1.引言公开密钥密码体制提供的灵活程度不适用于一般体制(秘密密钥)。特别是公开密钥体制脱密所需要的密钥可随时改变,甚至在消息中间都可以进行。这就使得窃听的确很难进行。经常提到的公开密钥体制的缺点是由于需要处理大数值的数。所以速度缓慢(通常每秒几千比特)。因而就促使混合密码体制的发展。在这种体制中,密钥通过一个缓慢的公开密钥系统变换后接着用在一般快速系统 1. Introduction The degree of flexibility provided by the public key cryptosystem does not apply to the general system (secret key). In particular, the key needed to decrypt a public key system can be changed at any time, even in the middle of a message. This makes it really difficult to eavesdropping. The shortcomings of the often-mentioned public-key system are due to the need to handle large numbers of numbers. So slow (usually a few thousand bits per second). Thus prompting the development of mixed cryptosystem. In this system, the key is transformed by a slow public key system and then used in a general fast system