def test_split_as_chunks_and_recombine():
bytestring = get_random_bytes(100)
chunks = split_as_chunks(bytestring, chunk_size=25, must_pad=True)
assert all(len(x) == 25 for x in chunks)
result = recombine_chunks(chunks, chunk_size=25, must_unpad=True)
assert result == bytestring
chunks = split_as_chunks(bytestring, chunk_size=22, must_pad=True)
assert all(len(x) == 22 for x in chunks)
result = recombine_chunks(chunks, chunk_size=22, must_unpad=True)
assert result == bytestring
chunks = split_as_chunks(bytestring, chunk_size=25, must_pad=False)
assert all(len(x) == 25 for x in chunks)
result = recombine_chunks(chunks, chunk_size=25, must_unpad=False)
assert result == bytestring
with pytest.raises(ValueError, match="size multiple of chunk_size"):
split_as_chunks(bytestring, chunk_size=22, must_pad=False)
chunks = split_as_chunks(
bytestring, chunk_size=22, must_pad=False, accept_incomplete_chunk=True
)
assert not all(len(x) == 22 for x in chunks)
result = recombine_chunks(chunks, chunk_size=22, must_unpad=False)
assert result == bytestring
def recombine_secret_from_samir_shares(shares: list) -> bytes:
"""Permits to reconstruct a key which has its secret shared
into `shares_count` shares thanks to a list of `shares`
:param shares: list of k full-length shares (k being exactly the threshold of this shared secret)
:return: the key reconstructed as bytes"""
shares_per_secret = [] # List of lists of same-index 16-bytes shares
assert len(set(share[0] for share in shares)) == len(
shares) # All shares have unique idx
for share in shares:
idx, secret = share
chunks = split_as_chunks(secret, chunk_size=16, must_pad=False)
shares_per_secret.append([(idx, chunk) for chunk in chunks])
assert (len(set(len(chunks) for chunks in shares_per_secret)) == 1
) # Same-length lists
all_chunk_shares = list(zip(*shares_per_secret))
chunks = []
for chunk_shares in all_chunk_shares:
chunk = _recombine_128b_shares_into_bytestring(chunk_shares)
chunks.append(chunk)
secret = recombine_chunks(chunks,
chunk_size=SHAMIR_CHUNK_LENGTH,
must_unpad=True)
return secret