input: Write a function to create a Python application for encryption and decryption of strings. The application should take a string as input, and use a cipher text algorithm of choice to encrypt the string.
  from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt(plaintext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext)
  
  def decrypt(ciphertext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)
  
  assert encrypt(b'Hello, World!')
  assert decrypt(encrypt(b'Hello, World!'))==b'Hello, World!'
  assert encrypt(b'Testing encryption')
  assert decrypt(encrypt(b'Testing encryption'))==b'Testing encryption'
  assert encrypt(b'')
  assert decrypt(encrypt(b''))==b''
output: def encrypt(plaintext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext)
  
  def decrypt(ciphertext):
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)