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Title: Design and Implement A Symmetric Encryption Algorithm Based On Feistel

This document describes a symmetric encryption algorithm based on the Feistel structure. It defines functions for key generation, bitwise XOR, and binary-decimal conversion. It then encrypts and decrypts a sample plaintext using two rounds of Feistel networking, generating subkeys for each round and chaining the left and right halves.

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Amol Shinde
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27 views4 pages

Title: Design and Implement A Symmetric Encryption Algorithm Based On Feistel

This document describes a symmetric encryption algorithm based on the Feistel structure. It defines functions for key generation, bitwise XOR, and binary-decimal conversion. It then encrypts and decrypts a sample plaintext using two rounds of Feistel networking, generating subkeys for each round and chaining the left and right halves.

Uploaded by

Amol Shinde
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Title : Design and implement a symmetric encryption algorithm based on Feistel

structure.
Code :
import binascii
# Random bits key generation
def rand_key(p):
import random
key1 = ""
p = int(p)

for i in range(p):
temp = random.randint(0, 1)
temp = str(temp)
key1 = key1 + temp

return (key1)

# Function to implement bit exor


def exor(a, b):
temp = ""

for i in range(n):
if (a[i] == b[i]):
temp += "0"
else:
temp += "1"
return temp
# Defining BinarytoDecimal() function
def BinaryToDecimal(binary):
# Using int function to convert to string
string = int(binary, 2)
return string

# Feistel Cipher
PT = "Hello"
print("Plain Text is:", PT)

# Converting the plain text to ASCII


PT_Ascii = [ord(x) for x in PT]

# Converting the ASCII to 8-bit binary format


PT_Bin = [format(y, '08b') for y in PT_Ascii]
PT_Bin = "".join(PT_Bin)

n = int(len(PT_Bin) // 2)
L1 = PT_Bin[0:n]
R1 = PT_Bin[n::]
m = len(R1)

# Generate Key K1 for the first round


K1 = rand_key(m)

# Generate Key K2 for the second round


K2 = rand_key(m)

# first round of Feistel


f1 = exor(R1, K1)
R2 = exor(f1, L1)
L2 = R1

# Second round of Feistel


f2 = exor(R2, K2)
R3 = exor(f2, L2)
L3 = R2

# Cipher text
bin_data = L3 + R3
str_data = ' '

for i in range(0, len(bin_data), 7):


# slicing the bin_data from index range [0, 6]
# and storing it in temp_data
temp_data = bin_data[i:i + 7]

# passing temp_data in BinarytoDecimal() function


# to get decimal value of corresponding temp_data
decimal_data = BinaryToDecimal(temp_data)
str_data = str_data + chr(decimal_data)

print("Cipher Text:", str_data)


# Decryption
L4 = L3
R4 = R3

f3 = exor(L4, K2)
L5 = exor(R4, f3)
R5 = L4

f4 = exor(L5, K1)
L6 = exor(R5, f4)
R6 = L5
PT1 = L6 + R6

PT1 = int(PT1, 2)
RPT = binascii.unhexlify('%x' % PT1)
print("Retrieved Plain Text is: ", RPT)

Output :

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