<p>In practice, we usually require two cryptosystems, an asymmetric one and a symmetric one, to encrypt a large confidential message. The asymmetric cryptosystem is used to deliver secret key <tmath>$SK$</tmath>, while the symmetric cryptosystem is used to encrypt a large confidential message with the secret key <tmath>$SK$</tmath>. In this article, we propose a simple cryptosystem which allows a large confidential message to be encrypted efficiently. Our scheme is based on the Diffie-Hellman distribution scheme, together with the ElGamal cryptosystem.</p>