流密码的设计与分析:回顾、现状与展望

Design and Analysis of Stream Ciphers: Past, Present and Future Directions

流密码的设计与分析一直都是密码学中的核心问题之一.上世纪40年代,Shannon证明了一次一密体制在唯密文攻击下在理论上的完善保密性,激发了流密码研究的热潮,自此流密码的设计都是围绕着如何产生接近完全随机的密钥流序列来进行,发展出了基于线性反馈移位寄存器(LFSR)的若干设计范例,许多基于此而设计的流密码纷纷被提出,比如用于GSM通信安全的A5/1和蓝牙加密算法E0等,同时也出现了像RC4等基于随机洗牌的设计范式.在欧洲NESSIE和e STREAM计划之后,流密码的设计日趋多样化,大量基于非线性反馈移位寄存器(NFSR)和基于分组密码扩散与混淆模块而设计的算法相继被提出,以抵抗基于LFSR线性性质而发展的(快速)相关攻击与(快速)代数攻击等.本文将首先回顾流密码设计与分析的发展历程,系统地综述流密码设计与分析中的若干关键技术与方法,同时介绍了目前最新的研究成果,以及这个方向上目前需要解决的一些关键问题,最后试着展望了一下未来流密码的发展方向.

As one of the most important problems in cryptography, the design and analysis of stream ciphers has always been a hot and central research topic. In the 40's of last century, Shannon proved in theory that the one-time pad cipher is secure in the ciphertext-only scenario, and triggered the fervor in stream ciphers. Since then, how to generate the keystreams which look like the purely random sequences as close as possible becomes the key point. As a result, many stream ciphers based on linear feedback shift registers(LFSR) are proposed, e.g., GSM A5/1 and Bluetooth encryption algorithm E0. At the same time, the design paradigm like RC4 based on random shuffles has also appeared. After the European NESSIE and e STREAM projects, the design of stream ciphers gets more and more diversified. Many algorithms based on nonlinear feedback shift register(NFSR) and the confusion and diffusion principle in block ciphers have been proposed, which have good resistance against(fast) correlation and(fast) algebraic attacks. This paper first reviews the development history of the design and analysis of stream ciphers, and then reviews certain crucial technical methods with the latest research achievements, and some problems need to be solved in this direction. Finally, we try to foresee the future research directions in stream ciphers.