Native Keccak Hashing for Signature Verification

Note: This is a legacy MPS that pre-dates the defined process; the components within may not conform to the MPS template.

Signature Verification - Native Keccak Hashing

This proposal implements and exposes the Keccak-256 hashing algorithm as an accessible function within a dedicated Compact cryptographic library.

Current cryptographic primitives available in Compact are not optimally suited for all use cases:

Ethereum Compatibility: The Ethereum ecosystem uses Keccak-256. Relying solely on different hash functions (like Poseidon/Griffin) or traditional ones (like SHA-256) complicates external verification and requires developers to implement inefficient conversion or custom logic.
Protocol Versatility: Exposing Keccak-256 offers a more diverse set of fundamental cryptographic tools, moving beyond reliance on traditional primitives like SHA-256.

The following function will be exposed within a dedicated Compact cryptographic library:

keccak256(data: Bytes<n>) → Bytes<32>

Behaviour:

Accepts arbitrary-length byte arrays as input.
Returns a fixed-length Bytes<32> output.
Output must be identical to standard Keccak-256 implementations across a range of test vectors.

User Story	Acceptance Criteria	Failure Scenarios
Compact API Exposure	The function `keccak256(data: Bytes<n>)` is exposed, accepting arbitrary-length byte arrays and returning a fixed-length `Bytes<32>` output.	Implementation results in a hash with a constraint count exceeding an acceptable threshold, making it economically non-viable for dApps.
Correct Hashing	The function output is identical to standard Keccak-256 implementations across a range of test vectors.	Mismatch between the off-circuit implementation and the in-circuit one.

Authoritative test vectors, the two best sources are:

Original Keccak KAT — the ShortMsgKAT_256.txt and ExtremelyLongMsgKAT_256.txt files from KeccakKAT-3.zip, available from keccak.noekeon.org. Uc These are the pre-NIST “pure Keccak” vectors that match Ethereum’s implementation.
Ethereum’s own test vectors — the js-ethereum-cryptography library maintained by the Ethereum Foundation has a dedicated Keccak-256 test vector file at ethereum/js-ethereum-cryptography on GitHub, which is the most directly relevant source for Ethereum compatibility testing.