feat(stm): Verify SNARK proof

[damrobi]

Content

This PR includes the addition of a proof.rs module in proof_system/halo2_snark/ that contains a SnarkProof structure and a verify function to verify the proof. The structure and function follow a similar style to the concatenation proof. For now, the verify function loads/generates the srs and generates the verification_key on the fly in the function itself.

I left some non-doc comments in the code that we can discuss and remove as you deem necessary. The names are also up for debate as I used Snark to prefix the structure and constants but we could go for Halo2Snark or something more precise,

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
  • Reviewer requested
• Documentation
  • No new TODOs introduced

Comments

Issue(s)

Relates to #3041

[github-actions]

Test Results

    5 files  ±0    201 suites  ±0   1h 16m 5s ⏱️ + 7m 42s
2 810 tests +8  2 810 ✅ +8  0 💤 ±0  0 ❌ ±0 
9 908 runs  +8  9 908 ✅ +8  0 💤 ±0  0 ❌ ±0 

Results for commit 96e4430. ± Comparison against base commit d0e7a3d.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Adds initial SNARK proof verification support to the mithril-stm Halo2 SNARK proof system (feature-gated by future_snark), by introducing a SnarkProof type and a verify entry point similar in spirit to the existing concatenation proof flow.

Changes:

• Introduces halo2_snark::proof module with SnarkProof + verification logic (including temporary SRS/VK derivation inside verify).
• Adds SNARK_PROOF_LENGTH constant to halo2_snark module.
• Adds new crate dependencies needed by the verifier path (blake2b_simd, rand_chacha).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 14 comments.

File	Description
mithril-stm/src/proof_system/halo2_snark/proof.rs	New SNARK proof container, SRS loading/generation helper, and verify implementation (+ feature-gated tests).
mithril-stm/src/proof_system/halo2_snark/mod.rs	Wires in the new proof submodule and defines the proof byte-length constant.
mithril-stm/Cargo.toml	Adds dependencies required by the new verification implementation.

[hjeljeli32]

Looks a very good step towards the SNARK path in STM, and the proof generation/verification tests are useful. I left a couple of non-blocking comments probably more relevant when we wire the E2E path and move to product-ready code.

[jpraynaud]

LGTM 👍

I just left few minor comments to be addressed before merging.

[curiecrypt]

Nice work!
The test coverage is thorough: roundtrip, wrong message, wrong params, random bytes, serialization, and golden test cover the important cases well. The CircuitVerificationKey wrapper with custom serde is clean. The verify function signature is straightforward and consistent with the concatenation proof style.

I left a few comments on minor issues.

LGTM 🚀