DES_Decrypt.py

import binascii
import math
import secrets

# String to hexadecimal converstion
def str2hex(word):
    word_2byte = bytes(word,'ascii')  
    word_hex = binascii.hexlify(word_2byte).decode().upper()
    return word_hex
    
# Hexadecimal to binary conversion
def hex2bin(s):
	mp = {'0' : "0000",
		'1' : "0001",
		'2' : "0010",
		'3' : "0011",
		'4' : "0100",
		'5' : "0101",
		'6' : "0110",
		'7' : "0111",
		'8' : "1000",
		'9' : "1001",
		'A' : "1010",
		'B' : "1011",
		'C' : "1100",
		'D' : "1101",
		'E' : "1110",
		'F' : "1111" }
	bin = ""
	for i in range(len(s)):
		bin = bin + mp[s[i]]
	return bin
	
# Binary to hexadecimal conversion
def bin2hex(s):
	mp = {"0000" : '0',
		"0001" : '1',
		"0010" : '2',
		"0011" : '3',
		"0100" : '4',
		"0101" : '5',
		"0110" : '6',
		"0111" : '7',
		"1000" : '8',
		"1001" : '9',
		"1010" : 'A',
		"1011" : 'B',
		"1100" : 'C',
		"1101" : 'D',
		"1110" : 'E',
		"1111" : 'F' }
	hex = ""
	for i in range(0,len(s),4):
		ch = ""
		ch = ch + s[i]
		ch = ch + s[i + 1]
		ch = ch + s[i + 2]
		ch = ch + s[i + 3]
		hex = hex + mp[ch]
	return hex

# Binary to decimal conversion
def bin2dec(binary):

	decimal, i = 0, 0
	while(binary != 0):
		dec = binary % 10
		decimal = decimal + dec * pow(2, i)
		binary = binary//10
		i += 1
	return decimal

# Decimal to binary conversion
def dec2bin(num):
	res = bin(num).replace("0b", "")
	if(len(res)%4 != 0):
		div = len(res) / 4
		div = int(div)
		counter =(4 * (div + 1)) - len(res)
		for i in range(0, counter):
			res = '0' + res
	return res

# Permute function to rearrange the bits
def permute(k, arr, n):
	permutation = ""
	for i in range(0, n):
		permutation = permutation + k[arr[i] - 1]
	return permutation

# shifting the bits towards left by nth shifts
def shift_left(k, nth_shifts):
	s = ""
	for i in range(nth_shifts):
		for j in range(1,len(k)):
			s = s + k[j]
		s = s + k[0]
		k = s
		s = ""
	return k

# calculating xow of two strings of binary number a and b
def xor(a, b):
	ans = ""
	for i in range(len(a)):
		if a[i] == b[i]:
			ans = ans + "0"
		else:
			ans = ans + "1"
	return ans


def encrypt(pt, rkb, rk):
	pt = hex2bin(pt)
	
	# Initial Permutation
	pt = permute(pt, initial_perm, 64)
	print("After initial permutation", bin2hex(pt))
	
	# Splitting
	left = pt[0:32]
	right = pt[32:64]
	for i in range(0, 16):
		# Expansion D-box: Expanding the 32 bits data into 48 bits
		right_expanded = permute(right, exp_d, 48)
		
		# XOR RoundKey[i] and right_expanded
		xor_x = xor(right_expanded, rkb[i])

		# S-boxex: substituting the value from s-box table by calculating row and column
		sbox_str = ""
		for j in range(0, 8):
			row = bin2dec(int(xor_x[j * 6] + xor_x[j * 6 + 5]))
			col = bin2dec(int(xor_x[j * 6 + 1] + xor_x[j * 6 + 2] + xor_x[j * 6 + 3] + xor_x[j * 6 + 4]))
			val = sbox[j][row][col]
			sbox_str = sbox_str + dec2bin(val)
			
		# Straight D-box: After substituting rearranging the bits
		sbox_str = permute(sbox_str, per, 32)
		
		# XOR left and sbox_str
		result = xor(left, sbox_str)
		left = result
		
		# Swapper
		if(i != 15):
			left, right = right, left
		print("Round ", i + 1, " ", bin2hex(left), " ", bin2hex(right), " ", rk[i])
	
	# Combination
	combine = left + right
	
	# Final permutation: final rearranging of bits to get cipher text
	cipher_text = permute(combine, final_perm, 64)
	return cipher_text

def startDesDecryption(pt,key):
    print("="*50)
    print("==========================>>>>>>>> Start decryption process...")
    #pt = "Your lips are smoother than vaseline"
    #key = secrets.token_hex(8).upper()
    print("The Key: ",key)
    #pt = str2hex(pt)
    print("The cipher: ",pt)
    cyc = math.ceil(len(pt)/16)
    st = 0
    ptCopy = pt
    result = ""
    ciphers = ""
    
    for i in range(0,cyc):
        
        pt = ptCopy
        pt = ptCopy[st:st+16]
        st+=16
        #print("===================================================> :",pt)
    
        if len(pt) < 16:
            for i in range(len(pt),16):
                pt = pt + '0'
                   
        print("The new cycle :",pt)
        # Table of Position of 64 bits at initial level: Initial Permutation Table
        global initial_perm,exp_d,per,sbox,final_perm
        
        initial_perm = [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]
        
        # Expansion D-box Table
        exp_d = [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 ]
        
        # Straight Permutation Table
        per = [ 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 ]
        
        # S-box Table
        sbox = [[[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] ] ]
        
        # Final Permutation Table
        final_perm = [ 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 ]
        
        
        # Key generation
        # --hex to binary
        key = hex2bin(key)
        
        # --parity bit drop table
        keyp = [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 ]
        
        # getting 56 bit key from 64 bit using the parity bits
        key = permute(key, keyp, 56)
        
        # Number of bit shifts
        shift_table = [1, 1, 2, 2,
        				2, 2, 2, 2,
        				1, 2, 2, 2,
        				2, 2, 2, 1 ]
        
        # Key- Compression Table : Compression of key from 56 bits to 48 bits
        key_comp = [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 ]
        
        # Splitting
        left = key[0:28] # rkb for RoundKeys in binary
        right = key[28:56] # rk for RoundKeys in hexadecimal
        
        rkb = []
        rk = []
        for i in range(0, 16):
        	# Shifting the bits by nth shifts by checking from shift table
        	left = shift_left(left, shift_table[i])
        	right = shift_left(right, shift_table[i])
        	
        	# Combination of left and right string
        	combine_str = left + right
        	
        	# Compression of key from 56 to 48 bits
        	round_key = permute(combine_str, key_comp, 48)
        
        	rkb.append(round_key)
        	rk.append(bin2hex(round_key))
        
        #cipher_text = bin2hex(encrypt(pt, rkb, rk))
        
        print("Decryption")
        rkb_rev = rkb[::-1]
        rk_rev = rk[::-1]
        text = bin2hex(encrypt(pt, rkb_rev, rk_rev))
        #print("Plain Text : ",text)
        result+= text
    
    #print("The Plain Text: ",result)
    return result

#pt = "D1A87D37F5B6BFE1BDD5E90D454BF10A"
#key = "AABB09182736CCDD"
#key = secrets.token_hex(8).upper()
#cipher = startDesDecryption(pt,key)  
#print("The Plain Text: ",cipher)
#print(bytes.fromhex(cipher).decode('utf-8'))
####