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.

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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
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- 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 23m 57s ⏱️ + 1m 1s
2 207 tests ±0 2 207 ✅ ±0 0 💤 ±0 0 ❌ ±0
6 887 runs ±0 6 887 ✅ ±0 0 💤 ±0 0 ❌ ±0

Results for commit cf446ba. ± Comparison against base commit 2ad7d5e.

♻️ This comment has been updated with latest results.

… one.

mithril-stm/src/schnorr_signature/signing_key.rs

…ons.

curiecrypt

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

curiecrypt · 2025-11-10T11:14:08Z

mithril-stm/Cargo.toml

 digest = { workspace = true }
+ff = "0.13.1"
+group = "0.13.0"
+midnight-circuits = { git = "https://github.com/midnightntwrk/midnight-zk", rev = "c88a50c2169f060120a52ad0980de90f08bc9535" }


I see that @kitounliu also used this revision. Don't we get the latest version of the midnight repo?
If that is not the case, can you write a comment for these revisions, giving the date of the rev and the reason for using this specific rev.

curiecrypt · 2025-11-10T11:52:09Z

mithril-stm/src/schnorr_signature/mod.rs

@@ -0,0 +1,168 @@
+#![allow(dead_code)]


Suggested change

#![allow(dead_code)]

/// TODO: Remove

#![allow(dead_code)]

curiecrypt · 2025-11-10T12:02:26Z

mithril-stm/src/schnorr_signature/mod.rs

+mod signing_key;
+mod verification_key;
+
+/// A DST to distinguish between use of Poseidon hash


Suggested change

/// A DST to distinguish between use of Poseidon hash

use signature::*;

use signing_key::*;

use verification_key::*;

/// A DST to distinguish between use of Poseidon hash

By doing so, we can simplify the imports in the files. In the future, we might make these uses public if needed.

curiecrypt · 2025-11-10T12:03:31Z

mithril-stm/src/schnorr_signature/signing_key.rs

+use crate::schnorr_signature::{
+    signature::SchnorrSignature, verification_key::SchnorrVerificationKey,
+};


Suggested change

use crate::schnorr_signature::{

signature::SchnorrSignature, verification_key::SchnorrVerificationKey,

};

use crate::schnorr_signature::{SchnorrSignature, SchnorrVerificationKey};

curiecrypt · 2025-11-10T12:10:08Z

mithril-stm/src/schnorr_signature/signing_key.rs

+        SchnorrSigningKey(JubjubScalar::random(rng))
+    }
+
+    // TODO: Check if we want the sign function to handle the randomness by itself


Let's explain the signature scheme in the function doc.

curiecrypt · 2025-11-10T12:11:06Z

mithril-stm/src/schnorr_signature/signing_key.rs

+        // Compute the random part of the signature with
+        // r1 = H(msg) * r
+        // r2 = g * r
+        let r = JubjubScalar::random(rng);


We should think of more descriptive variable names within the code. WDYT @jpraynaud ?

curiecrypt · 2025-11-10T12:12:09Z

mithril-stm/src/schnorr_signature/verification_key.rs

+    /// Convert a Shnorr secret key into a verification key
+    /// This is done by computing `vk = g * sk` where g is the generator
+    /// of the subgroup and sk is the schnorr secret key
+    fn from(sk: &SchnorrSigningKey) -> Self {


Similarly, we should use more descriptive names

curiecrypt · 2025-11-10T12:13:00Z

mithril-stm/src/schnorr_signature/signature.rs

+use crate::{
+    Index,
+    schnorr_signature::{
+        DST_LOTTERY, DST_SIGNATURE, JubjubHashToCurve, get_coordinates, hash_msg_to_jubjubbase,
+        jubjub_base_to_scalar, verification_key::SchnorrVerificationKey,
+    },
+};


Suggested change

use crate::{

Index,

schnorr_signature::{

DST_LOTTERY, DST_SIGNATURE, JubjubHashToCurve, get_coordinates, hash_msg_to_jubjubbase,

jubjub_base_to_scalar, verification_key::SchnorrVerificationKey,

},

};

use crate::{

Index,

schnorr_signature::{

DST_LOTTERY, DST_SIGNATURE, JubjubHashToCurve, SchnorrVerificationKey, get_coordinates,

hash_msg_to_jubjubbase, jubjub_base_to_scalar,

},

};

curiecrypt · 2025-11-10T12:13:24Z

mithril-stm/src/schnorr_signature/signature.rs

+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct SchnorrSignature {
+    pub(crate) sigma: JubjubSubgroup,
+    pub(crate) s: JubjubScalar,


Descriptive names : )

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

damrobi added 5 commits November 5, 2025 09:14

Added file structure for Schnorr signature module.

74d7030

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

c6bb7d6

Moved test out of proptest.

09ad452

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

2a992df

applied clippy.

1e07c07

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

View reviewed changes

damrobi added 3 commits November 5, 2025 09:49

Cargo.lock change.

7c929c1

Update msg to base field conversion.

f936f56

Add to and from bytes for SchnorrSignature.

bc9aa24

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

damrobi added 4 commits November 6, 2025 14:56

Removed prototype implementation of schnorr signature and started new…

bac5906

… one.

Added generate function for Schnorr signature.

5ef9fc0

Added conversion from sk to vk for use in signature.

8672cf2

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

660377c

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

View reviewed changes

damrobi added 6 commits November 6, 2025 16:53

Added sign function for SchnorrSigningKey and necessary helper functi…

da8c6f1

…ons.

Added test function for get_coordinates and fix the sign function.

f1bfa8b

Added verification function and tests to signature.

9195e0e

Removed unused dependency.

439344a

Added DST to signature and removed unwraps.

08552ea

Added conversion function for scalar from BLS12 to Jubjub.

3a84e72

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

damrobi added 2 commits November 7, 2025 15:01

Added wip to and from bytes for Schnorr signing key.

5400577

Added comments and derive for main structs.

fd1fb45

Added eval_dense_mapping function to signature.

cf446ba

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

curiecrypt reviewed Nov 10, 2025

View reviewed changes

-/// A DST to distinguish between use of Poseidon hash
+use signature::*;
+use signing_key::*;
+use verification_key::*;
+/// A DST to distinguish between use of Poseidon hash

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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github-actions bot commented Nov 5, 2025 •

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