Computing Skein hashes

The interface for hashing with Skein is conveniently similar to the hashlib module of Python’s standard library. A new hash object is created by one of the following three functions:

skein.skein256(init=b"", digest_bits=256, mac=b"")

skein.skein512(init=b"", digest_bits=512, mac=b"")

skein.skein1024(init=b"", digest_bits=1024, mac=b"")

These constructor functions return a corresponding hash object for Skein-256, Skein-512, or Skein-1024 (i.e. 256, 512, or 1024 bits internal state). They optionally take an initial chunk of data to hash, the desired digest length in bits (must be a multiple of 8), and a message authentication code to hash into the digest (as defined in the Skein specification).

A hash object has the following methods:

update(data)

Hash the given chunk of (bytes) data into the internal state. (String data has to be encoded to bytes first.) Repeated calls are equivalent to a single call with the concatenation of all the arguments.

digest()

Return the digest of all data processed so far. This is a bytes object of length digest_size.

hexdigest()

Like digest(), but returning the digest as a string of hexadecimal digits.

copy()

Return a clone of the hash object, e.g. to efficiently compute hashes of data sharing a common prefix.

In addition each hash object has the following attributes:

name

Name of the algorithm, i.e. "Skein-256", "Skein-512", or "Skein-1024".

block_bits

Internal state size in bits, i.e. 256, 512, or 1024.

block_size

Internal state size in bytes (conforming to hashlib), i.e. 32, 64, or 128.

digest_bits

Output digest length in bits, i.e. the value given to the constructor function (or default).

digest_size

Digest size in bytes.

Examples

Make a Skein-512 hash object with default digest length (512 bits) and hash some data:

>>> from skein import skein256, skein512, skein1024
>>> h = skein512()
>>> h.update(b"Nobody inspects")
>>> h.update(b" the spammish repetition")
>>> h.digest()
b'r\xac\xe9\xb5R\xc8\x82b\x1d[\xfa\xe1*/\x86\x91\xa4\xf1Wk\xb4~3\xf3B\xc3\xc0\x1dV\x94>\x00\xd3\xdb\x7f\xed1\xe3#\xc1\x00a^\xc2\x1d1\xdc?\xdb\x16`\xf7\xda\xcb1b5,\xa0\xf5W"\x1fX'
>>> h.digest_size, h.digest_bits
(64, 512)
>>> h.block_size, h.block_bits
(64, 512)

Similarly for Skein-1024-384:

>>> h = skein1024(b"Nobody inspects the spammish repetition", digest_bits=384)
>>> h.hexdigest()
'd97af1a979016051a38e00f53fa56e683d6c4796860c2819c4f3eb8d49a5e844216b7fdadbac636e95fd69b5f1b98427'
>>> h.digest_size, h.digest_bits
(48, 384)
>>> h.block_size, h.block_bits
(128, 1024)

Hashing with or without message authentication code (MAC):

>>> skein256(b"foo", mac=b"bar").hexdigest()
'267daea2fd2ff91611e7d6a162dd4927df549a4aaa2adfa78b49339a91f10bcb'
>>> skein256(b"foo").hexdigest()
'7c3181538a0b56933ae51e88d938308eaef834b6a27eaa7ea7e60efb2d83c700'