hmac.py

"""HMAC (Keyed-Hashing for Message Authentication) module.

Implements the HMAC algorithm as described by RFC 2104.
"""

import hashlib as _hashlib

trans_5C = bytes((x ^ 0x5C) for x in range(256))
trans_36 = bytes((x ^ 0x36) for x in range(256))

# The size of the digests returned by HMAC depends on the underlying
# hashing module used.  Use digest_size from the instance of HMAC instead.
digest_size = None

def _translate(key, table):
    new_key = bytearray(len(key))
    for i in range(0, len(key)):
        new_key[i] = table[key[i]]
    return new_key

def digest(key, msg, digest):
    """Fast inline implementation of HMAC.

    key: bytes or buffer, The key for the keyed hash object.
    msg: bytes or buffer, Input message.
    digest: A hash name suitable for hashlib.new() for best performance. *OR*
            A hashlib constructor returning a new hash object. *OR*
            A module supporting PEP 247.
    """

    if callable(digest):
        digest_cons = digest
    elif isinstance(digest, str):
        digest_cons = lambda d=b'': _hashlib.new(digest, d)
    else:
        digest_cons = lambda d=b'': digest.new(d)

    inner = digest_cons()
    outer = digest_cons()
    blocksize = getattr(inner, 'block_size', 64)
    if len(key) > blocksize:
        key = digest_cons(key).digest()
    key = key + b'\x00' * (blocksize - len(key))

    inner.update(_translate(key,trans_36))
    outer.update(_translate(key,trans_5C))
    inner.update(msg)
    outer.update(inner.digest())
    return outer.digest()