108 lines
3.4 KiB
Python
108 lines
3.4 KiB
Python
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"""HMAC (Keyed-Hashing for Message Authentication) Python module.
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Implements the HMAC algorithm as described by RFC 2104.
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"""
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def _strxor(s1, s2):
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"""Utility method. XOR the two strings s1 and s2 (must have same length).
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"""
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return "".join(map(lambda x, y: chr(ord(x) ^ ord(y)), s1, s2))
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# The size of the digests returned by HMAC depends on the underlying
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# hashing module used.
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digest_size = None
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# A unique object passed by HMAC.copy() to the HMAC constructor, in order
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# that the latter return very quickly. HMAC("") in contrast is quite
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# expensive.
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_secret_backdoor_key = []
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class HMAC:
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"""RFC2104 HMAC class.
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This supports the API for Cryptographic Hash Functions (PEP 247).
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"""
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def __init__(self, key, msg = None, digestmod = None):
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"""Create a new HMAC object.
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key: key for the keyed hash object.
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msg: Initial input for the hash, if provided.
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digestmod: A module supporting PEP 247. Defaults to the md5 module.
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"""
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if key is _secret_backdoor_key: # cheap
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return
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if digestmod is None:
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import md5
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digestmod = md5
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self.digestmod = digestmod
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self.outer = digestmod.new()
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self.inner = digestmod.new()
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self.digest_size = digestmod.digest_size
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blocksize = 64
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ipad = "\x36" * blocksize
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opad = "\x5C" * blocksize
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if len(key) > blocksize:
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key = digestmod.new(key).digest()
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key = key + chr(0) * (blocksize - len(key))
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self.outer.update(_strxor(key, opad))
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self.inner.update(_strxor(key, ipad))
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if msg is not None:
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self.update(msg)
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## def clear(self):
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## raise NotImplementedError, "clear() method not available in HMAC."
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def update(self, msg):
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"""Update this hashing object with the string msg.
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"""
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self.inner.update(msg)
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def copy(self):
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"""Return a separate copy of this hashing object.
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An update to this copy won't affect the original object.
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"""
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other = HMAC(_secret_backdoor_key)
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other.digestmod = self.digestmod
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other.digest_size = self.digest_size
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other.inner = self.inner.copy()
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other.outer = self.outer.copy()
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return other
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def digest(self):
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"""Return the hash value of this hashing object.
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This returns a string containing 8-bit data. The object is
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not altered in any way by this function; you can continue
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updating the object after calling this function.
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"""
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h = self.outer.copy()
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h.update(self.inner.digest())
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return h.digest()
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def hexdigest(self):
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"""Like digest(), but returns a string of hexadecimal digits instead.
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"""
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return "".join([hex(ord(x))[2:].zfill(2)
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for x in tuple(self.digest())])
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def new(key, msg = None, digestmod = None):
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"""Create a new hashing object and return it.
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key: The starting key for the hash.
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msg: if available, will immediately be hashed into the object's starting
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state.
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You can now feed arbitrary strings into the object using its update()
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method, and can ask for the hash value at any time by calling its digest()
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method.
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"""
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return HMAC(key, msg, digestmod)
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