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hmac.py
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"""HMAC (Keyed-Hashing for Message Authentication) Python module. Implements the HMAC algorithm as described by RFC 2104. """ import warnings as _warnings from _operator import _compare_digest as compare_digest import hashlib as _hashlib import _hashlib as _hashlibopenssl import _hmacopenssl 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 class HMAC: """RFC 2104 HMAC class. Also complies with RFC 4231. 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. *OR* A hash name suitable for hashlib.new(). Defaults to hashlib.md5. Implicit default to hashlib.md5 is deprecated and will be removed in Python 3.6. Note: key and msg must be a bytes or bytearray objects. """ if _hashlibopenssl.get_fips_mode(): raise ValueError( 'This class is not available in FIPS mode. ' + 'Use hmac.new().' ) if not isinstance(key, (bytes, bytearray)): raise TypeError("key: expected bytes or bytearray, but got %r" % type(key).__name__) if digestmod is None: _warnings.warn("HMAC() without an explicit digestmod argument " "is deprecated.", PendingDeprecationWarning, 2) digestmod = _hashlib.md5 if callable(digestmod): self.digest_cons = digestmod elif isinstance(digestmod, str): self.digest_cons = lambda d=b'': _hashlib.new(digestmod, d) 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 if hasattr(self.inner, 'block_size'): blocksize = self.inner.block_size if blocksize < 16: _warnings.warn('block_size of %d seems too small; using our ' 'default of %d.' % (blocksize, self.blocksize), RuntimeWarning, 2) blocksize = self.blocksize else: _warnings.warn('No block_size attribute on given digest object; ' 'Assuming %d.' % (self.blocksize), RuntimeWarning, 2) blocksize = self.blocksize # self.blocksize is the default blocksize. self.block_size is # effective block size as well as the public API attribute. self.block_size = blocksize if len(key) > blocksize: key = self.digest_cons(key).digest() key = key.ljust(blocksize, b'\0') self.outer.update(key.translate(trans_5C)) self.inner.update(key.translate(trans_36)) if msg is not None: self.update(msg) @property def name(self): return "hmac-" + self.inner.name def update(self, msg): """Update this hashing object with the string msg. """ if _hashlibopenssl.get_fips_mode(): raise ValueError('hmac.HMAC is not available in FIPS mode') 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. """ # Call __new__ directly to avoid the expensive __init__. other = self.__class__.__new__(self.__class__) 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 _get_openssl_name(digestmod): if digestmod is None: raise ValueError("'digestmod' argument is mandatory in FIPS mode") if isinstance(digestmod, str): return digestmod.lower() elif callable(digestmod): digestmod = digestmod(b'') if not isinstance(digestmod, _hashlibopenssl.HASH): raise TypeError( 'Only OpenSSL hashlib hashes are accepted in FIPS mode.') return digestmod.name.lower().replace('_', '-') class HMAC_openssl(_hmacopenssl.HMAC): def __new__(cls, key, msg = None, digestmod = None): if not isinstance(key, (bytes, bytearray)): raise TypeError("key: expected bytes or bytearray, but got %r" % type(key).__name__) name = _get_openssl_name(digestmod) result = _hmacopenssl.HMAC.__new__(cls, key, digestmod=name) if msg: result.update(msg) return result if _hashlibopenssl.get_fips_mode(): HMAC = HMAC_openssl 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)