feat(eddsa): Bandersnatch in Assign helpers, re-enable the Bandersnat…

[rdubois-crypto]

Depends on Consensys-Incorporated/gnark-crypto#882

Description

Solve an incorrect import that drag Jujub instead of Bandersnatch. See also issue 881

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Note

Medium Risk
Touches EdDSA witness decoding for a new curve; incorrect parsing would break or mis-verify circuits, but the change is narrow and covered by re-enabled tests.

Overview
Adds Bandersnatch (BLS12-381) support for decompressing public keys and signatures in the std EdDSA Assign path, and bumps gnark-crypto to pick up the matching curve definitions (Consensys-Incorporated/gnark-crypto#882).

parseSignature and parsePoint now handle tedwards.BLS12_381_BANDERSNATCH using ecc/bls12-381/bandersnatch point types instead of the wrong Jubjub/twisted-Edwards import (issue #881). The integration test for Bandersnatch + MiMC is turned back on, with forge-test offset handling aligned to the other 32-byte curves.

^{Reviewed by Cursor Bugbot for commit a0d0387. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Copilot]

🟢 Approval recommended

No unresolved issues were identified, and the supplied assessments support approval.

Pull request overview

Adds Bandersnatch support to EdDSA key and signature decoding, with renewed integration-test coverage.

Changes:

• Decode Bandersnatch compressed points using the correct package.
• Support Bandersnatch signature scalar offsets.
• Re-enable Bandersnatch EdDSA tests.

File summaries

File	Changes
std/signature/eddsa/eddsa.go	Adds Bandersnatch point and signature parsing.
std/signature/eddsa/eddsa_test.go	Re-enables Bandersnatch EdDSA tests.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[ivokub]

Depends on Consensys-Incorporated/gnark-crypto#882

Description

Solve an incorrect import that drag Jujub instead of Bandersnatch. See also issue 881

Note

Medium Risk Changes live in signature parsing and witness assignment for a new curve ID; mistakes could break in-circuit verification for Bandersnatch, but the change mirrors existing curve branches and adds test coverage.

Overview Adds Bandersnatch (BLS12_381_BANDERSNATCH) to the EdDSA circuit helpers that decode compressed binary keys and signatures into witness fields.

parsePoint and parseSignature now import and use gnark-crypto/ecc/bls12-381/bandersnatch (instead of the wrong Jubjub/twisted Edwards path) with the same 32-byte compressed layout as BLS12-381 twisted Edwards. Tests re-enable the Bandersnatch MiMC configuration and teach the signature-forge helper the 32-byte S offset for that curve ID.

Depends on Consensys-Incorporated/gnark-crypto#882.

Reviewed by Cursor Bugbot for commit 12fb2c5. Bugbot is set up for automated code reviews on this repo. Configure here.

Thanks for the PR!

gnark-crypto now has the fix, can you also go get github.com/consensys/gnark-crypto@master in this branch? I don't have push permissions to fix it.

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	golang/​github.com/​consensys/​gnark-crypto@​v0.21.1-0.20260912000500-b6021c71b163 ⏵ v0.21.1-0.20260913224755-1409fe592052	+1

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[rdubois-crypto]

Done: rebased on master and bumped gnark-crypto to master (go get github.com/consensys/gnark-crypto@master, the pseudo-version carrying #882). TestEddsa passes locally including the re-enabled Bandersnatch configuration; the CodeQL job should be green too now.

[ivokub]

Yep, looks good -- the tests pass locally for me as well. The failing CI test is due to code generation update which updates the included testing tinyfield package. I'll address it in a separate PR.