feat: SNARK-friendly protocol message by jpraynaud · Pull Request #3254 · input-output-hk/mithril

jpraynaud · 2026-05-05T15:46:26Z

Content

This PR includes a SNARK-friendly variant of the ProtocolMessage so its hash can be opened in the IVC circuit, while keeping the legacy hash scheme byte-identical for backward compatibility:

New ProtocolMessageHashScheme (Legacy, Rigid) on ProtocolMessage. Legacy stays the default and serializes without the field (pre-Lagrange wire shape preserved).
Rigid scheme assembles a fixed-size labeled preimage: digest || next_aggregate_verification_key || next_protocol_parameters || current_epoch (190 bytes total).
SignableBuilderService becomes era-aware: Pythagoras keeps Legacy, Lagrange flips to Rigid and runs check_rigid_integrity before signing.
Everything rigid-specific is gated behind the future_snark feature.

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

One new TODO is intentional: to_rigid_slot_bytes writes 4 zero bytes between the Merkle root and total_stake to mirror the IVC test fixture's leaf-count slot.

Issue(s)

Closes #3146

Copilot

Pull request overview

This PR introduces a SNARK-friendly (“rigid”) variant of ProtocolMessage hashing to support opening the protocol-message hash inside the IVC circuit, while preserving byte-identical legacy hashing/serialization for pre-Lagrange certificates. Activation is era-driven (Pythagoras → Legacy, Lagrange → Rigid) and rigid-specific behavior is gated behind the future_snark feature.

Changes:

Add ProtocolMessageHashScheme (Legacy default, Rigid) and implement rigid labeled-preimage hashing + integrity checks (feature-gated).
Add rigid-slot encodings for SNARK AVK (44 bytes) and protocol parameters (32 bytes) with stability tests.
Make SignableBuilderService era-aware: enforce SNARK AVK presence + rigid integrity in Lagrange; add verifier tests covering rigid dispatch and era transition.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
mithril-stm/src/protocol/parameters.rs	Adds a 32-byte rigid-slot encoding for protocol parameters (feature-gated) + golden tests.
mithril-stm/src/proof_system/halo2_snark/aggregate_key.rs	Adds a 44-byte rigid-slot projection for SNARK AVK + golden test.
mithril-aggregator/src/services/signable_builder/signable_seed_builder.rs	Adds era discovery (`compute_current_era`) for Lagrange/Pythagoras dispatch (feature-gated).
mithril-signer/src/services/signable_builder/signable_seed_builder.rs	Adds era discovery (`compute_current_era`) for Lagrange/Pythagoras dispatch (feature-gated).
mithril-common/src/signable_builder/interface.rs	Extends `SignableSeedBuilder` with `compute_current_era` under `future_snark`.
mithril-common/src/signable_builder/signable_builder_service.rs	Era-aware selection of rigid hashing in Lagrange + rigid integrity check before returning the message.
mithril-common/src/entities/protocol_message.rs	Implements `ProtocolMessageHashScheme`, rigid preimage assembly/hashing, and rigid integrity validation (feature-gated).
mithril-common/src/entities/mod.rs	Updates entities re-exports to include new protocol-message types.
mithril-common/src/certificate_chain/certificate_verifier.rs	Adds tests ensuring verifier logic accepts rigid protocol messages and era-transition chaining behavior.

github-actions · 2026-05-05T15:59:20Z

Test Results

5 files ± 0 203 suites ±0 1h 1m 23s ⏱️ - 3h 37m 12s
3 054 tests + 3 3 054 ✅ + 3 0 💤 ±0 0 ❌ ±0
10 459 runs +24 10 459 ✅ +24 0 💤 ±0 0 ❌ ±0

Results for commit 781f2ef. ± Comparison against base commit e0ad33f.

This pull request removes 54 and adds 57 tests. Note that renamed tests count towards both.

mithril-common ‑ entities::protocol_message::tests::test_protocol_message_compute_hash_include_lastest_immutable_file_number
mithril-common ‑ entities::protocol_message::tests::test_protocol_message_compute_hash_the_same_hash_with_same_protocol_message
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-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::aggregate_verification_key_chain_dispatches_to_concatenation_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::concatenation_aggregate_verification_key_chains_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::epoch_chain_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::predecessor_uses_legacy_hash_scheme_and_successor_uses_rigid_hash_scheme
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::previous_hash_chain_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::protocol_parameters_chain_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::snark_signature_dispatch::aggregate_verification_key_chain_dispatches_to_snark_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::era_transition_chain_linkage::snark_signature_dispatch::snark_aggregate_verification_key_chains_at_era_transition
mithril-common ‑ certificate_chain::certificate_verifier::tests::rigid_protocol_message_dispatch::verify_epoch_matches_protocol_message_accepts_rigid_variant_when_epoch_matches
mithril-common ‑ certificate_chain::certificate_verifier::tests::rigid_protocol_message_dispatch::verify_epoch_matches_protocol_message_rejects_rigid_variant_when_epoch_mismatches
…

♻️ This comment has been updated with latest results.

turmelclem

LGTM

Alenar

LGTM

jpraynaud · 2026-05-07T16:26:44Z

Hi @curiecrypt @hjeljeli32 @damrobi could you review the cryptographic part?

mithril-common/src/entities/protocol_message.rs
mithril-stm/*

hjeljeli32

LGTM 👍 . I just left one comment about the behavior of rigid_preimage function.

