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hmac.py
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"""HMAC (Keyed-Hashing for Message Authentication) module. Implements the HMAC algorithm as described by RFC 2104. """ try: import _hashlib as _hashopenssl except ImportError: _hashopenssl = None _functype = None from _operator import _compare_digest as compare_digest else: compare_digest = _hashopenssl.compare_digest _functype = type(_hashopenssl.openssl_sha256) # builtin type try: import _hmac except ImportError: _hmac = None 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 def _get_digest_constructor(digest_like): if callable(digest_like): return digest_like if isinstance(digest_like, str): def digest_wrapper(d=b''): import hashlib return hashlib.new(digest_like, d) else: def digest_wrapper(d=b''): return digest_like.new(d) return digest_wrapper class HMAC: """RFC 2104 HMAC class. Also complies with RFC 4231. This supports the API for Cryptographic Hash Functions (PEP 247). """ # Note: self.blocksize is the default blocksize; self.block_size # is effective block size as well as the public API attribute. blocksize = 64 # 512-bit HMAC; can be changed in subclasses. __slots__ = ( "_hmac", "_inner", "_outer", "block_size", "digest_size" ) def __init__(self, key, msg=None, digestmod=''): """Create a new HMAC object. key: bytes or buffer, key for the keyed hash object. msg: bytes or buffer, Initial input for the hash or None. digestmod: A hash name suitable for hashlib.new(). *OR* A hashlib constructor returning a new hash object. *OR* A module supporting PEP 247. Required as of 3.8, despite its position after the optional msg argument. Passing it as a keyword argument is recommended, though not required for legacy API reasons. """ if not isinstance(key, (bytes, bytearray)): raise TypeError(f"key: expected bytes or bytearray, " f"but got {type(key).__name__!r}") if not digestmod: raise TypeError("Missing required argument 'digestmod'.") self.__init(key, msg, digestmod) def __init(self, key, msg, digestmod): if _hashopenssl and isinstance(digestmod, (str, _functype)): try: self._init_openssl_hmac(key, msg, digestmod) return except _hashopenssl.UnsupportedDigestmodError: # pragma: no cover pass if _hmac and isinstance(digestmod, str): try: self._init_builtin_hmac(key, msg, digestmod) return except _hmac.UnknownHashError: # pragma: no cover pass self._init_old(key, msg, digestmod) def _init_openssl_hmac(self, key, msg, digestmod): self._hmac = _hashopenssl.hmac_new(key, msg, digestmod=digestmod) self._inner = self._outer = None # because the slots are defined self.digest_size = self._hmac.digest_size self.block_size = self._hmac.block_size _init_hmac = _init_openssl_hmac # for backward compatibility (if any) def _init_builtin_hmac(self, key, msg, digestmod): self._hmac = _hmac.new(key, msg, digestmod=digestmod) self._inner = self._outer = None # because the slots are defined self.digest_size = self._hmac.digest_size self.block_size = self._hmac.block_size def _init_old(self, key, msg, digestmod): import warnings digest_cons = _get_digest_constructor(digestmod) self._hmac = None self._outer = digest_cons() self._inner = 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(f"block_size of {blocksize} seems too small; " f"using our default of {self.blocksize}.", RuntimeWarning, 2) blocksize = self.blocksize # pragma: no cover else: warnings.warn("No block_size attribute on given digest object; " f"Assuming {self.blocksize}.", RuntimeWarning, 2) blocksize = self.blocksize # pragma: no cover if len(key) > blocksize: key = digest_cons(key).digest() self.block_size = blocksize 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): if self._hmac: return self._hmac.name else: return f"hmac-{self._inner.name}" def update(self, msg): """Feed data from msg into this hashing object.""" inst = self._hmac or self._inner inst.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_size = self.digest_size other.block_size = self.block_size if self._hmac: other._hmac = self._hmac.copy() other._inner = other._outer = None else: other._hmac = None 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(). """ if self._hmac: return self._hmac else: h = self._outer.copy() h.update(self._inner.digest()) return h def digest(self): """Return the hash value of this hashing object. This returns the hmac value as bytes. 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=''): """Create a new hashing object and return it. key: bytes or buffer, The starting key for the hash. msg: bytes or buffer, Initial input for the hash, or None. digestmod: A hash name suitable for hashlib.new(). *OR* A hashlib constructor returning a new hash object. *OR* A module supporting PEP 247. Required as of 3.8, despite its position after the optional msg argument. Passing it as a keyword argument is recommended, though not required for legacy API reasons. You can now feed arbitrary bytes into the object using its update() method, and can ask for the hash value at any time by calling its digest() or hexdigest() methods. """ return HMAC(key, msg, digestmod) def digest(key, msg, digest): """Fast inline implementation of HMAC. key: bytes or buffer, The key for the keyed hash object. msg: bytes or buffer, Input message. digest: A hash name suitable for hashlib.new() for best performance. *OR* A hashlib constructor returning a new hash object. *OR* A module supporting PEP 247. """ if _hashopenssl and isinstance(digest, (str, _functype)): try: return _hashopenssl.hmac_digest(key, msg, digest) except OverflowError: # OpenSSL's HMAC limits the size of the key to INT_MAX. # Instead of falling back to HACL* implementation which # may still not be supported due to a too large key, we # directly switch to the pure Python fallback instead # even if we could have used streaming HMAC for small keys # but large messages. return _compute_digest_fallback(key, msg, digest) except _hashopenssl.UnsupportedDigestmodError: pass if _hmac and isinstance(digest, str): try: return _hmac.compute_digest(key, msg, digest) except (OverflowError, _hmac.UnknownHashError): # HACL* HMAC limits the size of the key to UINT32_MAX # so we fallback to the pure Python implementation even # if streaming HMAC may have been used for small keys # and large messages. pass return _compute_digest_fallback(key, msg, digest) def _compute_digest_fallback(key, msg, digest): digest_cons = _get_digest_constructor(digest) inner = digest_cons() outer = digest_cons() blocksize = getattr(inner, 'block_size', 64) if len(key) > blocksize: key = digest_cons(key).digest() key = key.ljust(blocksize, b'\0') inner.update(key.translate(trans_36)) outer.update(key.translate(trans_5C)) inner.update(msg) outer.update(inner.digest()) return outer.digest()