refactor(stm): update PoP, protocol parameters and decoding functions

[damrobi]

Content

This PR includes an update to the handling of the proof of possession of BLS keys, a modification of the checks done on the protocol parameters and a modification to the decoding function of the merkle tree path and concatenation proof.

Changes

• Add checked arithmetic to legacy byte decoders (Merkle tree, batch commitment, ConcatenationProof, SingleSignature)
• Validate phi_f is within (0, 1] before use in lottery/eligibility computations
• Restrict KeyRegistration::register_by_entry to pub(crate) so external registration must go through register(), which always verifies proof of possession
• Make ClosedKeyRegistration fields private with a pub(crate) constructor
• Narrow RegistrationEntry/ClosedRegistrationEntry (types, constructors, methods) to pub(crate) and dropped RegistrationEntry's unused Serialize/Deserialize
• Fix resulting lint warnings: #[allow(private_interfaces)] where a public error/field intentionally carries a now-private type, #[cfg(test)] on Merkle tree byte (de)serialization helpers that are test-only

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

Comments

Issue(s)

[github-actions]

Test Results

     5 files  ± 0     209 suites  ±0   1h 37m 49s ⏱️ - 59m 2s
 3 334 tests  - 54   3 334 ✅  - 54  0 💤 ±0  0 ❌ ±0 
11 072 runs   - 54  11 072 ✅  - 54  0 💤 ±0  0 ❌ ±0 

Results for commit 917a568. ± Comparison against base commit 2eedbd2.

This pull request removes 56 and adds 2 tests. Note that renamed tests count towards both.

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
…

mithril-stm ‑ proof_system::concatenation::eligibility::tests::is_lottery_won_rejects_out_of_range_phi_f
mithril-stm ‑ proof_system::halo2_snark::eligibility::tests::compute_target_value_for_snark_lottery_rejects_out_of_range_phi_f

♻️ This comment has been updated with latest results.