Implementation of Schnorr signature module for mithril-stm. #2761

damrobi · 2025-11-03T12:42:32Z

Content

This PR includes a new module for mithril-stm containing an implementation for the Schnorr signature that will be used in the SNARK version of mithril.

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
- Update README file (if relevant)
- Update documentation website (if relevant)
- Add dev blog post (if relevant)
- Add ADR blog post or Dev ADR entry (if relevant)
- No new TODOs introduced

Comments

Issue(s)

Relates to #2756

github-advanced-security

cargo-doc found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

github-advanced-security

clippy found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

github-actions · 2025-11-05T08:31:17Z

Test Results

4 files ±0 168 suites ±0 22m 55s ⏱️ -46s
2 210 tests ±0 2 210 ✅ ±0 0 💤 ±0 0 ❌ ±0
6 895 runs ±0 6 895 ✅ ±0 0 💤 ±0 0 ❌ ±0

Results for commit 40c68d6. ± Comparison against base commit b9f2466.

♻️ This comment has been updated with latest results.

mithril-stm/src/schnorr_signature/signing_key.rs

curiecrypt

First batch of reviews. It looks good at first glance.

mithril-stm/Cargo.toml

mithril-stm/src/schnorr_signature/mod.rs

mithril-stm/src/schnorr_signature/signing_key.rs

mithril-stm/src/schnorr_signature/verification_key.rs

mithril-stm/src/schnorr_signature/signature.rs

mithril-stm/Cargo.toml

jpraynaud · 2025-11-12T08:27:28Z

mithril-stm/src/schnorr_signature/mod.rs

+// TODO: Remove
+#![allow(dead_code)]


We want the code to be as TODO free as possible.

You can use public visibility to avoid the dead code warnings that we don't want to keep when merged.

actually, I suggested this to be removed when we are finished with all tasks of this PR.

jpraynaud · 2025-11-12T08:40:04Z

mithril-stm/src/schnorr_signature/mod.rs

+use midnight_circuits::{
+    ecc::{hash_to_curve::HashToCurveGadget, native::EccChip},
+    hash::poseidon::PoseidonChip,
+    types::AssignedNative,
+};
+use midnight_curves::{
+    Fq as JubjubBase, Fr as JubjubScalar, JubjubAffine, JubjubExtended, JubjubSubgroup,
+};
+use sha2::{Digest, Sha256};
+
+use anyhow::{Result, anyhow};
+
+mod signature;
+mod signing_key;
+mod verification_key;
+
+use signature::*;
+// use signing_key::*;
+use verification_key::*;


You should separate the module declaration from the imports and put the imports after. It is usually a good practice to create a new module inline to do that(you can refer to other files in the repository). A better option would be to move all this code in a new separate module like utils.

mithril-stm/src/schnorr_signature/mod.rs

mithril-stm/src/schnorr_signature/signature.rs

mithril-stm/src/schnorr_signature/signing_key.rs

mithril-stm/src/schnorr_signature/mod.rs

… one.

…ons.

…ption.

…e_snark feature.

… it is not published.

…n from schnorr signature.

curiecrypt

You should use full names even in function parameters. For example verification_key instead of vk.
For simplicity and descriptiveness, we can use random_scalar_1 instead of random_value_1. Consequently, we can call the generator * random_scalar_1 as random_point_1.
This will apply for all cases where we obtain a curve point by multiplying the generator with a scalar: For example: point_signature = generator * signature.
This kind of naming seems more descriptive and pleasant.
Final remark, if you use an underscore for separating numbers in one place, then you should do the same for all other similar cases. It should apply for separating x and y as well.

mithril-stm/src/schnorr_signature/signature.rs

curiecrypt · 2025-11-19T14:19:47Z

mithril-stm/src/schnorr_signature/signature.rs

+        // Computing R1 = H(msg) * s + sigma * c
+        let hash_msg_times_sig = hash_msg * self.signature;
+        let sigma_times_challenge = self.sigma * self.challenge;
+        let random_value_1_recomputed = hash_msg_times_sig + sigma_times_challenge;


We can use random_scalar_1, random_scalar_2. WDYT? @damrobi @jpraynaud

I think scalar is fine, it's more descriptive

Actually those values are points, so as you said in an other comment maybe random_point_1 would be better?

mithril-stm/src/schnorr_signature/mod.rs

curiecrypt · 2025-11-19T14:38:14Z

mithril-stm/src/schnorr_signature/mod.rs

+// TODO: Remove
+#![allow(dead_code)]


actually, I suggested this to be removed when we are finished with all tasks of this PR.

