fix: add canonical checks for fr/fq in U256Codec::deserialize_from_fields#21811
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iakovenkos merged 1 commit intomerge-train/barretenbergfrom Mar 20, 2026
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…elds Reject non-canonical field elements (>= modulus) in the Keccak transcript path to prevent Fiat-Shamir challenge grinding. A malicious prover could submit v+p instead of v, producing different Keccak hashes but identical algebraic values. Matches existing behavior of FrCodec (BB_ASSERT_LT) and the Solidity verifier (require(v < MODULUS)). Closes AztecProtocol/barretenberg-claude#452
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Summary
Reject non-canonical field elements (>= modulus) in
U256Codec::deserialize_from_fields.bb::fr/fqdeserialization fromuint32_t/uint64_t/uint256_tto addBB_ASSERT_LTcanonical checksFrCodecand the Solidity verifier (require(v < MODULUS))