DES Python Script

To use below python code, copy & paste to any text editor (e.g. Sublime Text) as a python file. Then, all you need to do is to run on your command line or terminal (Pyhton3 needs to be installed). Have Fun !

#DataEncryptionStandard Encryption Protocol Python(3.6) Implementation by otapsin for CryptoQuantus.
#Adapted from, ""https://academic.csuohio.edu/yuc/security/Chapter_06_Data_Encription_Standard.pdf""

#Initial Permutation Matrix (64bits).
P_i = [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] #This table specifies the input permutation on a 64-bit block. 
      #The meaning is as follows: the first bit of the output is taken from the 58th bit of the input; the second bit from the 50th bit, and so on, with the last bit of the output taken from the 7th bit of the input.
      #This information is presented as a table for ease of presentation; it is a vector, not a matrix.

#Final Permutation Matrix(After 16 Rounds)(64bits).
P_f = [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] #The final permutation is the inverse of the initial permutation; the table is interpreted similarly.

#Key Generator Algorithm.
#PermutedChoice Matrices.
#Initial Permutation Made on The Key(56bits).
PC_1 =  [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]
#Permutation Applied on The Shifted Key To get K_(i+1)(48bits).
PC_2 = [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]
#Expansion Funciton Matrix to Apply the XOR with K_i (32bits to expand 48bits).
E =  [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]
#Substitution Box.
S_box = [
         
[[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],
],

[[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],
],

[[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],
],

[[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],
],  

[[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],
], 

[[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],
], 

[[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],
],
   
[[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],
]
]

#Permutation made after each SBox substitution for each round(28bits).
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]
#Matrix of shifts for each round of keys(16bits).
SHIFT = [1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1]

def str_to_bit_array(text): #Convert a string into a list of bits.
    array = list()
    for char in text:
        binval = binvalue(char, 8) #Get the character value on one byte.
        array.extend([int(x) for x in list(binval)]) #Adding the bits to the final list.
    return array
def bit_array_to_str(array): #Re-creates the string from the bit array.
    res = ''.join([chr(int(y,2)) for y in [''.join([str(x) for x in _bytes]) for _bytes in  nsplit(array,8)]])   
    return res
def binvalue(val, bitsize): #Returns the binary value as a string of the given size.
    binval = bin(val)[2:] if isinstance(val, int) else bin(ord(val))[2:]
    if len(binval) > bitsize:
        raise "Binary value is too large"
    while len(binval) < bitsize:
        binval = "0"+binval #Add as many 0 as needed to get the wanted size(padding).
    return binval
def nsplit(s, n): #Split a list into sublists of size n.
    return [s[k:k+n] for k in range(0, len(s), n)]

ENCRYPT=1
DECRYPT=0

class des():
    def __init__(self):
        self.password = None
        self.text = None
        self.keys = list()
        
    def run(self, key, text, action=ENCRYPT, padding=False):
        if len(key) < 8:
            raise "Key Should be 8 bytes long !"
        elif len(key) > 8:
            key = key[:8] #If the size of the key is above 8bytes, cuts to be 8bytes long.
        
        self.password = key
        self.text = text
        
        if padding and action==ENCRYPT:
            self.addPadding()
        elif len(self.text) % 8 != 0: #If not, padding specified data size must be multiple of 8 bytes.
            raise "Data size should be multiple of 8 !"
        
        self.generatekeys() #Generates all the keys.
        text_blocks = nsplit(self.text, 8) #Splits the text in blocks of 8 bytes.
        result = list()
        for block in text_blocks: #Loops over all the blocks of data.
            block = str_to_bit_array(block) #Converts the block in bit array.
            block = self.pmt(block,P_i) #Applies the initial permutation.
            l, r = nsplit(block, 32) # l(LEFT),r(RIGHT).
            tmp = None
            for i in range(16): #16 rounds.
                r_e = self.expand(r, E) #Expand r to match K_i size (48bits).
                if action == ENCRYPT:
                    tmp = self.xor(self.keys[i], r_e) #If encrypting,uses K_i.
                else:
                    tmp = self.xor(self.keys[15-i], r_e)#If decrypting,start by the last key.
                tmp = self.substitute(tmp) #Method that will apply the SBOXes
                tmp = self.pmt(tmp, P)
                tmp = self.xor(l, tmp)
                l = r
                r = tmp
            result += self.pmt(r+l, P_f) #Does the last permutation and appends the result to result.
        final_res = bit_array_to_str(result)
        if padding and action==DECRYPT:
            return self.removePadding(final_res) #Removes the padding,if decrypt and padding are true.
        else:
            return final_res #Returns the final string of data ciphered or deciphered.
    def substitute(self, r_e): #Substitutes bytes by using SBOX.
        subblocks = nsplit(r_e, 6) #Splits bit array into sublist of 6 bits.
        result = list()
        for i in range(len(subblocks)): #For all the sublists
            block = subblocks[i]
            row = int(str(block[0])+str(block[5]),2)#Get the row with the first and last bit
            column = int(''.join([str(x) for x in block[1:][:-1]]),2) #Column is the 2,3,4,5th bits
            val = S_box[i][row][column] #Take the value in the SBOX appropriated for the round (i)
            bin = binvalue(val, 4)#Convert the value to binary
            result += [int(x) for x in bin]#And append it to the resulting list
        return result
        
    def pmt(self, block, table):
        return [block[x-1] for x in table]
    
    def expand(self, block, table): #Does the exact same thing than permutation.
        return [block[x-1] for x in table]
    
    def xor(self, t1, t2): #Applies a XOR and returns the resulting list.
        return [x^y for x,y in zip(t1,t2)]
    
    def generatekeys(self): #Algorithm that generates all the keys.
        self.keys = []
        key = str_to_bit_array(self.password)
        key = self.pmt(key, PC_1) #Applies the initial permutation on the key.
        l, r = nsplit(key, 28) #Splits it in to left(l) and right(r).
        for i in range(16): #Applies the 16 rounds.
            l, r = self.shift(l, r, SHIFT[i]) #Applies the shift w.r.t the round.
            tmp = l + r #Merges them.
            self.keys.append(self.pmt(tmp, PC_2)) #Applies the permutation to get the K_i.

    def shift(self, l, r, n): #Shifts a list of the given value.
        return l[n:] + l[:n], r[n:] + r[:n]
    
    def addPadding(self): #Adds padding to the datas by using PKCS5.
        pad_len = 8 - (len(self.text) % 8)
        self.text += pad_len * chr(pad_len)
    
    def removePadding(self, data): #Removes the padding of the plain text (If there is padding).
        pad_len = ord(data[-1])
        return data[:-pad_len]
    
    def encrypt(self, key, text, padding=True):
        return self.run(key, text, ENCRYPT, padding)
    
    def decrypt(self, key, text, padding=True):
        return self.run(key, text, DECRYPT, padding)
 
welcome = int(input("Welcome, to continue, Which year 'CryptoQuantus' was established ? :"))
print (welcome)

if welcome != int("2019"):
   print("Actually 2019 :D")
elif __name__ == '__main__':
     key = input ("Enter your 8 Character-Key :")
     text= input ("Plaintext:")
     d = des()
     ciphered = d.encrypt(key,text,padding=True) 
     plain = d.decrypt(key,ciphered,padding=True) 
     print ("Plaintext: ", plain)
     print ("Ciphertext %r" % ciphered)
     print ("by otapsin")

O.S. Tapsin