With the rapidly development of computer network technology and the widely use of network technology in every walk of life , people transmit data through computer network more and more frequently , including all kinds of secret information ( for example , military secret ; bussiness secret ; personal private information ) . today , as a result of poor security of our network system , we can not prevent the transmittied information from stealing and modifying unlawful . thus , the computer network technology is applied to our daily life restrictedly . recently , many network applications with voip ( for example msn messenger ; dialpad ; distributed multipoint multimedia conferences ) take no measures to encrypt their data 随着计算机网络技术的迅猛发展和网络技术在各行各业中的广泛应用，人们通过计算机网络传输数据日益增加，其中包含了各种机密信息(例如军事机密信息、商业机密信息、个人隐私信息等) 。由于目前的网络系统缺乏足够的安全性，不能有效防止网络上所传输的信息被非法窃取和修改，因而极大地限制了计算机网络技术在日常工作中的应用。当前，基于voip技术的各种网络应用，如msnmessenger ， dialpad ，以及一些分布式多媒体会议系统，竟然未采取任何加密措施
