libcrux has an Incorrect Check of Signer Response Norm During Verification

The ML-DSA verification algorithm as specified in FIPS 204, subsection 6.3 requires verifiers to check that the infinity norm of the deserialized signer response $z$ does not exceed $\gamma_1 - \beta$ (line 13 of Algorithm 8). The same check is required to be performed during signature generation.

libcrux-ml-dsa did not perform this check correctly during signature verification, accepting signatures with signer response norm above the allowed maximum value. The check is correctly performed during signing.

Impact

Applications using libcrux-ml-dsa for signature verification would have accepted signatures that would be rejected by a conforming implementation.

Mitigation

Starting from version 0.0.8, signature verification uses the correct value for $\gamma_1$ in the signer response norm check.