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DES.py
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DES.py
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# -*- coding: utf-8 -*-
"""
Created on Tue Apr 2 19:24:06 2019
@author: Abd-Elrahman
"""
#choose test
test = 2
if (test == 1):
theKey = "133457799BBCDFF1"#the encryption and decryption key
theMsg = "0123456789ABCDEF"#massege to be encryption
theExp = "85E813540F0AB405"#expected cipher text
elif (test == 2):
theKey = "38627974656B6579"#the encryption and decryption key
theMsg = "6D6573736167652E"#massege to be encryption
theExp = "7CF45E129445D451"#expected cipher text
def generateSubKeys(key):
"""Generates the 16 subkeys from the key
Parameters
----------
the 64-bit key used for encryption and decryption
Returns
-------
list of 16 56-bit keys
"""
key = bin(int(key, 16))[2:].zfill(8)
while(len(key) < 64):
key = '0'+key
#the first permutation matrix
PC1 = [[57, 49, 41, 33, 25, 17, 9],
[1, 58, 50, 42, 34, 26, 18],
[10, 2, 59, 51, 43, 35, 27],
[19, 11, 3, 60, 52, 44, 36],
[63, 55, 47, 39, 31, 23, 15],
[7, 62, 54, 46, 38, 30, 22],
[14, 6, 61, 53, 45, 37, 29],
[21, 13, 5, 28, 20, 12, 4]]
#applyng the permutation matrix
key56 = ''
for i in range(8):
for j in range(7):
key56 += key[PC1[i][j]-1]
#deviding the 56-bit key into two parts left and right
l0 = key56[:28]
r0 = key56[28:]
#creating the 16 keys
leftShiftArray = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1]
lkeys = [l0[leftShiftArray[0]:]+ l0[:leftShiftArray[0]]]
rkeys = [r0[leftShiftArray[0]:] + r0[:leftShiftArray[0]]]
for i in range(1,16):
lkeys.append(lkeys[i-1][leftShiftArray[i]:] + lkeys[i-1][:leftShiftArray[i]])
rkeys.append(rkeys[i-1][leftShiftArray[i]:] + rkeys[i-1][:leftShiftArray[i]])
keys = []
for i in range(16):
keys.append(lkeys[i]+rkeys[i])
#applyring Second permutation matrix
PC2 = [[14, 17, 11, 24, 1, 5],
[3, 28, 15, 6, 21, 10],
[23, 19, 12, 4, 26, 8],
[16, 7, 27, 20, 13, 2],
[41, 52, 31, 37, 47, 55],
[30, 40, 51, 45, 33, 48],
[44, 49, 39, 56, 34, 53],
[46, 42, 50, 36, 29, 32]]
permkeys = []
for k in range(16):
bitString= ""
for i in range(8):
for j in range(6):
bitString += keys[k][PC2[i][j]-1]
permkeys.append(bitString)
return permkeys
def encrypt(msg, keys):
"""Generates cipher text
Parameters
----------
the massege to be encrypted and the 16 subkeys
Returns
-------
cipher text
"""
return des(msg, keys, True)
def decrypt(msg, keys):
"""Generates cipher text
Parameters
----------
the massege to be decrypted and the 16 subkeys
Returns
-------
plain text
"""
return des(msg, keys, False)
def des(message, keys,flag):
"""applies the des algorthm to generate the ciphre or plain text
Parameters
----------
the massege to be decrypted or encrypted, the 16 subkeys and boolean flag to determen the process (encryption or decryption)
Returns
-------
a string containing either plain text or cipher text
"""
#convert message into bit string
message = bin(int(message, 16))[2:].zfill(8)
while(len(message) < 64):
message = '0'+message
#switch to decryption if choosed
if(not flag):
keys = keys[::-1]
#initial permutation matrix
IP = [[58, 50, 42, 34, 26, 18, 10, 2],
[60, 52, 44, 36, 28, 20, 12, 4],
[62, 54, 46, 38, 30, 22, 14, 6],
[64, 56, 48, 40, 32, 24, 16, 8],
[57, 49, 41, 33, 25, 17, 9, 1],
[59, 51, 43, 35, 27, 19, 11, 3],
[61, 53, 45, 37, 29, 21, 13, 5],
[63, 55, 47, 39, 31, 23, 15, 7]]
#inverse permution matrix
IPinv = [[40, 8, 48, 16, 56, 24, 64, 32],
[39, 7, 47, 15, 55, 23, 63, 31],
[38, 6, 46, 14, 54, 22, 62, 30],
[37, 5, 45, 13, 53, 21, 61, 29],
[36, 4, 44, 12, 52, 20, 60, 28],
[35, 3, 43, 11, 51, 19, 59, 27],
[34, 2, 42, 10, 50, 18, 58, 26],
[33, 1, 41, 9, 49, 17, 57, 25]]
#appling IP to message
permMess = ""
for i in range(8):
for j in range(8):
permMess += message[IP[i][j]-1]
# message to lift and right
l0 = permMess[:32]
r0 = permMess[32:]
l = [l0]
r = [r0]
for i in range(1,17):
l.append(r[i-1])
r.append(xor(l[i-1],fun(r[i-1], keys[i-1])))
#creating the final text
rl = r[-1]+l[-1]
result =''
for i in range(8):
for j in range(8):
