input: from Crypto.Cipher import AES
  
  def encrypt(plaintext):
      """ Encrypts the given plaintext using AES encryption with a predefined key.
      >>> encrypt(b'HelloWorld')
      b'h\xede`k\xc1\xe6h\x1c\x1b`!8\niO\xd7'
      """
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.encrypt(plaintext)
  
  def decrypt(ciphertext):
      """ Decrypts the given ciphertext using AES decryption with a predefined key.
      >>> decrypt(b'h\xede`k\xc1\xe6h\x1c\x1b`!8\niO\xd7')
      b'HelloWorld'
      """
      key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)
output:     key = b'Sixteen byte key'
      cipher = AES.new(key, AES.MODE_ECB)
      return cipher.decrypt(ciphertext)