import random
import math
import time

def gcd(a, b):
    while b != 0:
        a, b = b, a % b
    return a


def is_prime(num):
    if num == 2:
        return True
    if num < 2 or num % 2 == 0:
        return False
    for n in range(3, int(num ** 0.5) + 2, 2):
        if num % n == 0:
            return False
    return True

def get_d(e,phi):
    d = 1.2
    k = 1
    while math.floor(d) != math.ceil(d):
        d = (k * phi + 1) / e
        k = k + 1
    return int(d)


def generate_keypair(p, q):
    if not (is_prime(p) and is_prime(q)):
        raise ValueError('Both numbers must be prime.')
    elif p == q:
        raise ValueError('p and q cannot be equal')
    n = p * q
    phi = (p - 1) * (q - 1)

    e = random.randrange(1, phi)

    g = gcd(e, phi)
    while g != 1:
        e = random.randrange(1, phi)
        g = gcd(e, phi)
    d = get_d(e,phi)
    print("d = {} e = {} n = {}".format(d,e,n))
    return ((e, n), (d, n))


def encrypt(pk, plaintext):
    # Unpack the key into it's components
    key, n = pk

    b = [(char.encode("cp1251")) for char in plaintext]

    с = [ord(i) for i in b]

    return [(char ** key) % n for char in с]


def decrypt(pk, ciphertext):
    # Unpack the key into its components
    key, n = pk
    z = [ (i ** key) % n for i in ciphertext]
    return bytes(z).decode('cp1251')

if __name__ == '__main__':
    '''
    Detect if the script is being run directly by the user
    '''
    print("RSA Encrypter/ Decrypter")
    start_time = time.time()
    p = 17 # int(input("Enter a prime number (17, 19, 23, etc): "))
    q = 37 #int(input("Enter another prime number (Not one you entered above): "))
    print("p = {} q = {}".format(p,q))
    print("Generating your public/private keypairs now . . .")
    public, private = generate_keypair(p, q)
    print("Your public key is ", public, " and your private key is ", private)
    message =  "390 1037 583 1354 987" #input("Enter a message to encrypt with your private key: ")
    print("text to encript '{}'".format(message))
    encrypted_msg = encrypt(public, message)

    print("Your encrypted message is: ")
    print(''.join(map(lambda x: str(x), encrypted_msg)))
    print("Decrypting message with public key ", public, " . . .")
    print("Your message is:")
    s = decrypt(private, encrypted_msg)
    print( s)
    time_elapsed = time.time() - start_time

    print('Time of RSA5 %.9f' % (time_elapsed))