Add domain separation parameter to hash_to_scalar#164
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Add a `domain: &[u8; 32]` parameter to `Scalar::hash_to_scalar` for domain separation. When the domain is all zeros, no prefix is applied — output is identical to the previous implementation. When non-zero, the 32-byte domain is prepended to the input before hashing. This is a compile-time breaking API change. All existing callers should initially pass `&[0u8; 32]` and adopt real domain tags incrementally.
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Pull request overview
This PR introduces explicit domain separation for Scalar::hash_to_scalar by adding a 32-byte domain parameter and conditionally prefixing it to the hash input, while preserving legacy behavior when the domain is all zeros.
Changes:
- Updated
Scalar::hash_to_scalarsignature tohash_to_scalar(domain: &[u8; 32], input: &[u8])and prependsdomainiff it’s non-zero. - Added tests to ensure the zero-domain path matches the legacy construction and updated existing fuzz property usage.
- Documented the breaking API change in
CHANGELOG.md.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
src/scalar/dusk.rs |
Adds the domain parameter + conditional prefixing logic; adds/updates tests for legacy compatibility and domain separation. |
CHANGELOG.md |
Notes the new domain parameter and the backward-compatible zero-domain behavior. |
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HDauven
approved these changes
Mar 20, 2026
Pin the exact scalar output for a known domain and input, ensuring any change to the hash construction is caught by the test suite.
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Add a
domain: &[u8; 32]parameter toScalar::hash_to_scalarfor domain separation. When the domain is all zeros, no prefix is applied — output is identical to the previous implementation. When non-zero, the 32-byte domain is prepended to the input before hashing.This is a compile-time breaking API change. All existing callers should initially pass
&[0u8; 32]and adopt real domain tags incrementally.