Internet-Draft SLH-DSA for X.509 July 2024
Bashiri, et al. Expires 6 January 2025 [Page]
Workgroup:
LAMPS - Limited Additional Mechanisms for PKIX and SMIME
Internet-Draft:
draft-ietf-lamps-x509-slhdsa-01
Published:
Intended Status:
Standards Track
Expires:
Authors:
K. Bashiri
BSI
S. Fluhrer
Cisco Systems
S. Gazdag
genua GmbH
D. Van Geest
CryptoNext Security
S. Kousidis
BSI

Internet X.509 Public Key Infrastructure: Algorithm Identifiers for SLH-DSA

Abstract

Digital signatures are used within X.509 Public Key Infrastructure such as X.509 certificates, Certificate Revocation Lists (CRLs), and to sign messages. This document describes the conventions for using the Stateless Hash-Based Digital Signature Standard (SLH-DSA) in X.509 Public Key Infrastructure. The conventions for the associated signatures, subject public keys, and private key are also described.

[EDNOTE: This draft is not expected to be finalized before the NIST PQC Project has standardized FIPS 205 Stateless Hash-Based Digital Signature Standard. The current FIPS draft was published August 24, 2023 for public review. Final versions are expected by April 2024. This specification will use object identifiers for the new algorithms that are assigned by NIST, and will use placeholders until these are released.]

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-ietf-lamps-x509-slhdsa/.

Discussion of this document takes place on the LAMPS Working Group mailing list (mailto:spasm@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/spasm/. Subscribe at https://www.ietf.org/mailman/listinfo/spasm/.

Source for this draft and an issue tracker can be found at https://github.com/x509-hbs/draft-x509-slhdsa.

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 6 January 2025.

▲

Table of Contents

1. Introduction

Stateless Hash-Based Digital Signatures (SLH-DSA) is a quantum-resistant digital signature scheme standardized in [FIPS205] [EDNOTE: [FIPS205-ipd] until officially published] by the US National Institute of Standards and Technology (NIST) PQC project [NIST-PQC]. This document specifies the use of the SLH-DSA algorithm in Public Key Infrastructure X.509 (PKIX) certificates and Certificate Revocation Lists (CRLs).

SLH-DSA offers three security levels. The parameters for each of the security levels were chosen to provide 128 bits of security, 192 bits of security, and 256 bits of security. There are small (s) or fast (f) version of the algorithm, and the option to use SHA-256 [FIPS180] or SHAKE256 [FIPS202]. The fast versions are optimized for key generation and signing speed, they are actually slower at verification than the small parameter sets. For example, id-alg-slh-dsa-shake-256s represents the 256-bit security level, the small version of the algorithm, and the use of SHAKE256.

Separate algorithm identifiers have been assigned for SLH-DSA at each of these security levels, fast vs small, and SHA-256 vs SHAKE256.

This specification includes conventions for the encoding of SLH-DSA digital signatures and public keys in the X.509 Public Key Infrastructure.

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. Algorithm Identifiers

This specification uses placeholders for object identifiers until the identifiers for the new algorithms are assigned by NIST.

The AlgorithmIdentifier type, which is included herein for convenience, is defined as follows:

    AlgorithmIdentifier  ::=  SEQUENCE  {
        algorithm   OBJECT IDENTIFIER,
        parameters  ANY DEFINED BY algorithm OPTIONAL
    }

    |  NOTE: The above syntax is from [RFC5280] and matches the
    |  version used therein, i.e., the 1988 ASN.1 syntax.  See
    |  [RFC5912] for ASN.1 copmatible with the 2015 ASN.1 syntax.

