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+#
+#  KDF.py : a collection of Key Derivation Functions
+#
+# Part of the Python Cryptography Toolkit
+#
+# ===================================================================
+# The contents of this file are dedicated to the public domain.  To
+# the extent that dedication to the public domain is not available,
+# everyone is granted a worldwide, perpetual, royalty-free,
+# non-exclusive license to exercise all rights associated with the
+# contents of this file for any purpose whatsoever.
+# No rights are reserved.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+# ===================================================================
+
+"""This file contains a collection of standard key derivation functions.
+
+A key derivation function derives one or more secondary secret keys from
+one primary secret (a master key or a pass phrase).
+
+This is typically done to insulate the secondary keys from each other,
+to avoid that leakage of a secondary key compromises the security of the
+master key, or to thwart attacks on pass phrases (e.g. via rainbow tables).
+
+:undocumented: __revision__
+"""
+
+__revision__ = "$Id$"
+
+import math
+import struct
+
+from Crypto.Util.py3compat import *
+from Crypto.Hash import SHA as SHA1, HMAC
+from Crypto.Util.strxor import strxor
+
+def PBKDF1(password, salt, dkLen, count=1000, hashAlgo=None):
+    """Derive one key from a password (or passphrase).
+
+    This function performs key derivation according an old version of
+    the PKCS#5 standard (v1.5).
+    
+    This algorithm is called ``PBKDF1``. Even though it is still described
+    in the latest version of the PKCS#5 standard (version 2, or RFC2898),
+    newer applications should use the more secure and versatile `PBKDF2` instead.
+
+    :Parameters:
+     password : string
+        The secret password or pass phrase to generate the key from.
+     salt : byte string
+        An 8 byte string to use for better protection from dictionary attacks.
+        This value does not need to be kept secret, but it should be randomly
+        chosen for each derivation.
+     dkLen : integer
+        The length of the desired key. Default is 16 bytes, suitable for instance for `Crypto.Cipher.AES`.
+     count : integer
+        The number of iterations to carry out. It's recommended to use at least 1000.
+     hashAlgo : module
+        The hash algorithm to use, as a module or an object from the `Crypto.Hash` package.
+        The digest length must be no shorter than ``dkLen``.
+        The default algorithm is `SHA1`.
+
+    :Return: A byte string of length `dkLen` that can be used as key.
+    """
+    if not hashAlgo:
+        hashAlgo = SHA1
+    password = tobytes(password)
+    pHash = hashAlgo.new(password+salt)
+    digest = pHash.digest_size
+    if dkLen>digest:
+        raise ValueError("Selected hash algorithm has a too short digest (%d bytes)." % digest)
+    if len(salt)!=8:
+        raise ValueError("Salt is not 8 bytes long.")
+    for i in range(count-1):
+        pHash = pHash.new(pHash.digest())
+    return pHash.digest()[:dkLen]
+
+def PBKDF2(password, salt, dkLen=16, count=1000, prf=None):
+    """Derive one or more keys from a password (or passphrase).
+
+    This performs key derivation according to the PKCS#5 standard (v2.0),
+    by means of the ``PBKDF2`` algorithm.
+
+    :Parameters:
+     password : string
+        The secret password or pass phrase to generate the key from.
+     salt : string
+        A string to use for better protection from dictionary attacks.
+        This value does not need to be kept secret, but it should be randomly
+        chosen for each derivation. It is recommended to be at least 8 bytes long.
+     dkLen : integer
+        The cumulative length of the desired keys. Default is 16 bytes, suitable for instance for `Crypto.Cipher.AES`.
+     count : integer
+        The number of iterations to carry out. It's recommended to use at least 1000.
+     prf : callable
+        A pseudorandom function. It must be a function that returns a pseudorandom string
+        from two parameters: a secret and a salt. If not specified, HMAC-SHA1 is used.
+
+    :Return: A byte string of length `dkLen` that can be used as key material.
+        If you wanted multiple keys, just break up this string into segments of the desired length.
+"""
+    password = tobytes(password)
+    if prf is None:
+        prf = lambda p,s: HMAC.new(p,s,SHA1).digest()
+    key = b('')
+    i = 1
+    while len(key)<dkLen:
+        U = previousU = prf(password,salt+struct.pack(">I", i))
+        for j in range(count-1):
+            previousU = t = prf(password,previousU)
+            U = strxor(U,t)
+        key += U
+        i = i + 1
+    return key[:dkLen]
+