前言从本世纪六十年代末开始发展起来的算法复杂性理论,至今还不足二十年的历史。但其发展之速、应用之广乃是令人难以想象的。毫不例外,密码学领域也已受到它的冲击,得到前进的动力。C.仙农对保密学的发展有着巨大的贡献,他的理论至今仍有指导意义。但是近些年来,人们又试图把密码编码学的保密性建立在算法复杂性理论之上,这就产生了计算上保密的密码体制。这种体制和建立在仙农理论之上的密码体制的主要区别是:后者期 Preface The theory of algorithmic complexity developed since the late 1960s is still less than two decades old. However, its rapid development and wide application are unimaginable. As no exception, the field of cryptography has also been hit by it and has been motivated to move forward. C. Xiannong has made tremendous contribution to the development of confidential science, and his theory still has guiding significance. However, in recent years, attempts have been made to establish the confidentiality of cryptography based on the theory of algorithmic complexity, resulting in a cryptographically secure cryptographic system. The main difference between this system and the cryptosystem based on the theory of celestial farming is that of the latter period