implementation of RSA public-key cryptosystem in python

rsa.py

import argparse

class RSA:

    def __init__(self, p, q, e):
        self.p, self.q, self.e = p, q, e
        self.n = p * q
        self.phi = (p - 1) * (q - 1)
        self.d = e ** (self.phi - 1) % self.phi

    def encrypt(self, m):
        return m ** self.e % self.n

    def decrypt(self, c):
        return c ** self.d % self.n


parser = argparse.ArgumentParser(prog='RSA', description='RSA public-key cryptosystem implementation')
parser.add_argument('-p', help='Large Prime p', type=int, required=True)
parser.add_argument('-q', help='Large Prime q', type=int, required=True)
parser.add_argument('-e', help='Exponent where 1 < E < P * Q', type=int, required=True)
parser.add_argument('-k', help='Encrypt or Decrypt?', choices=['encrypt', 'decrypt'], required=True)
parser.add_argument('-x', help='Payload (to encrypt or decrypt)', type=int, required=True)

args = parser.parse_args()

rsa = RSA(args.p, args.q, args.e)

r = {'enc': rsa.encrypt(args.x),
     'dec': rsa.decrypt(args.x)}

print(r[args.k])