RSA.py

import random

import math
 
# A set will be the collection of prime numbers,
# where we can select random primes p and q

prime = set()
 

public_key = None

private_key = None

n = None
 
# We will run the function only once to fill the set of
# prime numbers

def primefiller():

    # Method used to fill the primes set is Sieve of

    # Eratosthenes (a method to collect prime numbers)

    seive = [True] * 250

    seive[0] = False

    seive[1] = False

    for i in range(2, 250):

        for j in range(i * 2, 250, i):

            seive[j] = False
 

    # Filling the prime numbers

    for i in range(len(seive)):

        if seive[i]:

            prime.add(i)
 
 
# Picking a random prime number and erasing that prime
# number from list because p!=q

def pickrandomprime():

    global prime

    k = random.randint(0, len(prime) - 1)

    it = iter(prime)

    for _ in range(k):

        next(it)
 

    ret = next(it)

    prime.remove(ret)

    return ret
 
 

def setkeys():

    global public_key, private_key, n

    prime1 = pickrandomprime()  # First prime number

    prime2 = pickrandomprime()  # Second prime number
 

    n = prime1 * prime2

    fi = (prime1 - 1) * (prime2 - 1)
 

    e = 2

    while True:

        if math.gcd(e, fi) == 1:

            break

        e += 1
 

    # d = (k*Φ(n) + 1) / e for some integer k

    public_key = e
 

    d = 2

    while True:

        if (d * e) % fi == 1:

            break

        d += 1
 

    private_key = d
 
 
# To encrypt the given number

def encrypt(message):

    global public_key, n

    e = public_key

    encrypted_text = 1

    while e > 0:

        encrypted_text *= message

        encrypted_text %= n

        e -= 1

    return encrypted_text
 
 
# To decrypt the given number

def decrypt(encrypted_text):

    global private_key, n

    d = private_key

    decrypted = 1

    while d > 0:

        decrypted *= encrypted_text

        decrypted %= n

        d -= 1

    return decrypted
 
 
# First converting each character to its ASCII value and
# then encoding it then decoding the number to get the
# ASCII and converting it to character

def encoder(message):

    encoded = []

    # Calling the encrypting function in encoding function

    for letter in message:

        encoded.append(encrypt(ord(letter)))

    return encoded
 
 

def decoder(encoded):

    s = ''

    # Calling the decrypting function decoding function

    for num in encoded:

        s += chr(decrypt(num))

    return s
 
 

if __name__ == '__main__':

    primefiller()

    setkeys()

    # message = "Test Message"

    # Uncomment below for manual input

    message = input("Enter the message\n")

    # Calling the encoding function

    coded = encoder(message)
 

    print("Initial message:")

    print(message)

    print("\n\nThe encoded message(encrypted by public key)\n")

    print(coded)

    print(''.join(str(p) for p in coded))

    print("\n\nThe decoded message(decrypted by public key)\n")

    print(''.join(str(p) for p in decoder(coded)))