The fields in AlgorithmIdentifier have the following meanings:

The OIDs are:

   nistAlgorithms OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
     country(16) us(840) organization(1) gov(101) csor(3) 4 }

   sigAlgs OBJECT IDENTIFIER ::= { nistAlgorithms 3 }

   id-alg-slh-dsa-sha2-128s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-sha2-128f OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-sha2-192s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-sha2-192f OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-sha2-256s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-sha2-256f OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-128s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-128f OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-192s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-192f OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-256s OBJECT IDENTIFIER ::= { sigAlgs TBD }

   id-alg-slh-dsa-shake-256f OBJECT IDENTIFIER ::= { sigAlgs TBD }

The contents of the parameters component for each algorithm are absent.

4. SLH-DSA Signatures in PKIX

SLH-DSA is a digital signature scheme built upon hash functions. The security of SLH-DSA relies on the presumed difficulty of finding preimages for hash functions as well as several related properties of the same hash functions.

Signatures are used in a number of different ASN.1 structures. As shown in the ASN.1 representation from [RFC5280] below, in an X.509 certificate, a signature is encoded with an algorithm identifier in the signatureAlgorithm attribute and a signatureValue attribute that contains the actual signature.

    Certificate  ::=  SEQUENCE  {
        tbsCertificate       TBSCertificate,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

Signatures are also used in the CRL list ASN.1 representation from [RFC5280] below. In a X.509 CRL, a signature is encoded with an algorithm identifier in the signatureAlgorithm attribute and a signatureValue attribute that contains the actual signature.

    CertificateList  ::=  SEQUENCE  {
        tbsCertificate       TBSCertList,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

The identifiers defined in Section 3 can be used as the AlgorithmIdentifier in the signatureAlgorithm field in the sequence Certificate/CertificateList and the signature field in the sequence TBSCertificate/TBSCertList in certificates CRLs, respectively, [RFC5280]. The parameters of these signature algorithms are absent, as explained in Section 3.

The signatureValue field contains the corresponding SLH-DSA signature computed upon the ASN.1 DER encoded tbsCertificate [RFC5280].

Conforming Certification Authority (CA) implementations MUST specify the algorithms explicitly by using the OIDs specified in Section 3 when encoding SLH-DSA signatures in certificates and CRLs. Conforming client implementations that process certificates and CRLs using SLH-DSA MUST recognize the corresponding OIDs. Encoding rules for SLH-DSA signature values are specified Section 3.

When any of the id-alg-slh-dsa-* identifiers appear in the algorithm field as an AlgorithmIdentifier, the encoding MUST omit the parameters field. That is, the AlgorithmIdentifier SHALL be a SEQUENCE of one component, the id-alg-slh-dsa-* OID.

5. SLH-DSA Public Keys in PKIX

In the X.509 certificate, the subjectPublicKeyInfo field has the SubjectPublicKeyInfo type, which has the following ASN.1 syntax:

    SubjectPublicKeyInfo  ::=  SEQUENCE  {
        algorithm         AlgorithmIdentifier,
        subjectPublicKey  BIT STRING
    }

The fields in SubjectPublicKeyInfo have the following meanings:

[I-D.draft-ietf-lamps-cms-sphincs-plus] defines the following public key identifiers for SLH-DSA:

   pk-slh-dsa-sha2-128s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-128s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-sha2-128f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-128f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-sha2-192s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-192s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-sha2-192f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-192f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-sha2-256s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-256s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-sha2-256f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-sha2-256f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-128s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-128s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-128f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-128f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-192s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-192s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-192f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-192f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-256s PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-256s
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   pk-slh-dsa-shake-256f PUBLIC-KEY ::= {
      IDENTIFIER id-alg-slh-dsa-shake-256f
      -- KEY no ASN.1 wrapping --
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
      -- PRIVATE-KEY no ASN.1 wrapping -- }

   SLH-DSA-PublicKey ::= OCTET STRING

Section 9.1 of [FIPS205] defines the raw octet string encoding of an SLH-DSA public key as the concatenation of the PK.seed and PK.root values. The octet string length is 2*n bytes, where n is 16, 24, or 32, depending on the parameter set. When used in a SubjectPublicKeyInfo type, the subjectPublicKey BIT STRING contains the raw octet string encodings of the public keys.

