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Commit a418c20

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1 parent 02176ee commit a418c20

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2 files changed

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‎main.py

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

‎utils.py

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

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