SIV is a nonce misuse-resistant authenticated encryption with associated data (AEAD) algorithm based on AES-GCM. 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 23 April 2027. Copyright Notice Copyright (c) 2026 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 Wynn, et al. Expires 23 April 2027 [Page 1] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 2. AES-GCM-SIV Overview . . . . . . . . . . . . . . . . . . . . 3 3. AES-GCM-SIV in IKEv2 . . . . . . . . . . . . . . . . . . . . 4 3.1. IKEv2 Encrypted Payload Data . . . . . . . . . . . . . . 4 3.2. IKEv2 Keying Material . . . . . . . . . . . . . . . . . . 5 3.3. Associated Data Construction . . . . . . . . . . . . . . 5 4. AES-GCM-SIV in ESP . . . . . . . . . . . . . . . . . . . . . 5 4.1. ESP Payload Data . . . . . . . . . . . . . . . . . . . . 5 4.2. ESP Integrity Check Value (ICV) . . . . . . . . . . . . . 6 4.3. ESP Keying Material . . . . . . . . . . . . . . . . . . . 6 4.4. Additional Authenticated Data Construction . . . . . . . 6 5. IKE Conventions . . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Operational Considerations . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction An authenticated encryption with associated data (AEAD) algorithm combines encryption and integrity into a single operation and returns ciphertext and an integrity check value (ICV) (also called an authentication tag) over the plaintext or ciphertext and the associated/additional data. A commonly used AEAD algorithm is AES- GCM (the Advanced Encryption Standard (AES) block cipher used in Galois/Counter mode)(GCM) [SP-800-38D], which offers certain performance advantages over other AES-based options that also provide both confidentiality and message authentication. However, AES-GCM fails catastrophically when two different plaintext messages are encrypted under the same key and nonce: confidentiality is compromised, and the long-term authentication key is exposed. While specifications of AES-GCM require a unique nonce per message, this can be difficult to guarantee in practice due to poor random number generation or failure to keep track of state, either of which can result in a nonce repeating. Because of this, [RFC4106] disallows use of AES-GCM in ESP with statically configured keys and requires Wynn, et al. Expires 23 April 2027 [Page 2] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 use of IKE or other automated key management system. As a remedy, this document specifies the use of AES-GCM-SIV ([RFC8452]) in ESP as well as IKE. AES-GCM-SIV, being a nonce- misuse-resistant AEAD, prevents the failure noted above. In particular, when two messages are encrypted using the same AES-GCM- SIV nonce and key, the ciphertext and ICV/authentication tag associated with each message can only reveal whether the two messages are equal. This document does not encourage repeated use of a nonce. Instead, it aims to enhance security, requiring that nonces be randomly generated. This document also adds AES-GCM-SIV to the IANA IKEv2 registry for "Transform Type 1 - Encryption Algorithm Transform IDs." 1.1. Conventions Used in This Document 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. 2. AES-GCM-SIV Overview Though AES-GCM-SIV is based on AES-GCM, there are several key differences between the two algorithms; these differences prevent the specifications for AES-GCM in IKEv2 and ESP from directly supporting AES-GCM-SIV. This section gives an overview of these differences and highlights how these differences manifest in the IKEv2 and ESP protocols. The typical nonce construction for AES-GCM in IKEv2 and ESP is called "partially implicit" (Section 4 of [RFC5282]). It consists of a four-octet salt that is part of the IKEv2 keying material shared between parties (the implicit portion, which is not transmitted), followed by the eight-octet Initialization Vector (IV) included in the Encrypted payload (this is the explicit portion; hence "partially" implicit). The IV must be chosen in such a way that is only used once. Note in particular that the IV is defined as a component of this partially implicit nonce. In contrast, all of the AEAD inputs to AES-GCM-SIV, the 12-octet nonce, the key-generating key, and the associated data, are used to derive the synthetic IV (SIV). Each AES-GCM-SIV nonce is random, and does not contain a salt. Specifically, there