Derandomize RPO-STARK DSA

[Al-Kindi-0]

Describe your changes

Derandomizes the RPO-STARK DSA in a similar manner to the proposal RFC6979 for ECDSA.

Once the issue of how to seed the salted Merkle tree vector commitment scheme in Winterfell is solved then this will be ready for review.

Checklist before requesting a review

• Repo forked and branch created from next according to naming convention.
• Commit messages and codestyle follow conventions.
• Relevant issues are linked in the PR description.
• Tests added for new functionality.
• Documentation/comments updated according to changes.

[bobbinth]

Question not related to this PR: could the same methodology be used to make Falcon signature deterministic? Or is there something about the Flacon signatures that make it inherently impossible to do this.

[Al-Kindi-0]

Question not related to this PR: could the same methodology be used to make Falcon signature deterministic? Or is there something about the Flacon signatures that make it inherently impossible to do this.

Yes, the same principle can be applied to Falcon as well though it will require a bit of care as signature generation uses a delicate sampling procedure and we would have to derandomize it fully. The key thing that we would have to insure is that the floating point arithmetic is stable across platforms, this is in addition to the need to build the seed using the above methodology.
One more thing that we will have to guard against is hashing to the same point the message when anything about the signature generation procedure changes (e.g., bug, optimization, etc). A solution to this could be to either change the secret key whenever something about the signature procedure changes or use a versioned hash-to-map procedure.

The above is well explained here especially Section 2 and the issue of robustness across devices of the sampling procedure is analyzed in Section 3.4.2.

So the short answer is yes we can do it but we have to be more careful than the above.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bobbinth]

Looks good! Thank you!