/gdata/Crypto/Hash/HMAC.py

  1"""HMAC (Keyed-Hashing for Message Authentication) Python module.
  2
  3Implements the HMAC algorithm as described by RFC 2104.
  4
  5This is just a copy of the Python 2.2 HMAC module, modified to work when
  6used on versions of Python before 2.2.
  7"""
  8
  9__revision__ = "$Id: HMAC.py,v 1.5 2002/07/25 17:19:02 z3p Exp $"
 10
 11import string
 12
 13def _strxor(s1, s2):
 14    """Utility method. XOR the two strings s1 and s2 (must have same length).
 15    """
 16    return "".join(map(lambda x, y: chr(ord(x) ^ ord(y)), s1, s2))
 17
 18# The size of the digests returned by HMAC depends on the underlying
 19# hashing module used.
 20digest_size = None
 21
 22class HMAC:
 23    """RFC2104 HMAC class.
 24
 25    This supports the API for Cryptographic Hash Functions (PEP 247).
 26    """
 27
 28    def __init__(self, key, msg = None, digestmod = None):
 29        """Create a new HMAC object.
 30
 31        key:       key for the keyed hash object.
 32        msg:       Initial input for the hash, if provided.
 33        digestmod: A module supporting PEP 247. Defaults to the md5 module.
 34        """
 35        if digestmod == None:
 36            import md5
 37            digestmod = md5
 38
 39        self.digestmod = digestmod
 40        self.outer = digestmod.new()
 41        self.inner = digestmod.new()
 42        try:
 43            self.digest_size = digestmod.digest_size
 44        except AttributeError:
 45            self.digest_size = len(self.outer.digest())
 46
 47        blocksize = 64
 48        ipad = "\x36" * blocksize
 49        opad = "\x5C" * blocksize
 50
 51        if len(key) > blocksize:
 52            key = digestmod.new(key).digest()
 53
 54        key = key + chr(0) * (blocksize - len(key))
 55        self.outer.update(_strxor(key, opad))
 56        self.inner.update(_strxor(key, ipad))
 57        if (msg):
 58            self.update(msg)
 59
 60##    def clear(self):
 61##        raise NotImplementedError, "clear() method not available in HMAC."
 62
 63    def update(self, msg):
 64        """Update this hashing object with the string msg.
 65        """
 66        self.inner.update(msg)
 67
 68    def copy(self):
 69        """Return a separate copy of this hashing object.
 70
 71        An update to this copy won't affect the original object.
 72        """
 73        other = HMAC("")
 74        other.digestmod = self.digestmod
 75        other.inner = self.inner.copy()
 76        other.outer = self.outer.copy()
 77        return other
 78
 79    def digest(self):
 80        """Return the hash value of this hashing object.
 81
 82        This returns a string containing 8-bit data.  The object is
 83        not altered in any way by this function; you can continue
 84        updating the object after calling this function.
 85        """
 86        h = self.outer.copy()
 87        h.update(self.inner.digest())
 88        return h.digest()
 89
 90    def hexdigest(self):
 91        """Like digest(), but returns a string of hexadecimal digits instead.
 92        """
 93        return "".join([string.zfill(hex(ord(x))[2:], 2)
 94                        for x in tuple(self.digest())])
 95
 96def new(key, msg = None, digestmod = None):
 97    """Create a new hashing object and return it.
 98
 99    key: The starting key for the hash.
100    msg: if available, will immediately be hashed into the object's starting
101    state.
102
103    You can now feed arbitrary strings into the object using its update()
104    method, and can ask for the hash value at any time by calling its digest()
105    method.
106    """
107    return HMAC(key, msg, digestmod)
108