  The rapid development of computer technology will be the whole world as a
whole, the widespread application of instant messaging technology to bring
great convenience to people's lives, while privacy protection has become a more
significant problem. For ordinary it's hard to equip themselves with a
cryptograph machine. In this paper, through in-depth study of elliptic curve
cryptosystem ECC and advanced encryption standard AES encryption algorithm,
according to the characteristics of public key cryptography, elliptic curve
version through the establishment of Diffie-Hellman key exchange protocol,
combined with AES, design a set of perfect forward secrecy mixed cryptograph
system .The system can guarantee the security of communication, easy to
implement, the operation speed is quick and the cost is low. At last, the
security of the system is analyzed under the environment of common network
attacks.
