feat(stm): enable plutus friendly hash

[damrobi]

Content

This PR includes a switch of the Blake2b transcript hash function used when generating IVC proofs. The current implementation a version of Blake2b-512 that is not Plutus friendly. The latest update of MidnightZK introduced a Blake2b256 which is Plutus friendly and can be used as a transcript hash. More details in this discussion.

Changes:

All blake2b_simd::State uses were replaced by Blake2b256 and the test assets were regenerated.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
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Comments

Issue(s)

Closes #3307

[github-actions]

Test Results

     5 files  ± 0     209 suites  ±0   1h 36m 14s ⏱️ - 1h 38m 31s
 3 334 tests  - 51   3 334 ✅  - 51  0 💤 ±0  0 ❌ ±0 
11 066 runs   - 54  11 066 ✅  - 54  0 💤 ±0  0 ❌ ±0 

Results for commit 3585373. ± Comparison against base commit e5f3c86.

This pull request removes 51 tests.

mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::index_out_of_bounds
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::index_too_large_for_circuit_range
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::indices_not_increasing
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_merkle_path_mismatch
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_swap_keep_merkle_path
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_wrong_verification_key
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_corrupt_sibling
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_flip_position
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_length_long
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_length_short
…

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

This PR updates the IVC transcript hash used by the experimental SNARK (future_snark) path to a Plutus-friendly Blake2b variant by switching from blake2b_simd::State to midnight_proofs::transcript::Blake2b256, and regenerates associated test assets.

Changes:

• Replace all blake2b_simd::State transcript usages with Blake2b256 across IVC proof generation and aggregate signature plumbing.
• Update circuit test utilities to use Sha256 for shared-cache fingerprinting and remove blake2b_simd dependency entries from mithril-stm.
• Adjust IVC test/generator code to use the new transcript hash type.

Reviewed changes

Copilot reviewed 6 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mithril-stm/src/protocol/aggregate_signature/signature.rs	Switch IVC aggregate-signature variant and helpers/tests to IvcProof<Blake2b256>.
mithril-stm/src/protocol/aggregate_signature/clerk.rs	Update IVC proving pipeline return type to IvcProof<Blake2b256>.
mithril-stm/src/proof_system/ivc_halo2_snark/proof.rs	Use Blake2b256 transcript for IVC proof generation and update tests accordingly.
mithril-stm/src/circuits/test_utils/file_mutex.rs	Replace Blake2b-based cache fingerprinting with Sha256 + hex::encode.
mithril-stm/src/circuits/halo2_ivc/tests/common/generators/proofs.rs	Update test proof generation/verification helpers to use Blake2b256.
mithril-stm/Cargo.toml	Remove blake2b_simd optional/dev dependency wiring from future_snark.
Cargo.lock	Drop blake2b_simd from the mithril-stm dependency list.

Comments suppressed due to low confidence (1)

mithril-stm/src/proof_system/ivc_halo2_snark/proof.rs:392

• The local variable blake2b_bytes is now produced with the Blake2b256 transcript hash, so the name is misleading (it previously implied the older Blake2b variant). Renaming it to blake2b256_bytes (or similar) will make the transcript choice explicit and reduce confusion when reading/debugging proof generation.

        let blake2b_bytes = IvcProof::<Blake2b256>::prove_with_transcript(
            &self.ivc_setup.srs,
            &self.ivc_setup.ivc_proving_key,
            &circuit_data,
            &public_inputs,
            &mut self.rng,
        )?;
        let proof = IvcProof::new(
            IvcProofBytes::new(blake2b_bytes),
            prover_input.next_state,
            prover_input.next_accumulator,
        );

[jpraynaud]

LGTM 👍