| """HMAC (Keyed-Hashing for Message Authentication) Python module. |
| |
| Implements the HMAC algorithm as described by RFC 2104. |
| """ |
| |
| trans_5C = bytes((x ^ 0x5C) for x in range(256)) |
| trans_36 = bytes((x ^ 0x36) for x in range(256)) |
| |
| # The size of the digests returned by HMAC depends on the underlying |
| # hashing module used. Use digest_size from the instance of HMAC instead. |
| digest_size = None |
| |
| # A unique object passed by HMAC.copy() to the HMAC constructor, in order |
| # that the latter return very quickly. HMAC("") in contrast is quite |
| # expensive. |
| _secret_backdoor_key = [] |
| |
| class HMAC: |
| """RFC2104 HMAC class. |
| |
| This supports the API for Cryptographic Hash Functions (PEP 247). |
| """ |
| blocksize = 64 # 512-bit HMAC; can be changed in subclasses. |
| |
| def __init__(self, key, msg = None, digestmod = None): |
| """Create a new HMAC object. |
| |
| key: key for the keyed hash object. |
| msg: Initial input for the hash, if provided. |
| digestmod: A module supporting PEP 247. *OR* |
| A hashlib constructor returning a new hash object. |
| Defaults to hashlib.md5. |
| |
| Note: key and msg must be bytes objects. |
| """ |
| |
| if key is _secret_backdoor_key: # cheap |
| return |
| |
| if not isinstance(key, bytes): |
| if hasattr(key, "__index__"): |
| raise TypeError("key can't be a number") |
| key = bytes(key) |
| |
| if digestmod is None: |
| import hashlib |
| digestmod = hashlib.md5 |
| |
| if hasattr(digestmod, '__call__'): |
| self.digest_cons = digestmod |
| else: |
| self.digest_cons = lambda d=b'': digestmod.new(d) |
| |
| self.outer = self.digest_cons() |
| self.inner = self.digest_cons() |
| self.digest_size = self.inner.digest_size |
| |
| blocksize = self.blocksize |
| if len(key) > blocksize: |
| key = self.digest_cons(key).digest() |
| |
| key = key + bytes(blocksize - len(key)) |
| self.outer.update(key.translate(trans_5C)) |
| self.inner.update(key.translate(trans_36)) |
| if msg is not None: |
| self.update(msg) |
| |
| ## def clear(self): |
| ## raise NotImplementedError, "clear() method not available in HMAC." |
| |
| def update(self, msg): |
| """Update this hashing object with the string msg. |
| """ |
| if not isinstance(msg, bytes): |
| if hasattr(msg, "__index__"): |
| raise TypeError("msg can't be a number") |
| msg = bytes(msg) |
| self.inner.update(msg) |
| |
| def copy(self): |
| """Return a separate copy of this hashing object. |
| |
| An update to this copy won't affect the original object. |
| """ |
| other = self.__class__(_secret_backdoor_key) |
| other.digest_cons = self.digest_cons |
| other.digest_size = self.digest_size |
| other.inner = self.inner.copy() |
| other.outer = self.outer.copy() |
| return other |
| |
| def _current(self): |
| """Return a hash object for the current state. |
| |
| To be used only internally with digest() and hexdigest(). |
| """ |
| h = self.outer.copy() |
| h.update(self.inner.digest()) |
| return h |
| |
| def digest(self): |
| """Return the hash value of this hashing object. |
| |
| This returns a string containing 8-bit data. The object is |
| not altered in any way by this function; you can continue |
| updating the object after calling this function. |
| """ |
| h = self._current() |
| return h.digest() |
| |
| def hexdigest(self): |
| """Like digest(), but returns a string of hexadecimal digits instead. |
| """ |
| h = self._current() |
| return h.hexdigest() |
| |
| def new(key, msg = None, digestmod = None): |
| """Create a new hashing object and return it. |
| |
| key: The starting key for the hash. |
| msg: if available, will immediately be hashed into the object's starting |
| state. |
| |
| You can now feed arbitrary strings into the object using its update() |
| method, and can ask for the hash value at any time by calling its digest() |
| method. |
| """ |
| return HMAC(key, msg, digestmod) |