Added internal python-only HMAC implementation
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Mark Qvist
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# This HMAC implementation comes directly from the HMAC implementation
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# included in Python 3.10.4, and is almost completely identical. It has
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# been modified to be a pure Python implementation, that is not dependent
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# on the system having OpenSSL binaries installed.
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import warnings as _warnings
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import hashlib as _hashlib
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trans_5C = bytes((x ^ 0x5C) for x in range(256))
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trans_36 = bytes((x ^ 0x36) for x in range(256))
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# The size of the digests returned by HMAC depends on the underlying
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# hashing module used. Use digest_size from the instance of HMAC instead.
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digest_size = None
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class HMAC:
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"""RFC 2104 HMAC class. Also complies with RFC 4231.
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This supports the API for Cryptographic Hash Functions (PEP 247).
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"""
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blocksize = 64 # 512-bit HMAC; can be changed in subclasses.
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__slots__ = (
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"_hmac", "_inner", "_outer", "block_size", "digest_size"
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)
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def __init__(self, key, msg=None, digestmod=''):
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"""Create a new HMAC object.
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key: bytes or buffer, key for the keyed hash object.
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msg: bytes or buffer, Initial input for the hash or None.
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digestmod: A hash name suitable for hashlib.new(). *OR*
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A hashlib constructor returning a new hash object. *OR*
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A module supporting PEP 247.
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Required as of 3.8, despite its position after the optional
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msg argument. Passing it as a keyword argument is
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recommended, though not required for legacy API reasons.
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"""
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if not isinstance(key, (bytes, bytearray)):
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raise TypeError("key: expected bytes or bytearray, but got %r" % type(key).__name__)
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if not digestmod:
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raise TypeError("Missing required parameter 'digestmod'.")
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self._hmac_init(key, msg, digestmod)
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def _hmac_init(self, key, msg, digestmod):
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if callable(digestmod):
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digest_cons = digestmod
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elif isinstance(digestmod, str):
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digest_cons = lambda d=b'': _hashlib.new(digestmod, d)
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else:
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digest_cons = lambda d=b'': digestmod.new(d)
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self._hmac = None
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self._outer = digest_cons()
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self._inner = digest_cons()
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self.digest_size = self._inner.digest_size
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if hasattr(self._inner, 'block_size'):
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blocksize = self._inner.block_size
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if blocksize < 16:
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_warnings.warn('block_size of %d seems too small; using our '
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'default of %d.' % (blocksize, self.blocksize),
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RuntimeWarning, 2)
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blocksize = self.blocksize
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else:
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_warnings.warn('No block_size attribute on given digest object; '
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'Assuming %d.' % (self.blocksize),
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RuntimeWarning, 2)
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blocksize = self.blocksize
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if len(key) > blocksize:
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key = digest_cons(key).digest()
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# self.blocksize is the default blocksize. self.block_size is
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# effective block size as well as the public API attribute.
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self.block_size = blocksize
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key = key.ljust(blocksize, b'\0')
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self._outer.update(key.translate(trans_5C))
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self._inner.update(key.translate(trans_36))
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if msg is not None:
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self.update(msg)
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@property
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def name(self):
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if self._hmac:
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return self._hmac.name
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else:
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return f"hmac-{self._inner.name}"
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def update(self, msg):
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"""Feed data from msg into this hashing object."""
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inst = self._hmac or self._inner
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inst.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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# Call __new__ directly to avoid the expensive __init__.
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other = self.__class__.__new__(self.__class__)
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other.digest_size = self.digest_size
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if self._hmac:
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other._hmac = self._hmac.copy()
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other._inner = other._outer = None
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else:
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other._hmac = None
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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 _current(self):
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"""Return a hash object for the current state.
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To be used only internally with digest() and hexdigest().
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"""
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if self._hmac:
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return self._hmac
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else:
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h = self._outer.copy()
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h.update(self._inner.digest())
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return h
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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 the hmac value as bytes. 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._current()
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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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h = self._current()
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return h.hexdigest()
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def new(key, msg=None, digestmod=''):
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"""Create a new hashing object and return it.
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key: bytes or buffer, The starting key for the hash.
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msg: bytes or buffer, Initial input for the hash, or None.
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digestmod: A hash name suitable for hashlib.new(). *OR*
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A hashlib constructor returning a new hash object. *OR*
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A module supporting PEP 247.
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Required as of 3.8, despite its position after the optional
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msg argument. Passing it as a keyword argument is
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recommended, though not required for legacy API reasons.
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You can now feed arbitrary bytes 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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or hexdigest() methods.
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"""
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return HMAC(key, msg, digestmod)
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def digest(key, msg, digest):
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"""Fast inline implementation of HMAC.
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key: bytes or buffer, The key for the keyed hash object.
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msg: bytes or buffer, Input message.
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digest: A hash name suitable for hashlib.new() for best performance. *OR*
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A hashlib constructor returning a new hash object. *OR*
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A module supporting PEP 247.
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"""
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if callable(digest):
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digest_cons = digest
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elif isinstance(digest, str):
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digest_cons = lambda d=b'': _hashlib.new(digest, d)
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else:
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digest_cons = lambda d=b'': digest.new(d)
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inner = digest_cons()
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outer = digest_cons()
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blocksize = getattr(inner, 'block_size', 64)
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if len(key) > blocksize:
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key = digest_cons(key).digest()
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key = key + b'\x00' * (blocksize - len(key))
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inner.update(key.translate(trans_36))
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outer.update(key.translate(trans_5C))
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inner.update(msg)
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outer.update(inner.digest())
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return outer.digest()
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