Merge lp:~aj00200/anonplus/bug-901058 into lp:anonplus

[aj00200]

Fixed bug #901058 by making the OTP encryption use PyCryptos XOR function.

Fixed bug #901058 with the one-time-pad encryption. The encryption now uses PyCrypto's XOR rather than the addition and modulo devision method.

[aj00200 (aj00200)]

Crypto.Cipher.XOR should be used instead of Crypto.Util.strxor. Make sure to manage the pad length.

review: Needs Fixing

[lp:~aj00200/anonplus/bug-901058]

202. By aj00200 on 2012-02-10

Changed the PyCrypto XOR function to Crypto.Cipher.XOR. Also, raise an exception if the pad is over-used.

[aj00200 (aj00200)]

> Crypto.Cipher.XOR should be used instead of Crypto.Util.strxor. Make sure to
> manage the pad length.

The code has been updated to reflect this change.

review: Approve (security)

[al1ce (al1ce)]

Seems to be fine. :-)

review: Approve (security)

=== modified file 'src/libs/encryption/otp.py'
--- src/libs/encryption/otp.py	2011-10-23 15:41:09 +0000
+++ src/libs/encryption/otp.py	2012-02-10 02:36:20 +0000
@@ -3,42 +3,27 @@
 an attacker being able to know anything about the data other than its length.
 However, pad exchanges need to be done via a different encryption methods such
 as GPG encryption.'''
+from Crypto.Cipher import XOR
 import libs.encryption.base
 from libs.errors import UsageError
 
 class Encryption(libs.encryption.base.Encryption):
     '''One-time pad encryption class.'''
-    ord_range = 255 # Maximum value of the ord function
-
     def encrypt(self, data):
         '''Encrypt data using a one-time pad.'''
-        encrypted = ''
-        for character in data:
-            num = ord(character) + self.pad[-1]
-            num = num % self.ord_range
-            encrypted += str(num)
+        if self.pad_len < len(data):
+            raise Exception('The pad is to short for this data')
+
+        encrypted = self.pad.encrypt(data)
+        self.pad_len -= len(data)
+
         return encrypted
 
+    def decrypt(self, data):
+        '''Decrypt data using a one-time pad.'''
+        return self.encrypt(data)
+
     def set_pad(self, pad):
         '''Set the pad to given pad object.'''
-        if isinstance(pad, Pad):
-            self.pad = pad
-        else:
-            raise UsageError('The pad object must be an instance of Pad')
-
-class Pad(object):
-    '''Stores the current pad state and offers methods like pop()'''
-    def __init__(self, pad):
-        self.pad = pad
-
-    def __len__(self):
-        return len(self.pad)
-    
-    def pop(self):
-        '''Remove the last character from the pad and return it.
-        Yes, we are reading the pad backwards!
-        '''
-        last_char = self.pad[-1]
-        self.pad = self.pad[0:-1]
-        return last_char
-            
+        self.pad = XOR.new(pad)
+        self.pad_len = len(pad)