FN-DSA for JOSE and COSE

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Table of Contents

1. Introduction

This document specifies JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE) serializations for FFT (fast-Fourier transform) over NTRU-Lattice-Based Digital Signature Algorithm (FN-DSA), a Post-Quantum Cryptography (PQC) digital signature scheme defined in US NIST FIPS 206 (expected to be published in late 2026 early 2027).¶

FN-DSA (formerly known as Falcon) is a lattice-based digital signature scheme based on the GPV hash-and-sign framework [GPV08], instantiated over NTRU lattices with fast Fourier sampling techniques [DP16]. The core hard problem underlying FN-DSA is the SIS (Short Integer Solution) problem over NTRU lattices.¶

FN-DSA (formerly known as Falcon) is a digital signature algorithm based on lattice mathematics. It follows the hash-and-sign design introduced by Gentry, Peikert, and Vaikuntanathan [GPV08]. FN-DSA operates on NTRU lattices and uses fast Fourier techniques [DP16] to make signature generation compact and efficient. The security of the scheme relies on the hardness of solving certain lattice problems, in particular the Short Integer Solution (SIS) problem.¶

FN-DSA offers:¶

• Post-quantum security under the assumption that NTRU-SIS remains hard.¶

• Compactness in key and signature size.¶

• Efficient operations (roughly O(n log n)).¶

• A requirement for careful implementation to avoid side-channel leakage (notably Gaussian sampling must be constant-time where applicable).¶

The sizes of public key, private key, and signature for the parameter sets are the same as in the original Falcon specification:¶

For a detailed comparison of FN-DSA with ML-DSA [USNIST.FIPS.204] and SLH-DSA [USNIST.FIPS.205] see Section 11.3 of [I-D.draft-ietf-pquip-pqc-engineers].¶

This document defines how FN-DSA is used with JSON Object Signing and Encryption (JOSE) [RFC7515] and CBOR Object Signing and Encryption (COSE) [RFC9052] [RFC9053].¶

2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. The FN-DSA Algorithm Family

The FN-DSA Signature Scheme is parameterized to support different security levels.¶

This document introduces the registration of the following algorithms in [IANA.jose]:¶

This document introduces the registration of the following algorithms in [IANA.cose]:¶

4. FN-DSA Keys

The FN-DSA Algorithm Family uses the Algorithm Key Pair (AKP) key type, as defined in [I-D.draft-ietf-cose-dilithium].¶

The specific algorithms for FN-DSA, such as FALCON512 and FALCON1024, are defined in this document and are used in the alg value of an AKP key representation to specify the corresponding algorithm.¶

Thumbprints for FN-DSA keys are computed according to the process described in [I-D.draft-ietf-cose-dilithium].¶

5. Security Considerations

The security considerations of [RFC7515], [RFC7517] and [RFC9053] apply to this specification as well.¶

A detailed security analysis of FN-DSA is beyond the scope of this specification; see [USNIST.FIPS.206] for additional details.¶

All the usual caveats for PQC and side-channel resistance apply.¶

• Implementations MUST ensure that alg matches the intended algorithm variant.¶

• Private implementations of sampling (Gaussian, etc.) must be constant-time to prevent leakage.¶

• Public keys SHOULD be validated before use (e.g., against encoding constraints).¶

• Nonces, random values, blinding factors (if used) MUST originate from a secure source of randomness.¶

6. IANA Considerations

7. References

Appendix A. Examples

{
  "kty": "AKP",
  "alg": "FN-DSA-512",
  "pub": "V53SIdVF...uvw2nuCQ",
  "priv": "V53SIdVF...cDKLbsBY"
}

{
  "kty": "AKP",
  "alg": "FN-DSA-512",
  "pub": "V53SIdVF...uvw2nuCQ"
}

{
  "kid: "clpwZ...RWYU9CUF",
  "alg": "FN-DSA-512",
  "typ": "JWT"
}

{
  / kty AKP        / 1: 7,
  / alg FN-DSA-512 / 3: -54,
  / public key     / -1: h'7803c0f9...3f6e2c70',
  / private key    / -2: h'7803c0f9...3bba7abd'
}

{
  / kty AKP         / 1: 7,
  / alg FN-DSA-512  / 3: -54,
  / public key      / -1: h'7803c0f9...3f6e2c70',
}

18([
  <<{
    / alg FN-DSA-512 / 1: -54,
  }>>,
  / unprotected / {},
  / payload / h'66616b65',
  / signature / h'53e855e8...0f263549'
])

Appendix B. Document History

-02¶

• Converted to markdown¶

• Applied feedback from IESG Evaluation on ML-DSA¶

• Revised references¶

• Revised abstract¶

-01¶

• Added Acknowledgements¶

• Added Document History¶

• Updated test vectors¶

Acknowledgments

We would like to especially thank David Balenson for careful review of approaches taken in this document. We would also like to thank Michael B. Jones for guidance in authoring.¶

Contributors

Authors' Addresses