result += rl[IPinv[i][j]-1]
result = hex(int(result,2))[2:]
return result.upper()
def fun( right, key):
"""applies the function f(R_n, K_n)
Parameters
----------
the value of L_n-1 + f(R_n-1, k_n-1) where R_0 is the right half of the plain text, and the nth key
Returns
-------
32 bit string
"""
#expanding the message
expantion = [[32, 1, 2, 3, 4, 5],
[4, 5, 6, 7, 8, 9],
[8, 9, 10, 11, 12, 13],
[12, 13, 14, 15, 16, 17],
[16, 17, 18, 19, 20, 21],
[20, 21, 22, 23, 24, 25],
[24, 25, 26, 27, 28, 29],
[28, 29, 30, 31, 32, 1]]
exRight = ""
for i in range(8):
for j in range(6):
exRight += right[expantion[i][j] - 1]
#applynig xor between the message and the key
exRight = xor(exRight, key)
#applyin the x-boxes on the message
exRight = applySboxes(exRight)
p = [[16, 7, 20, 21],
[29, 12, 28, 17],
[1, 15, 23, 26],
[5, 18, 31, 10],
[2, 8, 24, 14],
[32, 27, 3, 9],
[19, 13, 30, 6],
[22, 11, 4, 25]]
result = "";
for i in range(8):
for j in range(4):
result += exRight[p[i][j] - 1]
return result
def applySboxes(string):
"""applies the sboxes to a key
Parameters
----------
48 bit key
Returns
-------
a 32 bit string
"""
parts =[]
rows = []
col = []
for i in range(8):
parts.append(string[i*6:(i+1)*6])
rows.append(parts[i][0]+parts[i][-1])
col.append(parts[i][1:-1])
sBoxes = [
#sbox 1
[[14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
[0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
[4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
[15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13]],
#sbox 2
[[15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10],
[3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5],
[0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15],
[13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9]],
#sbox 3
[[10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8],
[13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1],
[13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7],
[1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12]],
#sbox 4
[[7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15],
[13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9],
[10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4],
[3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14]],
#sbox 5
[[2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9],
[14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6],
[4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14],
[11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3]],
#sbox 6
[[12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11],
[10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8],
[9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6],
[4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13]],
#sbox 7
[[4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1],
[13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6],
[1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2],
[6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12]],
#sbox 8
[[13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7],
[1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2],
[7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8],
[2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11]]
]
holder = ""
s = ""
for i in range(8):
s += bin(sBoxes[i][int(rows[i],2)][int(col[i],2)])[2:].zfill(4)
while(len(s) % 4 != 0 and len(s) < 4 or s== ""):
s = '0'+s
holder += s
s = ''
return holder
def xor( s1, s2):
"""xor over two bit strings
Parameters
----------
two bit strings s1,s2
Returns
-------
a string contains the xor of s1,s2
"""
if(len(s1) != len(s2)):
raise Exception("can't apply xor function on non-equal strings")
s0 = ""
for i in range(len(s1)):
if(s1[i] == s2[i]):
s0 += '0'
else:
s0 += '1'
return s0
#calling the functions
subKeys = generateSubKeys(theKey)
theCph = encrypt(theMsg, subKeys)
thePlain = decrypt(theCph, subKeys)
#print the output
print("Key : " + theKey)
print("Message : " + theMsg)
print("Cipher : " + theCph)
print("Expected: " + theExp)
print("Plain : " + thePlain)