<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def encrypt(self, plaintext):
 """Return ciphertext for given plaintext."""


        # String to bytes.
        plainbytes = plaintext.encode('utf8')

        # Compress plaintext bytes.
        compressed = zlib.compress(plainbytes)

        # Construct AES-GCM cipher, with 96-bit nonce.
        cipher = AES.new(self.cipher_key, AES.MODE_GCM, nonce=random_bytes(12))

        # Encrypt and digest.
        encrypted, tag = cipher.encrypt_and_digest(compressed)

        # Combine with nonce.
        combined = cipher.nonce + tag + encrypted

        # Encode as Base64.
        cipherbytes = base64.b64encode(combined)

        # Bytes to string.
        ciphertext = cipherbytes.decode('utf8')

        # Return ciphertext.
        return ciphertext