Use of GOST 2012 Signature Algorithms in DNSKEY and RRSIG Resource Records for DNSSEC

Introduction The Domain Name System (DNS) is the global hierarchically distributed database for Internet Naming. The DNS has been extended to use cryptographic keys and digital signatures for the verification of the authenticity and integrity of its data. RFC 4033 , RFC 4034 , and RFC 4035 describe these DNS Security Extensions, called DNSSEC. RFC 4034 describes how to store DNSKEY and RRSIG resource records, and specifies a list of cryptographic algorithms to use. This document extends that list with the signature and hash algorithms GOST R 34.10-2012 () and GOST R 34.11-2012 (), and specifies how to store DNSKEY data and how to produce RRSIG resource records with these algorithms. Algorithms GOsudarstvennyy STandart(GOST) R 34.10-2012 and GOST R 34.11-2012 are Russian national standards. Their cryptographic properties haven't been independently verified. Familiarity with DNSSEC and with GOST signature and hash algorithms is assumed in this document.

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 when, and only when, they appear in all capitals, as shown here.

DNSKEY Resource Records The format of the DNSKEY RR can be found in RFC 4034 . GOST R 34.10-2012 public keys are stored with the algorithm number TBA1. According to RFC 7091 , a GOST R 34.10-2012 public key is a point on the elliptic curve Q = (x,y). The wire representation of a public key MUST contain 64 octets, where the first 32 octets contain the little-endian representation of x and the second 32 octets contain the little-endian representation of y. As RFC 6986 and RFC 7091 allows 2 variants of length of the output hash and signature and many variants of parameters of the digital signature, for the purpose of this document we use 256-bit variant of the digital signature algorithm, corresponding 256-bit variant of the digest algorithm. We select the parameters for the digital signature algorithm to be id-tc26-gost-3410-2012-256-paramSetA as specified in RFC 7836 .

Using a Public Key with Existing Cryptographic Libraries At the time of this writing, existing GOST-aware cryptographic libraries are capable of reading GOST R 34.10-2012 public keys via a generic X.509 API if the key is encoded according to RFC 9215 , Section 4. To make this encoding from the wire format of a GOST R 34.10-2012 public key with the parameters used in this document, prepend the 64 octets of key data with the following 30-byte sequence: These bytes provide the following ASN.1 structure suitable for parsing by cryptographic toolkits: The OIDs in the structure above represent GOST R 34.10-2012 public key with 256 bits private key length algorithm and Parameter set A. The structure itself represents SubjectPublicKeyInfo field of an X.509 certificate as defined in RFC 5280 , Section 4.1.

GOST DNSKEY RR Example Given a private key with the following value: The following DNSKEY RR stores a DNS zone key for example: The private key here is presented in PrivateKeyInfo ASN.1 structure, as described in RFC5208 , Section 5. Public key can be calculated from the private key using algorithm described in RFC 7091 . [RFC Editor note: Note: Algorithm numbers 23 and 5 are used as an example in this document, as actual numbers have not yet been assigned. If the assigned values will differ, the example keys and signatures will have to be recalculated before the official publication of the RFC.]

RRSIG Resource Records The value of the signature field in the RRSIG RR follows RFC 7091 and is calculated as follows. The values for the RDATA fields that precede the signature data are specified in RFC 4034 . where "data" is the wire format data of the resource record set that is signed, as specified in RFC 4034 . The signature is calculated from the hash according to the GOST R 34.10-2012 standard, and its wire format is compatible with RFC 7091 .

RRSIG RR Example Consider a given RRset consisting of one MX RR to be signed with the private key described in Section 2.2 of this document: Setting the inception date to 2022-10-06 12:32:30 UTC and the expiration date to 2022-11-03 12:32:30 UTC, the following signature RR will be valid: The GOST R 34.10-2012 signature algorithm uses random (pseudorandom) integer k as described in Section 6.1 of RFC 7091 . The following value for k was used to produce the signature example. This value for k MUST NOT be used when computing GOST R 34.10-2012 signatures. It is provided only so the above signature example can be reproduced. The actual signature value will differ between signature calculations.

DS Resource Records The GOST R 34.11-2012 digest algorithm is denoted in DS RRs by the digest type TBA2. The wire format of a digest value is compatible with RFC 6986 .

DS RR Example For Key Signing Key (KSK): The DS RR will be:

Operational Considerations

Key Sizes The key size of GOST R 34.10-2012 public keys conforming to this specification MUST be 512 bits according to RFC 7091 .

Signature Sizes The size of a GOST R 34.10-2012 signature conforming to this specification MUST be 512 bits according to RFC 7091 .

Digest Sizes The size of a GOST R 34.11-2012 digest conforming to this specification MUST be 256 bits according to RFC 6986 .

Implementation Considerations The support of this cryptographic suite in DNSSEC-aware systems is OPTIONAL. According to RFC6840 , Section 5.2 systems that do not support these algorithms MUST ignore the RRSIG, DNSKEY and DS resource records associated with the GOST R 34.10-2012 digital signature algorithm. [(To be removed in RFC). To check the correctness of the implementation, authors recommend using OpenSSL 1.1.1 or 3.0.x series, a fork of ldns available at https://github.com/beldmit/ldns/tree/gost2012, and a reference implementation of GOST crypto algorithms available at https://github.com/gost-engine/engine.]

IANA Considerations This document updates the IANA registry "DNS Security Algorithm Numbers". The following entries have been added to the registry: This document updates the IANA registry "Digest Algorithms" in the "Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms" registry group by adding an entry for the GOST R 34.11-2012 algorithm: [RFC editor note: For the purpose of example computations, the following values were used: TBA1 = 23, TBA2 = 5. If the assigned values will differ, the example keys and signatures will have to be recalculated before the official publication of the RFC.]

Security Considerations It is recommended to use a dual KSK algorithm signed zone until GOST-aware DNSSEC software become more widespread, unless GOST-only cryptography is required. Otherwise, GOST-signed zones may be considered unsigned by the DNSSEC software currently in use. Currently, the cryptographic resistance of the GOST R 34.10-2012 digital signature algorithm is estimated as 2**128 operations of multiple elliptic curve point computations on prime modulus of order 2**256. Currently, the cryptographic collision resistance of the GOST R 34.11-2012 hash algorithm is estimated as 2**128 operations of computations of a step hash function.

Acknowledgments This document is a minor extension to RFC 4034 . Also, we tried to follow the documents RFC 3110 , RFC 4509 , and RFC 5933 for consistency. The authors of and contributors to these documents are gratefully acknowledged for their hard work. The following people provided additional feedback, text, and valuable assistance: Alexander Venedyukhin, Michael StJohns, Valery Smyslov, Tim Wicinski, Stephane Bortzmeyer.