…nature.

damrobi added the feature 🚀 New implemented feature label Nov 3, 2025

damrobi force-pushed the damrobi/stm-add-schnorr-sig-module branch from b254ad2 to 1e07c07 Compare November 5, 2025 08:22

github-advanced-security bot found potential problems Nov 5, 2025

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damrobi changed the title ~~Added file structure for Schnorr signature module.~~ Implementation of Schnorr signature module for mithril-stm. Nov 6, 2025

github-advanced-security bot found potential problems Nov 6, 2025

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damrobi requested review from curiecrypt and jpraynaud November 7, 2025 13:31

damrobi temporarily deployed to testing-preview November 7, 2025 16:45 — with GitHub Actions Inactive

curiecrypt reviewed Nov 10, 2025

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damrobi temporarily deployed to testing-preview November 11, 2025 09:55 — with GitHub Actions Inactive

jpraynaud reviewed Nov 12, 2025

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github-advanced-security bot found potential problems Nov 12, 2025

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mithril-stm/src/schnorr_signature/mod.rs Fixed Show fixed Hide fixed

damrobi temporarily deployed to testing-preview November 13, 2025 12:59 — with GitHub Actions Inactive

damrobi added 14 commits November 17, 2025 12:33

Added file structure for Schnorr signature module.

6b7f3cf

Added to/from bytes for SchnorrSignature and started adding tests.

d6f792e

Moved test out of proptest.

de3a90f

Added more test and helper function to convert msg to base field.

469787c

applied clippy.

c3e3ee3

Cargo.lock change.

4827d96

Update msg to base field conversion.

979bb30

Add to and from bytes for SchnorrSignature.

5c20d3e

Removed prototype implementation of schnorr signature and started new…

54c3d6d

… one.

Added generate function for Schnorr signature.

20f29aa

Added conversion from sk to vk for use in signature.

8bb1976

Added helper function for converting a message to jubjub base field.

4c8409f

Added sign function for SchnorrSigningKey and necessary helper functi…

ba45d31

…ons.

Added test function for get_coordinates and fix the sign function.

def6d05

damrobi added 17 commits November 17, 2025 12:33

Added verification function and tests to signature.

a5931d7

Removed unused dependency.

bf1c812

Added DST to signature and removed unwraps.

ae1b4a5

Added conversion function for scalar from BLS12 to Jubjub.

c8c5556

Added wip to and from bytes for Schnorr signing key.

a7ed87e

Added comments and derive for main structs.

56fba1e

Added eval_dense_mapping function to signature.

029be7a

Took comment into account and started to add signature comment descri…

78dedef

…ption.

Added description for Schnorr sign and verify.

89786bf

Added to and from bytes for verification key and signature.

64d50e1

Changing the variables name and the dependency depending on the futur…

9bfac40

…e_snark feature.

Added utils module for utility functions.

ab19eef

Small modifications based on JP feedback.

9f912ba

Modifications according to reviews.

1080152

Finished changing variables name.

9ec3f5d

Added crates for jubjub and poseidon to try to replace midnight while…

0c97400

… it is not published.

Change to dusk jubjub dependency.

3ddf71f

damrobi force-pushed the damrobi/stm-add-schnorr-sig-module branch from 00276b3 to 3ddf71f Compare November 17, 2025 11:40

damrobi temporarily deployed to testing-preview November 17, 2025 11:52 — with GitHub Actions Inactive

damrobi added 2 commits November 18, 2025 11:06

Modify last variable names and removed evaluate_dense_mapping functio…

23aa825

…n from schnorr signature.

fmt and clippy.

cf1b5dc

curiecrypt reviewed Nov 19, 2025

View reviewed changes

Correction on variable names and started adding bench for schnorr_sig…

40c68d6

…nature.

damrobi had a problem deploying to testing-preview November 19, 2025 15:33 — with GitHub Actions Failure

Implementation of Schnorr signature module for mithril-stm. #2761

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Implementation of Schnorr signature module for mithril-stm. #2761

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damrobi commented Nov 3, 2025

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