/gdata/tlslite/utils/hmac.py

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