prime.py

import gmpy2


def get_prime(random_state, b, n=25):
    p = gmpy2.mpz_urandomb(random_state, b)
    while not gmpy2.is_prime(p, n):
        p = gmpy2.mpz_urandomb(random_state, b)
    return p


def get_rsa_params(random_state, bit_count, e=65537, n=25):
    p = get_prime(state, bit_count // 2)
    q = get_prime(state, bit_count // 2)

    n = p * q

    l = gmpy2.lcm(p - 1, q - 1)
    d = gmpy2.invert(e, l)

    return (n, e, d, p, q)


if __name__ == '__main__':
    state = gmpy2.random_state(42)

    n, e, d, p, q = get_rsa_params(state, 2048)

    msg = input("Please input message: ")
    m = int.from_bytes(msg.encode(), 'little')

    c = gmpy2.powmod(m, e, n)
    md = gmpy2.powmod(c, d, n)

    print(m)
    print(md)