[I-D.draft-ietf-lamps-cms-sphincs-plus] defines the SLH-DSA-PublicKey ASN.1 OCTET STRING type for encoding a public key when not used in a SubjectPublicKeyInfo. The OCTET STRING is mapped to a subjectPublicKey (a value of type BIT STRING) as follows: the most significant bit of the OCTET STRING value becomes the most significant bit of the BIT STRING value, and so on; the least significant bit of the OCTET STRING becomes the least significant bit of the BIT STRING.

The id-alg-slh-dsa-* identifiers defined in Section 3 MUST be used as the algorithm field in the SubjectPublicKeyInfo sequence [RFC5280] to identify a SLH-DSA public key.

The following is an example of a [TODO: pick an OID] public key encoded using the textual encoding defined in [RFC7468].

-----BEGIN PUBLIC KEY-----
TODO
-----END PUBLIC KEY-----

Conforming CA implementations MUST specify the X.509 public key algorithm explicitly by using the OIDs specified in Section 3 when using SLH-DSA public keys in certificates and CRLs. Conforming client implementations that process SLH-DSA public keys when processing certificates and CRLs MUST recognize the corresponding OIDs.

6. Key Usage Bits

The intended application for the key is indicated in the keyUsage certificate extension; see Section 4.2.1.3 of [RFC5280]. If the keyUsage extension is present in a certificate that indicates an id-alg-slh-dsa-* identifier in the SubjectPublicKeyInfo, then the at least one of following MUST be present:

    digitalSignature; or
    nonRepudiation; or
    keyCertSign; or
    cRLSign.

Requirements about the keyUsage extension bits defined in [RFC5280] still apply.

7. Security Considerations

The security considerations of [RFC5280] applies accordingly.

Implementations MUST protect the private keys. Compromise of the private keys may result in the ability to forge signatures.

When generating an SLH-DSA key pair, an implementation MUST generate each key pair independently of all other key pairs in the SLH-DSA hypertree.

A SLH-DSA tree MUST NOT be used for more than 2^64 signing operations.

The generation of private keys relies on random numbers. The use of inadequate pseudo-random number generators (PRNGs) to generate these values can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. The generation of quality random numbers is difficult, and [RFC4086] offers important guidance in this area.

When computing signatures, the same hash function SHOULD be used to compute the message digest of the content and the signed attributes, if they are present.

When computing signatures, implementations SHOULD include protections against fault injection attacks [CMP2018],[SLotH]. Protections against these attacks include signature verification prior to releasing the signature value to confirm that no error injected and generating the signature a few times to confirm that the same signature value is produced each time.

8. IANA Considerations

For the ASN.1 Module in the Appendix of this document, IANA is requested to assign an object identifier (OID) for the module identifier (TBD1) with a Description of "id-mod-x509-slh-dsa-2024". The OID for the module should be allocated in the "SMI Security for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0).

9. References

9.1. Normative References

[FIPS205]
"TBD", n.d..
[FIPS205-ipd]
National Institute of Standards and Technology (NIST), "Stateless Hash-Based Digital Signature Standard", , <https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.205.ipd.pdf>.
[I-D.draft-ietf-lamps-cms-sphincs-plus]
Housley, R., Fluhrer, S., Kampanakis, P., and B. Westerbaan, "Use of the SLH-DSA Signature Algorithm in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-ietf-lamps-cms-sphincs-plus-06, , <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-cms-sphincs-plus-06>.
[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>.
[RFC5280]
Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, , <https://www.rfc-editor.org/rfc/rfc5280>.
[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>.

