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1"""HMAC (Keyed-Hashing for Message Authentication) Python module.
2
3Implements the HMAC algorithm as described by RFC 2104.
4"""
5
6import warnings as _warnings
7
8from operator import _compare_digest as compare_digest
9
10
11trans_5C = "".join ([chr (x ^ 0x5C) for x in xrange(256)])
12trans_36 = "".join ([chr (x ^ 0x36) for x in xrange(256)])
13
14# The size of the digests returned by HMAC depends on the underlying
15# hashing module used.  Use digest_size from the instance of HMAC instead.
16digest_size = None
17
18# A unique object passed by HMAC.copy() to the HMAC constructor, in order
19# that the latter return very quickly.  HMAC("") in contrast is quite
20# expensive.
21_secret_backdoor_key = []
22
23class HMAC:
24    """RFC 2104 HMAC class.  Also complies with RFC 4231.
25
26    This supports the API for Cryptographic Hash Functions (PEP 247).
27    """
28    blocksize = 64  # 512-bit HMAC; can be changed in subclasses.
29
30    def __init__(self, key, msg = None, digestmod = None):
31        """Create a new HMAC object.
32
33        key:       key for the keyed hash object.
34        msg:       Initial input for the hash, if provided.
35        digestmod: A module supporting PEP 247.  *OR*
36                   A hashlib constructor returning a new hash object.
37                   Defaults to hashlib.md5.
38        """
39
40        if key is _secret_backdoor_key: # cheap
41            return
42
43        if digestmod is None:
44            import hashlib
45            digestmod = hashlib.md5
46
47        if hasattr(digestmod, '__call__'):
48            self.digest_cons = digestmod
49        else:
50            self.digest_cons = lambda d='': digestmod.new(d)
51
52        self.outer = self.digest_cons()
53        self.inner = self.digest_cons()
54        self.digest_size = self.inner.digest_size
55
56        if hasattr(self.inner, 'block_size'):
57            blocksize = self.inner.block_size
58            if blocksize < 16:
59                # Very low blocksize, most likely a legacy value like
60                # Lib/sha.py and Lib/md5.py have.
61                _warnings.warn('block_size of %d seems too small; using our '
62                               'default of %d.' % (blocksize, self.blocksize),
63                               RuntimeWarning, 2)
64                blocksize = self.blocksize
65        else:
66            _warnings.warn('No block_size attribute on given digest object; '
67                           'Assuming %d.' % (self.blocksize),
68                           RuntimeWarning, 2)
69            blocksize = self.blocksize
70
71        if len(key) > blocksize:
72            key = self.digest_cons(key).digest()
73
74        key = key + chr(0) * (blocksize - len(key))
75        self.outer.update(key.translate(trans_5C))
76        self.inner.update(key.translate(trans_36))
77        if msg is not None:
78            self.update(msg)
79
80##    def clear(self):
81##        raise NotImplementedError, "clear() method not available in HMAC."
82
83    def update(self, msg):
84        """Update this hashing object with the string msg.
85        """
86        self.inner.update(msg)
87
88    def copy(self):
89        """Return a separate copy of this hashing object.
90
91        An update to this copy won't affect the original object.
92        """
93        other = self.__class__(_secret_backdoor_key)
94        other.digest_cons = self.digest_cons
95        other.digest_size = self.digest_size
96        other.inner = self.inner.copy()
97        other.outer = self.outer.copy()
98        return other
99
100    def _current(self):
101        """Return a hash object for the current state.
102
103        To be used only internally with digest() and hexdigest().
104        """
105        h = self.outer.copy()
106        h.update(self.inner.digest())
107        return h
108
109    def digest(self):
110        """Return the hash value of this hashing object.
111
112        This returns a string containing 8-bit data.  The object is
113        not altered in any way by this function; you can continue
114        updating the object after calling this function.
115        """
116        h = self._current()
117        return h.digest()
118
119    def hexdigest(self):
120        """Like digest(), but returns a string of hexadecimal digits instead.
121        """
122        h = self._current()
123        return h.hexdigest()
124
125def new(key, msg = None, digestmod = None):
126    """Create a new hashing object and return it.
127
128    key: The starting key for the hash.
129    msg: if available, will immediately be hashed into the object's starting
130    state.
131
132    You can now feed arbitrary strings into the object using its update()
133    method, and can ask for the hash value at any time by calling its digest()
134    method.
135    """
136    return HMAC(key, msg, digestmod)
137