feat(tests): add p256 precompile edge case test #2079
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Add two critical test cases for EIP-7951 p256verify precompile that commonly surface through fuzzing: 1. Near-field boundary modular reduction test - Tests values at P-1, P-2, N-1, N-2 boundaries - Exercises modular reduction edge cases - Catches off-by-one errors in field arithmetic - Tests carry propagation in multi-precision arithmetic 2. Scalar multiplication special bit pattern test - Tests edge cases with single high bit set (0x8000...) - Tests alternating bit patterns (0x5555...) - Exercises rarely-tested code paths in scalar multiplication - Can expose timing variations in implementations These tests complement existing Wycheproof vectors by focusing on implementation-specific arithmetic edge cases rather than purely cryptographic validity, making them valuable for catching subtle bugs in client implementations. 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>
spencer-tb
approved these changes
Aug 25, 2025
kevaundray
approved these changes
Aug 25, 2025
Thank you. Do you mind sharing the sage script you used if it's not sensitive? |
Still working on it but this is what I have so far! Going to merge your PR just now and add these extra points in a follow up :D |
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🗒️ Description
This PR adds an edge case test to the P256VERIFY precompile test suite that probes mathematical boundaries where implementations may fail.
Key addition:
near_field_boundary_p_minus_3): Tests the maximum valid X coordinate (P-3) withcorresponding edge values for signature components R=(N-2) and S=(N-1)/2. This ensures proper handling of field arithmetic at mathematical boundaries.
Why these tests matter:
These synthetic test vectors are designed to fail signature verification while passing all input validation, ensuring
implementations correctly handle extreme but mathematically valid inputs without overflow or consensus divergence.
🔗 Related Issues or PRs
✅ Checklist
toxchecks to avoid unnecessary CI fails:uvx --with=tox-uv tox -e lint,typecheck,spellcheck,markdownlinttest(osaka): add critical p256 precompile edge case testsAdditional validation performed: