As mentioned in our article last month about NIST’ Round 3 selection for Post Quantum Cryptography (PQC) algorithms, they are now formally issuing a call for additional PQC algorithms to use for digital signatures. In Round 3, they did select CRYSTALS-Dilithium, Falcon, and SPHINCS+ for use as quantum resistant digital signatures. CRYSTALS-Dilithium and Falcon are based upon a structured lattice class of algorithms while SPHINCS+ uses a stateless hash-based signature scheme. However, weaknesses were found in Rainbow and a few other algorithms and they were eliminated from further consideration. As a result, NIST has no additional digital signature candidates to evaluate during Round 4. For comparison, NIST selected four Key Encapsulation/Encryption algorithms for evaluation in Round 4 and potential future standardization.

NIST is concerned that the three digital signature algorithms selected in Round 3 do not provide enough diversity for protection against possible weaknesses that might be found in the future. Their primary interest is to identify general-purpose signature schemes that are not based on structured lattices. And for certain applications, such as certificate transparency, NIST may also be interested in signature schemes that have short signatures and fast verification. Although NIST won’t reject out of hand a submission of a new lattice based algorithm, it would need to provide a considerable improvement in either performance or security properties over CRYSTALS-Dilitihum and Falcon to be considered.

NIST has established a final deadline of June 1, 2023 for parties to submit new digital signature algorithms for consideration. But they also indicated that any submission packages submitted by March 1, 2023 will be reviewed for deficiencies with a notification by March 31, 2023 if any are found. This would provide the submitter with about 60 days to correct any deficiencies before the final deadline. You can view a summary of NIST’s Call for Proposal on a web page here and the detailed document describing their criteria and procedures for making a submission here.

September 7, 2022