input: Write a python function to encrypt and decrypt a message using RSA algorithm.
  assert decrypt((2753, 3233), encrypt((17, 3233), "HELLO")) == "HELLO"
  assert decrypt((2753, 3233), encrypt((17, 3233), "WORLD")) == "WORLD"
  assert decrypt((2753, 3233), encrypt((17, 3233), "PYTHON")) == "PYTHON"
output: def encrypt(key, plaintext):
      e, n = key
      ciphertext = [(ord(char) ** e) % n for char in plaintext]
      return ciphertext
  
  def decrypt(key, ciphertext):
      d, n = key
      plaintext = ''.join([chr((char ** d) % n) for char in ciphertext])
      return plaintext