is no need for a salt because AES-GCM-SIV with random nonces is not vulnerable to multitarget attacks. Wynn, et al. Expires 23 April 2027 [Page 3] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 Because of these structural differences, IKEv2 and ESP fields specified for AES-GCM nonce and IV cannot be used for the AES-GCM-SIV nonce and SIV without modification. While the AES-GCM ciphertext (as described in [RFC5282]) and AES-GCM- SIV ciphertext both include an authentication tag, the authentication tag for AES-GCM can be 8, 12, or 16 octets. In contrast, the authentication tag for AES-GCM-SIV MUST be 16 octets. This is because the AES-GCM-SIV authentication tag is needed to decrypt the ciphertext, so it must be transmitted in full (i.e., not truncated). 3. AES-GCM-SIV in IKEv2 The Internet Key Exchange version 2 [RFC7296] protocol is a component of IPsec [RFC4301] that establishes a Security Association (SA) with a shared session secret from which cryptographic keys are derived. This SA can facilitate the establishment of further SAs for Encapsulating Security Payload (ESP) [RFC4303] or Authentication Header [RFC4302], and the cryptographic keys are used to protect the traffic carried by each SA. [RFC7296] specifies generally how to negotiate and use cryptographic algorithms that provide properties such as encryption and integrity of the IKE SA. [RFC5282] specifies how to use AES-GCM as a Transform Type 1 algorithm to provide both encryption and integrity to the IKEv2 SA. This section specifies how to use AES-GCM-SIV for the same purpose and uses portions of [RFC5282] as a baseline. 3.1. IKEv2 Encrypted Payload Data The Encrypted payload (Section 3.14 of [RFC7296]) contains all the payloads of a given IKEv2 message in encrypted form. Section 3 (or Figure 1) of [RFC5282] updates the format of the Encrypted payload as depicted in Figure 21 of [RFC7296] in the case that one of the authenticated encryption algorithms AES-GCM or AES-CCM are used. This updated format contains two fields: an 8-octet Initialization Vector field followed by a variable-length Ciphertext field. The Encrypted payload format for AES-GCM-SIV aligns with the modified format from [RFC5282] with one exception: the Initialization Vector field is now 12-octets in length, which is the value of the AES-GCM- SIV nonce. Then, the Encrypted payload has the following structure: * Initialization Vector: a twelve-octet randomly-generated AES-GCM- SIV nonce, followed by Wynn, et al. Expires 23 April 2027 [Page 4] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 * Ciphertext: a variable-length ciphertext, which does include the 16-octet tag The Nonce field contains a randomly-generated 96-bit (12-octet) value. The Ciphertext field contains the ciphertext as specified by [RFC8452]. The ciphertext as specified by [RFC8452] contains a 16-octet authentication tag, making it 16 octets longer than the corresponding plaintext. The presence of the authentication tag in the Ciphertext field makes it so that a separate Integrity Check Value field in the Encrypted payload is not needed. 3.2. IKEv2 Keying Material Parties in IKEv2 generate a quantity called SKEYSEED from which all keys used in the IKEv2 SA are derived (Section 2.14 of [RFC7296]). AES-GCM-SIV uses one of these keys, SK_e[i/r], as a key-generating key from which to derive further keying material. SK_e[i/r] is either 128 or 256 bits, depending on whether AES-128 or AES-256 is in use. In particular, the key-generating key and the 96-bit nonce are used to derive a 128-bit message-authentication key and either a 128-bit or 256-bit (consistent with the length of the key-generating key, for use in AES-128 or AES-256 respectively) message-encryption key (see Section 4 of [RFC8452]). The authentication keys SK_a[i/r] from SKEYSEED are treated as having a length of zero octets and are not used, consistent with the treatment of SK_a[i/r] for AES-GCM by Section 7.1 of [RFC5282]. 3.3. Associated Data Construction The construction of the associated data for AES-GCM-SIV (referred to as "additional data" by [RFC8452]) is as specified for AES-GCM in Section 5.1 of [RFC5282]. 