Initial

Author: ahmed-hassan19

main.py

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+from utils import *
+import random
+
+primes = [i for i in range(100, 500) if is_prime(i)]
+p = random.choice(primes)
+q = random.choice(primes)
+message = input('Enter the text to be encrypted: ')
+
+n = p*q
+k = (p-1)*(q-1) 
+
+for e in range(2, k):
+    if gcd(e, k) == 1:
+        break
+
+public_key = (n, e)
+
+_, b, _ = extended_gcd(e, k)
+if b < 0:
+    b = b + k
+private_key = (n, b)
+
+encrypted = encrypt(public_key, message)
+print(f'Encrypted message: {"".join(str(s) for s in encrypted)}')
+
+decrypted = decrypt(private_key, encrypted)
+print(f'Decrypted message: {"".join(str(s) for s in decrypted)}')

utils.py

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+def is_prime(x):
+    '''
+    Takes an integer x and returns True if x is a prime number
+    and Flase if x is not a prime number.
+    '''
+    for i in range(2, x-1):
+        if x % i == 0:
+            return False
+    else:
+        return True
+
+def gcd(a, b):
+    '''
+    Computes the Greates Common Divisor (gcd) between integers a, b.
+    '''
+    if b == 0:
+        return a 
+    else: 
+        return gcd(b, a%b) 
+
+def extended_gcd(x, y):
+    '''
+    Extended Euclidean algortihm between integers x, y to find
+    the modular multiplicative inverse d of x under modulo y. 
+    '''
+    if y == 0:   
+        return x, 1, 0
+             
+    d, a, b = extended_gcd(y, x % y)  
+     
+    return d, b, a - (x // y) * b
+
+def encrypt(public_key, message):
+    '''
+    Encryptes a string message using a public_key as a tuple of (n, e).
+    '''
+    encrypted = []
+    for character in message:
+        int_message = ord(character)
+        n, e = public_key
+        c = pow(int_message, e) % n 
+        encrypted.append(c)
+    return encrypted
+
+def decrypt(private_key, encrypted):
+    '''
+    Decryptes a string message using a private_key as a tuple of (n, d).
+    '''
+    decrypted = []
+    for character in encrypted:
+        n, d = private_key
+        int_message = pow(character, d) % n
+        message = chr(int_message)
+        decrypted.append(message)
+    return decrypted