1 """HMAC (Keyed-Hashing for Message Authentication) Python module. 2 3 Implements the HMAC algorithm as described by RFC 2104. 4 """ 5 6 import warnings as _warnings 7 8 trans_5C = "".join ([chr (x ^ 0x5C) for x in xrange(256)]) 9 trans_36 = "".join ([chr (x ^ 0x36) for x in xrange(256)]) 10 11 # The size of the digests returned by HMAC depends on the underlying 12 # hashing module used. Use digest_size from the instance of HMAC instead. 13 digest_size = None 14 15 # A unique object passed by HMAC.copy() to the HMAC constructor, in order 16 # that the latter return very quickly. HMAC("") in contrast is quite 17 # expensive. 18 _secret_backdoor_key = [] 19 20 class HMAC: 21 """RFC 2104 HMAC class. Also complies with RFC 4231. 22 23 This supports the API for Cryptographic Hash Functions (PEP 247). 24 """ 25 blocksize = 64 # 512-bit HMAC; can be changed in subclasses. 26 27 def __init__(self, key, msg = None, digestmod = None): 28 """Create a new HMAC object. 29 30 key: key for the keyed hash object. 31 msg: Initial input for the hash, if provided. 32 digestmod: A module supporting PEP 247. *OR* 33 A hashlib constructor returning a new hash object. 34 Defaults to hashlib.md5. 35 """ 36 37 if key is _secret_backdoor_key: # cheap 38 return 39 40 if digestmod is None: 41 import hashlib 42 digestmod = hashlib.md5 43 44 if hasattr(digestmod, '__call__'): 45 self.digest_cons = digestmod 46 else: 47 self.digest_cons = lambda d='': digestmod.new(d) 48 49 self.outer = self.digest_cons() 50 self.inner = self.digest_cons() 51 self.digest_size = self.inner.digest_size 52 53 if hasattr(self.inner, 'block_size'): 54 blocksize = self.inner.block_size 55 if blocksize < 16: 56 # Very low blocksize, most likely a legacy value like 57 # Lib/sha.py and Lib/md5.py have. 58 _warnings.warn('block_size of %d seems too small; using our ' 59 'default of %d.' % (blocksize, self.blocksize), 60 RuntimeWarning, 2) 61 blocksize = self.blocksize 62 else: 63 _warnings.warn('No block_size attribute on given digest object; ' 64 'Assuming %d.' % (self.blocksize), 65 RuntimeWarning, 2) 66 blocksize = self.blocksize 67 68 if len(key) > blocksize: 69 key = self.digest_cons(key).digest() 70 71 key = key + chr(0) * (blocksize - len(key)) 72 self.outer.update(key.translate(trans_5C)) 73 self.inner.update(key.translate(trans_36)) 74 if msg is not None: 75 self.update(msg) 76 77 ## def clear(self): 78 ## raise NotImplementedError, "clear() method not available in HMAC." 79 80 def update(self, msg): 81 """Update this hashing object with the string msg. 82 """ 83 self.inner.update(msg) 84 85 def copy(self): 86 """Return a separate copy of this hashing object. 87 88 An update to this copy won't affect the original object. 89 """ 90 other = self.__class__(_secret_backdoor_key) 91 other.digest_cons = self.digest_cons 92 other.digest_size = self.digest_size 93 other.inner = self.inner.copy() 94 other.outer = self.outer.copy() 95 return other 96 97 def _current(self): 98 """Return a hash object for the current state. 99 100 To be used only internally with digest() and hexdigest(). 101 """ 102 h = self.outer.copy() 103 h.update(self.inner.digest()) 104 return h 105 106 def digest(self): 107 """Return the hash value of this hashing object. 108 109 This returns a string containing 8-bit data. The object is 110 not altered in any way by this function; you can continue 111 updating the object after calling this function. 112 """ 113 h = self._current() 114 return h.digest() 115 116 def hexdigest(self): 117 """Like digest(), but returns a string of hexadecimal digits instead. 118 """ 119 h = self._current() 120 return h.hexdigest() 121 122 def new(key, msg = None, digestmod = None): 123 """Create a new hashing object and return it. 124 125 key: The starting key for the hash. 126 msg: if available, will immediately be hashed into the object's starting 127 state. 128 129 You can now feed arbitrary strings into the object using its update() 130 method, and can ask for the hash value at any time by calling its digest() 131 method. 132 """ 133 return HMAC(key, msg, digestmod) 134
