precompile(secp256r1): align RIP-7212 with EIP-7951 specification

[doocho]

Description

Overview

This PR adds explicit infinity point validation to the secp256r1 precompile to comply with EIP-7951: Precompile for secp256r1 Curve Support specification.

Key Change

Added Infinity Point Check

// EIP-7951: Reject infinity point (0,0) encoding
if pk.iter().all(|b| *b == 0) {
    return None;
}

This prevents consensus failures from infinity point attacks by explicitly rejecting the point-at-infinity encoding.

EIP-7951 Compliance

The implementation satisfies EIP-7951 requirements through:

1. Precompile Address

• Address: 0x100 (256) - P256VERIFY_ADDRESS = 256

2. Gas Costs

• Osaka spec: 6900 gas (P256VERIFY_BASE_GAS_FEE_OSAKA)
• Legacy spec: 3450 gas (maintains L2 compatibility)

3. Input Validation (via p256 library)

• Signature bounds: 0 < r < n, 0 < s < n (enforced by Signature::from_slice)
• Public key bounds: 0 ≤ qx < p, 0 ≤ qy < p (enforced by VerifyingKey::from_encoded_point)
• Curve equation: qy² ≡ qx³ + ax + b (mod p) (enforced by VerifyingKey::from_encoded_point)
• Input length: exactly 160 bytes (enforced by input.len() != 160)

4. Modular Comparison

• ECDSA standard: r' ≡ r (mod n) (handled by p256 library's verify_prehash)

5. Failure Handling

• Returns empty bytes on failure
• Consumes same gas as successful verification

Testing

Added Test Cases

• ✅ Infinity point encoding rejection
• ✅ r = 0 and s = 0 rejection
• ✅ r ≥ n and s ≥ n rejection
• ✅ qx ≥ p and qy ≥ p rejection
• ✅ Osaka path 6900 gas verification
• ✅ OutOfGas error handling

Compatibility

• RIP-7212 compatibility: Existing valid signatures continue to work
• L2 compatibility: 3450 gas path maintained
• Interface: Same ABI, same calling convention

References

• EIP-7951: Precompile for secp256r1 Curve Support
• RIP-7212: secp256r1 precompile
• go-ethereum: PR #31991 (merged July 7, 2025)

[codspeed-hq]

CodSpeed Performance Report

Merging #3012 will not alter performance

_{Comparing doocho:feat/eip-7951-secp256r1 (881955b) with main (0e05a30)}

Summary

✅ 173 untouched