3-round Simple DES / CBC 모드

이번엔 Simple DES 모델을 바탕으로 python 코드를 짜보았다.

생각보다 어렵지 않은 과정이어서 흥미로웠다.

cbc모드도 같이 구현했다.

import random

def expansion(pblock):

        left = []

        

        left = pblock[:2]

        left.append(pblock[3])

        left.append(pblock[2])

        left.append(pblock[3])

        left.append(pblock[2])

        left.extend(pblock[4:])

        return left

        

def left_half(pblock):

    num = int(len(pblock)/2)

    return pblock[:num]

def right_half(pblock):

    num = int(len(pblock)/2)

    return pblock[num:]

def xor(pblock, key):

    new = ''

    for bit, key_bit in zip(pblock, key):

        new += str(bit ^ key_bit)

    return list(map(int,new))

def sbox1(bits):

    sbox1 = [[[1,0,1], [0,1,0], [0,0,1], [1,1,0], [1,1,0], [1,0,0], [1,1,1], [0,0,0]],

         [[0,0,1], [1,0,0], [1,1,0], [0,1,0], [0,0,0], [1,1,1], [1,0,1], [0,1,1]]]

      

    index = bits[1]*4 + bits[2]*2 + bits[3]*1

    

    return sbox1[bits[0]][index]

def sbox2(bits):

    sbox2 = [[[1,0,0], [0,0,0], [1,1,0], [1,0,1], [1,1,1], [0,0,1], [0,1,1], [0,1,0]],

         [[1,0,1], [0,1,1], [0,0,0], [1,1,1], [1,1,0], [0,1,0], [0,0,1], [1,0,0]]]

             

    col = bits[1]*4+bits[2]*2+bits[3]*1

    return sbox2[bits[0]][col]

def key_shift_enc(key) :

    key_s =  key[1:]

    key_s.append(key[0])

    return key_s

def key_shift_dec(key) :

    

    key_s = key[:8]

    key_s.insert(0, key[-1])

    return key_s

def function(key, pblock):

    key = key[:8]

    rpblock = pblock[6:]

    lpblock = pblock[:6]

    bits = expansion(rpblock)

    bits = xor(bits, key)

    left = left_half(bits)

    right = right_half(bits)

    left = sbox1(left)

    right = sbox2(right)

    bits = left + right

    bits = xor(bits, lpblock)

    bits = rpblock + bits

    

    return bits

def sdes_encrypt(key, pblock):

    pblock_tmp = []

    

    pblock = function(key, pblock)

    

    key = key_shift_enc(key)

    pblock = function(key, pblock)

    

    key = key_shift_enc(key)

    pblock = function(key, pblock)

    pblock_tmp.extend(pblock[6:])

    pblock_tmp.extend(pblock[:6])

    pblock = pblock_tmp

    return pblock

def sdes_decrypt(key, pblock):

    

    key3 = []

    pblock_tmp = []

    

    key3 = key[2:]

    key3.extend(key[:2])

    key = key3

    

    pblock = function(key, pblock)

    

    key = key_shift_dec(key)

    pblock = function(key, pblock)

    

    key = key_shift_dec(key)

    pblock = function(key, pblock)

    pblock_tmp.extend(pblock[6:])

    pblock_tmp.extend(pblock[:6])

    pblock = pblock_tmp

    return pblock

def cbc_genkey():

    numlist = [random.randint(0,1) for _ in range(9)]

    return numlist

def cbc_encrypt(key, IV, pblock):

    pblock_tmp = []

    result = []

    cnt = 0

    IV_tmp = IV

    while True:

        pblock_tmp = pblock[cnt*12:cnt*12+12]

        if(len(pblock)/12 == cnt):

                break

        else:

                pblock_tmp = xor(pblock_tmp, IV_tmp)

                pblock_tmp = sdes_encrypt(key, pblock_tmp)

                IV_tmp = pblock_tmp

                cnt += 1

                result.extend(pblock_tmp)

    return result

def cbc_decrypt(key, IV, cblock):

    

    cblock_tmp = []

    result = []

    cnt = 0

    IV_tmp = []

    while True:

        cblock_tmp = cblock[cnt*12:cnt*12+12]

        if(len(cblock)/12 == cnt):

                break

        else:

                cblock_tmp = sdes_decrypt(key, cblock_tmp)

                if(cnt == 0):

                    cblock_tmp = xor(cblock_tmp, IV)

                else:

                    cblock_tmp = xor(cblock_tmp, IV_tmp)

                    

                IV_tmp = cblock[cnt*12:cnt*12+12]

                cnt += 1

                result.extend(cblock_tmp)

                

    return result