Added internal python-only HMAC implementation

RNS/Cryptography/HMAC.py

@@ -0,0 +1,183 @@
+# This HMAC implementation comes directly from the HMAC implementation
+# included in Python 3.10.4, and is almost completely identical. It has
+# been modified to be a pure Python implementation, that is not dependent
+# on the system having OpenSSL binaries installed.
+
+import warnings as _warnings
+import hashlib as _hashlib
+
+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.
+
+    __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("key: expected bytes or bytearray, but got %r" % type(key).__name__)
+
+        if not digestmod:
+            raise TypeError("Missing required parameter 'digestmod'.")
+
+        self._hmac_init(key, msg, digestmod)
+
+    def _hmac_init(self, key, msg, digestmod):
+        if callable(digestmod):
+            digest_cons = digestmod
+        elif isinstance(digestmod, str):
+            digest_cons = lambda d=b'': _hashlib.new(digestmod, d)
+        else:
+            digest_cons = lambda d=b'': digestmod.new(d)
+
+        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('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
+
+        if len(key) > blocksize:
+            key = digest_cons(key).digest()
+
+        # self.blocksize is the default blocksize. self.block_size is
+        # effective block size as well as the public API attribute.
+        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
+        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 callable(digest):
+        digest_cons = digest
+    elif isinstance(digest, str):
+        digest_cons = lambda d=b'': _hashlib.new(digest, d)
+    else:
+        digest_cons = lambda d=b'': digest.new(d)
+
+    inner = digest_cons()
+    outer = digest_cons()
+    blocksize = getattr(inner, 'block_size', 64)
+    if len(key) > blocksize:
+        key = digest_cons(key).digest()
+
+    key = key + b'\x00' * (blocksize - len(key))
+    inner.update(key.translate(trans_36))
+    outer.update(key.translate(trans_5C))
+    inner.update(msg)
+    outer.update(inner.digest())
+    return outer.digest()