9.2. Informative References

[CMP2018]
Castelnovi, L., A, Martinelli, and T. Prest, "Grafting Trees: A Fault Attack Against the SPHINCS Framework", Lecture Notes in Computer Science vol 10786, PQCrypto 2018, Post-Quantum Cryptography pp. 165-184, , <https://link.springer.com/chapter/10.1007/978-3-319-79063-3_8>.
[FIPS180]
Dang, Q. H. and NIST, "Secure Hash Standard", NIST Federal Information Processing Standards Publications 180-4, DOI 10.6028/NIST.FIPS.180-4, , <https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf>.
[FIPS202]
Dworkin, M., Dworkin, M. J., and NIST, "SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions", FIPS PUB 202, NIST Federal Information Processing Standards Publications 202, DOI 10.6028/nist.fips.202, DOI 10.6028/NIST.FIPS.202, , <http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf>.
[I-D.ietf-lamps-dilithium-certificates]
Massimo, J., Kampanakis, P., Turner, S., and B. Westerbaan, "Internet X.509 Public Key Infrastructure: Algorithm Identifiers for ML-DSA", Work in Progress, Internet-Draft, draft-ietf-lamps-dilithium-certificates-03, , <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-dilithium-certificates-03>.
[NIST-PQC]
National Institute of Standards and Technology, "Post-Quantum Cryptography Project", , <https://csrc.nist.gov/projects/post-quantum-cryptography>.
[RFC4086]
Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, , <https://www.rfc-editor.org/rfc/rfc4086>.
[RFC7468]
Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, , <https://www.rfc-editor.org/rfc/rfc7468>.
[RFC8411]
Schaad, J. and R. Andrews, "IANA Registration for the Cryptographic Algorithm Object Identifier Range", RFC 8411, DOI 10.17487/RFC8411, , <https://www.rfc-editor.org/rfc/rfc8411>.
[SLotH]
Saarinen, M-J., "Accelerating SLH-DSA by Two Orders of Magnitude with a Single Hash Unit", , <https://eprint.iacr.org/2024/367.pdf>.

Appendix A. ASN.1 Module

RFC EDITOR: Please replace TBD2 with the value assigned by IANA during the publication of [I-D.draft-ietf-lamps-cms-sphincs-plus].

<CODE BEGINS>
X509-SLH-DSA-Module-2024
  { iso(1) identified-organization(3) dod(6) internet(1) security(5)
    mechanisms(5) pkix(7) id-mod(0) id-mod-x509-slh-dsa-2024(TBD1) }

DEFINITIONS IMPLICIT TAGS ::= BEGIN

EXPORTS ALL;

IMPORTS
  PUBLIC-KEY, SIGNATURE-ALGORITHM
    FROM AlgorithmInformation-2009  -- in [RFC5911]
    { iso(1) identified-organization(3) dod(6) internet(1)
      security(5) mechanisms(5) pkix(7) id-mod(0)
      id-mod-algorithmInformation-02(58) }

  pk-slh-dsa-sha2-128s, pk-slh-dsa-sha2-128f, pk-slh-dsa-sha2-192s,
  pk-slh-dsa-sha2-192f, pk-slh-dsa-sha2-256s, pk-slh-dsa-sha2-256f,
  pk-slh-dsa-shake-128s, pk-slh-dsa-shake-128f, pk-slh-dsa-shake-192s,
  pk-slh-dsa-shake-192f, pk-slh-dsa-shake-256s, pk-slh-dsa-shake-256f,
  sa-slh-dsa-sha2-128s, sa-slh-dsa-sha2-128f, sa-slh-dsa-sha2-192s,
  sa-slh-dsa-sha2-192f, sa-slh-dsa-sha2-256s, sa-slh-dsa-sha2-256f,
  sa-slh-dsa-shake-128s, sa-slh-dsa-shake-128f, sa-slh-dsa-shake-192s,
  sa-slh-dsa-shake-192f, sa-slh-dsa-shake-256s, sa-slh-dsa-shake-256f
    FROM SLH-DSA-Module-2024  -- in [I-D.draft-ietf-lamps-cms-sphincs-plus]
    { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
      id-smime(16) id-mod(0) id-mod-slh-dsa-2024(TBD2) } ;

