Keccak hash functions defined in `Func` enum but not registered with implementations

keccak_224, keccak_256, keccak_384, and keccak_512 are defined in the Func IntEnum but have no corresponding hash implementation registered in FuncReg. Calling sum(data, "keccak-256") raises HashComputationError even though the function code is recognized.

Problem

In multihash/funcs.py, the Func enum includes Keccak variants:

class Func(IntEnum):
    keccak_224 = HASH_CODES["keccak-224"]  # 0x1A
    keccak_256 = HASH_CODES["keccak-256"]  # 0x1B
    keccak_384 = HASH_CODES["keccak-384"]  # 0x1C
    keccak_512 = HASH_CODES["keccak-512"]  # 0x1D

But neither _std_func_data nor _optional_func_data includes any Keccak entry. So:

from multihash import sum, Func

# This raises HashComputationError:
mh = sum(b"hello", Func.keccak_256)
# HashComputationError: no available hash function for Func.keccak_256

Go's implementation registers Keccak-256 and Keccak-512 via the register/sha3 package:

multihash.Register(multihash.KECCAK_256, sha3.NewLegacyKeccak256)
multihash.Register(multihash.KECCAK_512, sha3.NewLegacyKeccak512)

Proposed Solution

Add Keccak hash wrappers using pycryptodome or pysha3:

# In funcs.py, add to _optional_func_data:
try:
    from Crypto.Hash import keccak as _keccak_mod

    class Keccak256Hash:
        name = "keccak-256"
        digest_size = 32
        block_size = 136
        def __init__(self):
            self._hasher = _keccak_mod.new(digest_bits=256)
        def update(self, data): self._hasher.update(data)
        def digest(self): return self._hasher.digest()
        def hexdigest(self): return self._hasher.hexdigest()
        def copy(self):
            c = Keccak256Hash()
            c._hasher = self._hasher.copy()
            return c

    # Similar for Keccak224, Keccak384, Keccak512
    _optional_func_data.extend([
        (Func.keccak_224, "keccak-224", Keccak224Hash),
        (Func.keccak_256, "keccak-256", Keccak256Hash),
        (Func.keccak_384, "keccak-384", Keccak384Hash),
        (Func.keccak_512, "keccak-512", Keccak512Hash),
    ])
except ImportError:
    pass  # pycryptodome not available

Alternatively, use pysha3 or safe-pysha3 which provide sha3.keccak_256() etc.

Add pycryptodome (or pysha3) as an optional dependency in pyproject.toml.

Add tests verifying Keccak output matches known test vectors.

Related

• Go implementation: go-multihash register/sha3/multihash_sha3.go
• Test vectors: go-multihash sum_test.go includes Keccak-256 and Keccak-512 test cases

Start in multihash/funcs.py by examining Func, _std_func_data, and _optional_func_data, then check pyproject.toml for optional dependency conventions. Register the four Keccak variants with an available implementation and add tests comparing their digests with the referenced known vectors; done means sum() works for each function when the optional dependency is installed.