Using GOST Cryptographic Algorithms in the Internet Key Exchange Protocol Version 2 (IKEv2)

The Internet Key Exchange protocol version 2 (IKEv2) defined in is an important part of the IP Security (IPsec) architecture. It is used for the authenticated key exchange and for the negotiation of various protocol parameters and features. This document defines a number of transforms for IKEv2, based on Russian cryptographic standard algorithms (often reffered to as "GOST" algorithms) for hash function, digital signature and key exchange method. These definitions are based on the recommendations established by the Standardisation Technical Committee "Cryptographic information protection", which describe how Russian cryptographic standard algorithms are used in IKEv2. Along with the transforms defined in , the transforms defined in this specification allow using GOST cryptographic algorithms in IPsec protocols. This specification was developed to facilitate implementations that wish to support the GOST algorithms. This document does not imply IETF endorsement of the cryptographic algorithms 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 when, and only when, they appear in all capitals, as shown here.

Russian cryptographic standard (GOST) algorithms are a set of cryptographic algorithms of different types - ciphers, hash functions, digital signatures etc. In particular, Russian cryptographic standard defines block ciphers "Kuznyechik" (also defined in ) and "Magma" (also defined in ). Cryptographic standard defines elliptic curve digital signature algorithm (also defined in ), while defines two cryptographic hash functions "Streebog", with different output length (also defined in ). The parameters for the elliptic curves used in GOST signature and key exchange algorithms are defined in .

defines two transforms of type 1 (Encryption Algorithm Transform IDs) based on GOST block ciphers that can be used for IKE SA protection: ENCR_KUZNYECHIK_MGM_KTREE (32) based on "Kuznyechik" block cipher and ENCR_MAGMA_MGM_KTREE (33) based on "Magma" block cipher. Since these transforms use ciphers in Multilinear Galois Mode (MGM), which provides Authenticated Encryption with Associated Data (AEAD) and thus provide both encryption and authentication, there is no need for new transform type 3 (Integrity Algorithm Transform IDs) for use in IKEv2, because integrity transforms cannot be used with encryption transforms providing AEAD (see Section 3.3 of ).

This specification defines a new transform of type 2 (Pseudorandom Function Transform IDs) - PRF_HMAC_STREEBOG_512 (9). This transform uses PRF HMAC_GOSTR3411_2012_512 defined in Section 4.1.2 of . The PRF uses GOST R 34.11-2012 ("Streebog") hash-function with 512-bit output defined in with HMAC construction. The PRF has a 512-bit block size and a 512-bit output length.

This specification defines two new transforms of type 4 (Diffie-Hellman Group Transform IDs): GOST3410_2012_256 (33) and GOST3410_2012_512 (34). These transforms uses Elliptic Curve Diffie-Hellman (ECDH) key exchange algorithm over Twisted Edwards curves. The parameters for these curves are defined in Section A.2 of . In particular, transform GOST3410_2012_256 uses id-tc26-gost-3410-2012-256-paramSetA parameter set and GOST3410_2012_512 uses id-tc26-gost-3410-2012-512-paramSetC parameter set (both defined in ). Shared secret is computed as follows. The initiator randomly selects its private key d_i from {1,..,q - 1}, where q is the group order and is a parameter of the selected curve. Then a public key Q_i is computed as a point on the curve: Q_i = d_i * G, where G is the generator for the selected curve, and then is sent to the responder. The responder makes the same calculations to get d_r and Q_r and sends Q_r to the initiator. After peers exchange Q_i and Q_R both sides can compute a point on the curve S = ((m / q) * d_i) * Q_r = ((m / q) * d_r) * Q_i, where m is the subgroup order and is a parameter of the selected curve. The shared secret K is an x coordinate of S in a little-endian representation. The size of K is determined by the size of used curve and is either 256 or 512 bit. When GOST public key is transmitted in the KE payload, it MUST be represented as x coordinate immediately followed by y coordinate, each in a little-endian representation. The size of each coordinate is determined by the size of the used curve and is either 256 or 512 bits, so that the size of the Key Exchange Data field in the KE payload is either 64 or 128 octets.

Upon receiving peer's public key implementations MUST check that the key is actually a point on the curve, otherwise the exchange fails. Implementations MUST check that the calculated public value S is not an identity element of the curve, in which case the exchange fails. The INVALID_SYNTAX notification MAY be sent in these cases.

GOST digital signatures algorithm GOST R 34.10-2012 is defined in . There are two variants of GOST signature algorithm - one over 256-bit elliptic curve and the other over 512-bit key elliptic curve. When GOST digital signature is used in IKEv2 for authentication purposes, an Authentication Method "Digital Signature" (14) MUST be specified in the AUTH payload. The AlgorithmIdentifier ASN.1 objects for GOST digital signature algorithm are defined in . The signature value, as defined in , consists of two integers r and s. The size of each integer is either 256 bit or 512 bit depending on the used elliptic curve. The content of the Signature Value field in the AUTH payload MUST consist of s immediately followed by r, each in a big-endian representation, so that the size of the field is either 64 or 128 octets.

GOST digital signatures algorithm uses GOST hash functions GOST R 34.11-2012 ("Streebog") defined in . There are two "Streebog" hash functions - one with 256-bit output length and the other with 512-bit output length. This specification defines two new values for IKEv2 Hash Algorithms registry: STREEBOG_256 (6) for GOST hash function with 256-bit output length and STREEBOG_512 (7) for the 512-bit length output. These values MUST be included in the SIGNATURE_HASH_ALGORITHMS notify if a corresponding GOST digital signature algorithm is supported by the sender.

This section lists GOST signature algorithm ASN.1 AlgorithmIdentifier objects in binary form. This objects are defined in and are provided here for convenience.

id-tc26-signwithdigest-gost3410-12-256 OBJECT IDENTIFIER ::= { iso(1) member-body(2) ru(643) rosstandart(7) tc26(1) algorithms(1) signwithdigest(3) gost3410-12-256(2) } Parameters are absent.

id-tc26-signwithdigest-gost3410-12-512 OBJECT IDENTIFIER ::= { iso(1) member-body(2) ru(643) rosstandart(7) tc26(1) algorithms(1) signwithdigest(3) gost3410-12-512(3) } Parameters are absent.

The security considerations of apply accordingly. The security of GOST elliptic curves is discussed in . The security of "Streebog" hash function is discussed in . A second preimage attack on "Streebog" is described in if message size exceeds 2^259 blocks. This attack is not relevant to how "Streebog" is used in IKEv2.

IANA has assigned one Transform ID in the "Transform Type 2 - Pseudorandom Function Transform IDs" registry (where RFCXXXX is this document):

IANA has assigned two Transform IDs in the "Transform Type 4 - Diffie-Hellman Group Transform IDs" registry (where RFCXXXX is this document):

IANA has assigned two values in the "IKEv2 Hash Algorithms" registry (where RFCXXXX is this document):