third_party/tlslite/tlslite/utils/hmac.py

   1 """HMAC (Keyed-Hashing for Message Authentication) Python module.
   2
   3 Implements the HMAC algorithm as described by RFC 2104.
   4
   5 (This file is modified from the standard library version to do faster
   6 copying)
   7 """
   8
   9 def _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.
  16 digest_size = None
  17
  18 class 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
  93 def 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)