--
-- Expand SignatureAlgorithms from RFC 5912
--
SignatureAlgorithms SIGNATURE-ALGORITHM ::= {
   sa-slh-dsa-sha2-128s |
   sa-slh-dsa-sha2-128f |
   sa-slh-dsa-sha2-192s |
   sa-slh-dsa-sha2-192f |
   sa-slh-dsa-sha2-256s |
   sa-slh-dsa-sha2-256f |
   sa-slh-dsa-shake-128s |
   sa-slh-dsa-shake-128f |
   sa-slh-dsa-shake-192s |
   sa-slh-dsa-shake-192f |
   sa-slh-dsa-shake-256s |
   sa-slh-dsa-shake-256f,
   ... }

--
-- Expand PublicKeyAlgorithms from RFC 5912
--
PublicKeyAlgorithms PUBLIC-KEY ::= {
   pk-slh-dsa-sha2-128s |
   pk-slh-dsa-sha2-128f |
   pk-slh-dsa-sha2-192s |
   pk-slh-dsa-sha2-192f |
   pk-slh-dsa-sha2-256s |
   pk-slh-dsa-sha2-256f |
   pk-slh-dsa-shake-128s |
   pk-slh-dsa-shake-128f |
   pk-slh-dsa-shake-192s |
   pk-slh-dsa-shake-192f |
   pk-slh-dsa-shake-256s |
   pk-slh-dsa-shake-256f,
   ... }

END

<CODE ENDS>

Appendix B. Security Strengths

Instead of defining the strength of a quantum algorithm in a traditional manner using precise estimates of the number of bits of security, NIST has instead elected to define a collection of broad security strength categories. Each category is defined by a comparatively easy-to-analyze reference primitive that cover a range of security strengths offered by existing NIST standards in symmetric cryptography, which NIST expects to offer significant resistance to quantum cryptanalysis. These categories describe any attack that breaks the relevant security definition that must require computational resources comparable to or greater than those required for: Level 1 - key search on a block cipher with a 128-bit key (e.g., AES128), Level 2 - collision search on a 256-bit hash function (e.g., SHA256/ SHA3-256), Level 3 - key search on a block cipher with a 192-bit key (e.g., AES192), Level 4 - collision search on a 384-bit hash function (e.g. SHA384/SHA3-384), Level 5 - key search on a block cipher with a 256-bit key (e.g., AES 256).

The parameter sets defined for NIST security levels 1, 3 and 5 are listed in Table 1, along with the resulting signature size, public key, and private key sizes in bytes.

Table 1: SLH-DSA security strengths
OID NIST Level Sig. Pub. Key Priv. Key
id-alg-slh-dsa-sha2-128s 1 7856 32 64
id-alg-slh-dsa-sha2-128f 1 17088 32 64
id-alg-slh-dsa-sha2-192s 3 16224 48 96
id-alg-slh-dsa-sha2-192f 3 35664 48 96
id-alg-slh-dsa-sha2-256s 5 29792 64 128
id-alg-slh-dsa-sha2-256f 5 49856 64 128
id-alg-slh-dsa-shake-128s 1 7856 32 64
id-alg-slh-dsa-shake-128f 1 17088 32 64
id-alg-slh-dsa-shake-192s 3 16224 48 96
id-alg-slh-dsa-shake-192f 3 35664 48 96
id-alg-slh-dsa-shake-256s 5 29792 64 128
id-alg-slh-dsa-shake-256f 5 49856 64 128

Acknowledgments

Much of the structure and text of this document is based on [I-D.ietf-lamps-dilithium-certificates]. The remainder comes from [I-D.draft-ietf-lamps-cms-sphincs-plus]. Thanks to those authors, and the ones they based their work on, for making our work earier. "Copying always makes things easier and less error prone" - [RFC8411].

Authors' Addresses

Kaveh Bashiri
BSI
Scott Fluhrer
Cisco Systems
Stefan Gazdag
genua GmbH
Daniel Van Geest
CryptoNext Security
Stavros Kousidis
BSI