input: Write a function to implement an encryption and decryption application in Python. The application should take a string as input and use the AES encryption algorithm to encrypt and decrypt the string. The key should be a byte string 'Sixteen byte key'.
  
  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!')!=b'Hello, World!'
  assert decrypt(encrypt(b'Hello, World!'))==b'Hello, World!'
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)