Subversion Repositories Code-Repo

import math

substitution_map = {14:0,4:1,13:2,1:3,2:4,15:5,11:6,8:7,3:8,10:9,6:10,12:11,5:12,9:13,0:14,7:15}

key = [3,10,9,4,13,6,3,15]                              # Key
key_length = len(key) * 4                               # Calculate length of the key in bits
bytes_per_key = key_length / 8                  # Calculate the number of bytes for each round key (4 for a 32-bit key)
rounds = int(math.log(key_length,2))    # Calculate the number of rounds (5 for a 32-bit key)

ciphertext = [6,4,15,13]

def get_key(key, round):
        '''Returns the round key for the specified key.
        The round key is bytes_per_key bytes starting at the specified offset determined by round.'''
        round -= 1
        ret = []
        for index in range(bytes_per_key):
                ret.append(key[index + round])
        return ret

def xor_array(array, key):
        '''Xor the two arrays and returns the result.'''
        ret = []
        for index in range(len(array)):
                ret.append(array[index] ^ key[index])
        return ret

def sub_array(array):
        '''Runs the given array through the substitution map and returns the result.'''
        ret = []
        for index in range(len(array)):
                ret.append(substitution_map[array[index]])
        return ret

def perm_array(array):
        '''Permutes the given array and returns the results.'''
        ret = []
        for index in range(bytes_per_key-1,-1,-1):
                value = 0
                for entry in array:
                        value <<= 1
                        value |= (entry >> index) & 1
                ret.append(value)
        return ret

if __name__ == '__main__':
        working_array = ciphertext      # Initial array is the ciphertext
        print "Ciphertext:\t\t\t\t", ciphertext
        print

        # Print out the results for each step as it is calculated
        for round in range(rounds,1,-1):
                print "Round {0} Key:\t\t\t".format(round), get_key(key, round)
                working_array = xor_array(working_array, get_key(key, round))
                print "Round {0} U (xor'ed):\t\t".format(round),working_array
                if round != rounds:
                        working_array = perm_array(working_array)
                        print "Round {0} W (perm'ed):\t".format(round),working_array
                working_array = sub_array(working_array)
                print "Round {0} V (sub'ed):\t\t".format(round),working_array
                print

        # Print out the final round key and xor'ed result (plaintext)
        print "Round 1 Key:\t\t\t",get_key(key, 1)
        working_array = xor_array(working_array, get_key(key, 1))
        print("Plaintext (xor'ed):\t\t"), working_array