python-pskc branch master updated. 0.1-40-g1b9ee9f

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http://arthurdejong.org/git/python-pskc/commit/?id=1b9ee9f51496ccb10094f9d5844589948a887a08

commit 1b9ee9f51496ccb10094f9d5844589948a887a08
Author: Arthur de Jong <arthur@arthurdejong.org>
Date:   Sat Jun 14 23:40:45 2014 +0200

    Support PBKDF2 PRF argument
    
    Support specifying a pseudorandom function for PBKDF2 key derivation. It
    currently supports any HMAC that the MAC checking also supports.

diff --git a/pskc/encryption.py b/pskc/encryption.py
index 6b45a7b..a073314 100644
--- a/pskc/encryption.py
+++ b/pskc/encryption.py
@@ -117,7 +117,7 @@ class KeyDerivation(object):
       pbkdf2_salt: salt value
       pbkdf2_iterations: number of iterations to use
       pbkdf2_key_length: required key lengt
-      pbkdf2_prf: name of pseudorandom function used (HMAC-SHA1 is assumed)
+      pbkdf2_prf: name of pseudorandom function used
     """
 
     def __init__(self, key_deriviation=None):
@@ -158,13 +158,17 @@ class KeyDerivation(object):
             raise KeyDerivationError('No algorithm specified')
         if self.algorithm.endswith('#pbkdf2'):
             from Crypto.Protocol.KDF import PBKDF2
-            # TODO: support pseudorandom function (prf)
+            from pskc.mac import get_hmac
+            prf = None
             if self.pbkdf2_prf:
-                raise KeyDerivationError(
-                    'Pseudorandom function unsupported: %r' % self.pbkdf2_prf)
+                prf = get_hmac(self.pbkdf2_prf)
+                if prf is None:
+                    raise KeyDerivationError(
+                        'Pseudorandom function unsupported: %r' %
+                        self.pbkdf2_prf)
             return PBKDF2(
                 password, self.pbkdf2_salt, dkLen=self.pbkdf2_key_length,
-                count=self.pbkdf2_iterations, prf=None)
+                count=self.pbkdf2_iterations, prf=prf)
         else:
             raise KeyDerivationError(
                 'Unsupported algorithm: %r' % self.algorithm)

http://arthurdejong.org/git/python-pskc/commit/?id=79b9a7d99ab081f33a8c3e2028a275216482a54a

commit 79b9a7d99ab081f33a8c3e2028a275216482a54a
Author: Arthur de Jong <arthur@arthurdejong.org>
Date:   Sat Jun 14 23:35:50 2014 +0200

    Provide a get_hmac() function
    
    Refactor the functionality to find an HMAC function into a separate
    function.

diff --git a/pskc/mac.py b/pskc/mac.py
index 084d641..7e66d6e 100644
--- a/pskc/mac.py
+++ b/pskc/mac.py
@@ -29,16 +29,24 @@ with the PSKC encryption key.
 """
 
 
-import hashlib
-import hmac
 import re
 
-from pskc.encryption import EncryptedValue
-
 
 _hmac_url_re = re.compile(r'^.*#hmac-(?P<hash>[a-z0-9]+)$')
 
 
+def get_hmac(algorithm):
+    """Return an HMAC function that takes a secret and a value and returns a
+    digest."""
+    import hashlib
+    import hmac
+    match = _hmac_url_re.search(algorithm)
+    if match:
+        digestmod = getattr(hashlib, match.group('hash'), None)
+        if digestmod is not None:
+            return lambda key, value: hmac.new(key, value, digestmod).digest()
+
+
 class ValueMAC(object):
     """Provide MAC checking ability to PSKC data values."""
 
@@ -66,15 +74,11 @@ class ValueMAC(object):
         key = self.mac.key
         if key is None:
             raise DecryptionError('No MAC key available')
-        digestmod = None
-        match = _hmac_url_re.search(self.mac.algorithm)
-        if match:
-            digestmod = getattr(hashlib, match.group('hash'), None)
-        if digestmod is None:
+        hmacfn = get_hmac(self.mac.algorithm)
+        if hmacfn is None:
             raise DecryptionError(
                 'Unsupported MAC algorithm: %r' % self.mac.algorithm)
-        h = hmac.new(key, value, digestmod).digest()
-        if h != self._value_mac:
+        if hmacfn(key, value) != self._value_mac:
             raise DecryptionError('MAC value does not match')
         return True
 
@@ -89,6 +93,7 @@ class MAC(object):
     """
 
     def __init__(self, pskc, mac_method=None):
+        from pskc.encryption import EncryptedValue
         self.algorithm = None
         self._mac_key = EncryptedValue(pskc.encryption)
         self.parse(mac_method)

-----------------------------------------------------------------------

Summary of changes:
 pskc/encryption.py |   14 +++++++++-----
 pskc/mac.py        |   27 ++++++++++++++++-----------
 2 files changed, 25 insertions(+), 16 deletions(-)


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