完善保密密码体制的研究

Almost all presently-used cipher, including symmetric-key cryptosystems and public-key cryptosystems, are based on the model of computational security, they can theoretically be broken by an exhaustive key search. For instance, the security of the well-known RSA public-key cryptosystem is based on the (unproven) difficulty of factoring large integers, and many other cryptographic systems and protocols are based on the similarly unproven difficulty of computing discrete logarithms. These computationally secure systems are not guaranteed to be secure in the future, since new, better attacking techniques may be developed to reduce the security level of the system. On the other hand, the intractable problems mentioned above can be solved efficiently if quantum computers would come in being.Unconditional security is more desirable in cryptography than computational security for two reasons. First, for the former no assumption about enemy's computing power is needed, and second, perfect secrecy is unarguable the strongest definition of secrecy and hence the justification of a weaker definition of security (for instance that an enemy cannot guess any plaintext bit with probability of success greater than a specified bound) is avoid. Therefore, it is significant for us to focus our attention on the research of unconditional security.After a secret-key is agreed to between two parties, a one-time pad can be used to transmit messages with perfect secrecy, so the key to perfect secrecy is unconditional security secret key agreement. The main work in this project is as follows:(1) The properties and construction of each step, including advantage distillation, information reconciliation and privacy amplification, in unconditional secret-key agreement are studied, the relationships between these steps are showed.(2) The model of unconditionally-secure secret-key agreement against active adversaries over an insecure and not even authentic channel is studied.(3) Unconditionally-secure cryptographic primitive, like oblivious transfer, is researched.In addition, the theory, techniques of information hiding and sorts of electronic payment systems are also studied. The project has been basically completed. 26 papers, in which 2 papers is in international journal, 19 papers is in domestic core journals, 5 papers is in domestic ordinary journals, have been published, a book has been published.

本项目旨在突破现有密码系统所基于的计算安全模型，从信息理论安全角度研究完善保密的理论和实现，重点是认证信道和非认证信道上的无条件安全密钥协商的模型、协议及算法，最终实现一种完善保密密码系统。. 完善保密是唯一建立在无条件安全模型之上、可以攻击具有无限计算能力的敌手的密码体制，对它的研究将具有重要的理论和实际意义。