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题目：Time--Memory Trade-off Attack on the GSM A5/1 Stream Cipher Using Commodity GPGPU 

时间：2015年12月24日（周四）9:30 

地点：中科院信息工程所3号楼3224会议室 

摘要：Time--memory trade-off (TMTO) cryptanalysis is a powerful technique for practically breaking a variety of security systems in reality. There are mainly four general TMTO cryptanalysis methods, namely Hellman table cryptanalysis, rainbow table cryptanalysis, thin rainbow table cryptanalysis and thick rainbow table cryptanalysis, plus a few supplementary techniques that can be combined with a general method to produce possibly distinct TMTOs, like distinguished points. In this talk, we present a unified TMTO cryptanalysis, which we call unified rainbow table cryptanalysis, basing it on a unified rainbow table, then we describe its general combination with distinguished points, and finally we apply unified rainbow table cryptanalysis to the A5/1 stream cipher being used in the Global System for Mobile Communications (GSM). On a general-purpose graphics processing unit (GPGPU) computer with 3 NVIDIA GeForce GTX690 cards that cost about 15,000 United States dollars in total, we made a unified rainbow table of 984GB in about 55 days, and implemented a unified rainbow table attack that had an online attack time of 9 seconds with a success probability of 34% (or 56%) when using 4 (respectively, 8) known keystreams (of 114 bits long each). If two such tables of 984GB were generated, the attack would have an online attack time of 9 seconds with a success probability of 81% when using 8 known keystreams. The practical results show again that nowadays A5/1 is rather insecure in reality and GSM should no longer use it. 

报告人英文简介：Jiqiang Lu received a B.Sc. degree in Applied Mathematics from Yantai University (China) in 2000, a M.Eng. degree in Information and Communication Engineering from Xidian University (China) in 2003, and a Ph.D. degree from the University of London (UK) in 2008. He then worked sequentially as a postdoc at Eindhoven University of Technology (The Netherlands) and Ecole Normale Superieure (France). Currently, he is a scientist in the Institute for Infocomm Research (Singapopre). His research interests center on symmetric cryptology and information security. 

报告人中文简介：吕继强2000年本科毕业于烟台大学应用数学专业,2003年硕士毕业于西安电子科技大学通信与信息系统专业,2008年博士毕业于英国Royal Holloway, University of London信息安全专业。他先后在荷兰Eindhoven University of Technology和法国Ecole Normale Superieure从事博士后工作，目前是新加坡咨询通信研究院的科研人员。他的研究领域主要是对称密码学和相关的信息安全。