Issue #19254: Provide an optimized Python implementation of PBKDF2_HMAC

1 files changed, 63 insertions, 6 deletions

diff --git a/Lib/hashlib.py b/Lib/hashlib.py
index 73882d1872b..56a9360eac6 100644
--- a/Lib/hashlib.py
+++ b/Lib/hashlib.py
@@ -1,4 +1,4 @@
-#  Copyright (C) 2005-2010   Gregory P. Smith (greg@krypto.org)
+#.  Copyright (C) 2005-2010   Gregory P. Smith (greg@krypto.org)
 #  Licensed to PSF under a Contributor Agreement.
 #
 
@@ -61,7 +61,7 @@ algorithms_guaranteed = set(__always_supported)
 algorithms_available = set(__always_supported)
 
 __all__ = __always_supported + ('new', 'algorithms_guaranteed',
-                                'algorithms_available')
+                                'algorithms_available', 'pbkdf2_hmac')
 
 
 def __get_builtin_constructor(name):
@@ -147,13 +147,70 @@ except ImportError:
     new = __py_new
     __get_hash = __get_builtin_constructor
 
-# PBKDF2 requires OpenSSL 1.0+ with HMAC and SHA
 try:
+    # OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA
     from _hashlib import pbkdf2_hmac
 except ImportError:
-    pass
-else:
-    __all__ += ('pbkdf2_hmac',)
+    _trans_5C = bytes((x ^ 0x5C) for x in range(256))
+    _trans_36 = bytes((x ^ 0x36) for x in range(256))
+
+    def pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None):
+        """Password based key derivation function 2 (PKCS #5 v2.0)
+
+        This Python implementations based on the hmac module about as fast
+        as OpenSSL's PKCS5_PBKDF2_HMAC for short passwords and much faster
+        for long passwords.
+        """
+        if not isinstance(hash_name, str):
+            raise TypeError(hash_name)
+
+        if not isinstance(password, (bytes, bytearray)):
+            password = bytes(memoryview(password))
+        if not isinstance(salt, (bytes, bytearray)):
+            salt = bytes(memoryview(salt))
+
+        # Fast inline HMAC implementation
+        inner = new(hash_name)
+        outer = new(hash_name)
+        blocksize = getattr(inner, 'block_size', 64)
+        if len(password) > blocksize:
+            password = new(hash_name, password).digest()
+        password = password + b'\x00' * (blocksize - len(password))
+        inner.update(password.translate(_trans_36))
+        outer.update(password.translate(_trans_5C))
+
+        def prf(msg, inner=inner, outer=outer):
+            # PBKDF2_HMAC uses the password as key. We can re-use the same
+            # digest objects and and just update copies to skip initialization.
+            icpy = inner.copy()
+            ocpy = outer.copy()
+            icpy.update(msg)
+            ocpy.update(icpy.digest())
+            return ocpy.digest()
+
+        if iterations < 1:
+            raise ValueError(iterations)
+        if dklen is None:
+            dklen = outer.digest_size
+        if dklen < 1:
+            raise ValueError(dklen)
+
+        dkey = b''
+        loop = 1
+        from_bytes = int.from_bytes
+        while len(dkey) < dklen:
+            prev = prf(salt + loop.to_bytes(4, 'big'))
+            # endianess doesn't matter here as long to / from use the same
+            rkey = int.from_bytes(prev, 'big')
+            for i in range(iterations - 1):
+                prev = prf(prev)
+                # rkey = rkey ^ prev
+                rkey ^= from_bytes(prev, 'big')
+            loop += 1
+            dkey += rkey.to_bytes(inner.digest_size, 'big')
+
+        return dkey[:dklen]
+
 
 for __func_name in __always_supported:
     # try them all, some may not work due to the OpenSSL