4. AES-GCM-SIV in ESP 4.1. ESP Payload Data ESP packets contain a variable-length field, called Payload Data [RFC4303]. The format of the Payload Data field is dependent upon the encryption algorithm being used. In the case of AES-GCM-SIV, the ESP Payload Data field is composed of two subfields: * IV: a twelve-octet AES-GCM-SIV nonce, followed by Wynn, et al. Expires 23 April 2027 [Page 5] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 * Ciphertext: a variable-length ciphertext. The IV field contains a randomly-generated 96-bit (12-octet) value, and is the value presented to the AES-GCM-SIV implementation as the nonce. The Ciphertext field contains the encryption of the padded plaintext, which is the same length as the padded plaintext. Note that, in this description, this does not include the 16 octet tag, which is the ICV. 4.2. ESP Integrity Check Value (ICV) The ESP Packet Format depicted in Figure 1 of [RFC4303] includes a variable-length Integrity Check Value (ICV) field. This field contains the AES-GCM-SIV 16-octet authentication tag, as generated by the encryption algorithm. Note that this distinction between ciphertext and ICV differs from that specified by [RFC8452], which considers both to be part of the "ciphertext". Because the two fields are adjacent in both cases, this is just a terminology difference, rather than an actual protocol difference. 4.3. ESP Keying Material The transform keys are extracted from the KEYMAT as defined in Section 2.17 of [RFC7296]. When AES-GCM-SIV with AES-128 is used, 16 octets are extracted; when AES-GCM-SIV with AES-256 is used, 32 octets are extracted. 4.4. Additional Authenticated Data Construction The construction of the Additional Authenticated Data (AAD) for AES- GCM-SIV is as specified for AES-GCM in Section 5 of [RFC4106]. 5. IKE Conventions Because AES-GCM-SIV supports two key lengths (128 and 256 bits), the Key Length attribute MUST be specified in the IKE Phase 2 exchange [RFC7296]. The Key Length attribute MUST have a value of 128 or 256. 6. Security Considerations This document inherits the security considerations of [RFC8452]. Wynn, et al. Expires 23 April 2027 [Page 6] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 7. Operational Considerations Implementers of IPsec may assess the benefits and drawbacks of using AES-GCM-SIV in a given deployment scenario versus another AEAD algorithm. While AES-GCM-SIV decryption speed is comparable to that of AES-GCM, its encryption runs at about two thirds the speed of AES- GCM encryption. Because of this, it is not prudent to view AES-GCM- SIV as a blanket replacement for AES-GCM. [RFC8452] recommends that AES-GCM-SIV be used in any scenario where nonce uniqueness cannot be guaranteed, such as when there is no stateful counter, or when multiple encryptors use the same key. 8. IANA Considerations This document adds the following algorithm to the IANA "Transform Type 1 - Encryption Algorithm Transform IDs" registry for use in both IKEv2 and ESP: +--------------------------------+ | Number | Name | +--------------------------------| | TBD | ENCR_AES_GCM_SIV | +--------------------------------+ 9. References 9.1. 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, . [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)", RFC 4106, DOI 10.17487/RFC4106, June 2005, . [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, . [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005, . Wynn, et al. Expires 23 April 2027 [Page 7] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption Algorithms with the Encrypted Payload of the Internet Key Exchange version 2 (IKEv2) Protocol", RFC 5282, DOI 10.17487/RFC5282, August 2008, . [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8452] Gueron, S., Langley, A., and Y. Lindell, "AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption", RFC 8452, DOI 10.17487/RFC8452, April 2019, . [SP-800-38D] Dworkin, M., "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", NIST SP- 800-38D, November 2007, . 9.2. Informative References [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005, . Appendix A. Acknowledgements The authors would like to thank Nicholas Gajcowski for his contributions to this draft. Authors' Addresses Casey Wynn National Security Agency Email: cwwynn@uwe.nsa.gov Scott Fluhrer Cisco Systems Email: sfluhrer@cisco.com Wynn, et al. Expires 23 April 2027 [Page 8] Internet-Draft Using AES-GCM-SIV in IKEv2 and ESP October 2026 Rebecca Guthrie Email: rguthrie13245@proton.me Wynn, et al. Expires 23 April 2027 [Page 9]