And become SNARK-friendly so that its hash can be opened in the IVC circuit.

…grange era transition Cover concatenation AVK, SNARK AVK, protocol parameters, epoch and previous-hash chaining when the predecessor uses the legacy hash scheme (Pythagoras) and the successor uses the rigid hash scheme (Lagrange).

…nark'

… 'future_snark'

…EraFetcher' trait Instead of having 'SignableSeedBuilder' trait supporting it.

* mithril-era from `0.1.8` to `0.1.9` * mithril-aggregator from `0.8.50` to `0.8.51` * mithril-common from `0.6.71` to `0.6.72` * mithril-signer from `1.0.0` to `1.0.1` * mithril-stm from `0.10.16` to `0.10.17`

jpraynaud self-assigned this May 5, 2026

Copilot AI review requested due to automatic review settings May 5, 2026 15:46

jpraynaud marked this pull request as draft May 5, 2026 15:46

Copilot started reviewing on behalf of jpraynaud May 5, 2026 15:47 View session

github-advanced-security AI found potential problems May 5, 2026

View reviewed changes

Comment thread mithril-common/src/entities/protocol_message.rs Fixed

Comment thread mithril-stm/src/proof_system/halo2_snark/aggregate_key.rs Fixed

Comment thread mithril-stm/src/protocol/parameters.rs Fixed

Copilot AI reviewed May 5, 2026

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jpraynaud temporarily deployed to testing-preview May 5, 2026 16:01 — with GitHub Actions Inactive

jpraynaud force-pushed the jpraynaud/3146-snark-friendly-protocol-message branch from 645abc6 to 825856e Compare May 5, 2026 16:04

jpraynaud temporarily deployed to testing-preview May 5, 2026 16:21 — with GitHub Actions Inactive

jpraynaud marked this pull request as ready for review May 6, 2026 08:11

jpraynaud requested review from Alenar and turmelclem May 6, 2026 08:12

jpraynaud temporarily deployed to testing-preview May 6, 2026 10:51 — with GitHub Actions Inactive

turmelclem approved these changes May 6, 2026

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Alenar approved these changes May 6, 2026

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Comment thread mithril-common/src/signable_builder/interface.rs Outdated

jpraynaud force-pushed the jpraynaud/3146-snark-friendly-protocol-message branch from 8ba311f to 3c015d2 Compare May 7, 2026 16:19

jpraynaud requested review from curiecrypt, damrobi and hjeljeli32 May 7, 2026 16:25

jpraynaud temporarily deployed to testing-preview May 7, 2026 16:37 — with GitHub Actions Inactive

hjeljeli32 approved these changes May 11, 2026

View reviewed changes

Comment thread mithril-common/src/entities/protocol_message.rs

jpraynaud added 7 commits May 11, 2026 09:37

feat(common): update ProtocolMessage to support multiple hash schemes

53cda4d

And become SNARK-friendly so that its hash can be opened in the IVC circuit.

tests(common): test ProtocolMessage chaining for hash schemes

b678ba9

feat(common): add era awareness for SignableBuilder

efe22d6

feat(aggregator): add era awareness for signable builder

bd99649

feat(signer): add era awareness for signable builder

edf0e2f

feat(common): check rigid layout integrity in the signable builder

72bab50

jpraynaud added 9 commits May 11, 2026 09:37

feat(common): gate the rigid protocol message scheme behind 'future_s…

3fdd565

…nark'

feat(stm): project SNARK AVK to a 44-bytes rigid slot

3b87658

chore: apply review comments

f41b29e

refactor(common): enhance readability of rigid ProtocolMessage

10f320f

tests(common): add golden tests for ProtocolMessage

e909178

refactor(common): gate Rigid scheme variant of ProtocolMessage behind…

f7c7de3

… 'future_snark'

refactor: move era fetching responsibility to 'SignableBuilderService…

a2c31d5

…EraFetcher' trait Instead of having 'SignableSeedBuilder' trait supporting it.

docs: update CHANGELOGs

3a6061f

chore: upgrade crate versions

781f2ef

* mithril-era from `0.1.8` to `0.1.9` * mithril-aggregator from `0.8.50` to `0.8.51` * mithril-common from `0.6.71` to `0.6.72` * mithril-signer from `1.0.0` to `1.0.1` * mithril-stm from `0.10.16` to `0.10.17`

jpraynaud force-pushed the jpraynaud/3146-snark-friendly-protocol-message branch from 3c015d2 to 781f2ef Compare May 11, 2026 10:09

jpraynaud temporarily deployed to testing-preview May 11, 2026 10:45 — with GitHub Actions Inactive

jpraynaud merged commit afdbf61 into main May 12, 2026
89 of 90 checks passed

jpraynaud deleted the jpraynaud/3146-snark-friendly-protocol-message branch May 12, 2026 12:36

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feat: SNARK-friendly protocol message#3254

feat: SNARK-friendly protocol message#3254
jpraynaud merged 16 commits into
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jpraynaud commented May 5, 2026 •

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