Chinese Journal of Computers   Full Text
Title	EM Frequency Domain Template Analysis on Cipher Chips
Authors	DENG Gao-Ming ZHAO Qiang ZHANG Peng CHEN Kai-Yan LIU Xiao-Qin
Address	(Department of Computer Engineering, Ordnance Engineering College, Shijiazhuang 050003)
Year	2009
Issue	No.4(602—610)
Abstract &   Background	Abstract A general countermeasures against time domain side channel attacks is to insert random delays into the executing sequence of cipher algorithm, in which the interesting operations will occur at different time in multi runs of the cipher. To break this countermeasures, this paper analyzes the generation of the electromagnetic(EM) emissions of cipher chips and its dependence with the data operated in chips, with the law of energy conservation, this paper finds out the fact that the data dependence of the EM signals emissed from the cipher chips can remain when it is transformed from time domain to frequency domain, and that the data dependence in frequency domain signals will not be affected by inserting random delays into time domain signals. With this property of the frequency domain signals, this paper presents a new EM frequency domain template analysis. Experiments of EM frequency domain template analysis on a micro-controller (AT89C52) implemented RC4 show that the genuine key of RC4 can still be recovered after inserting random delays in source code, while template analysis in time domain is invalidation. Furthermore, the time complexity of this new template analysis is no more than the analysis in time domain. Keywords side channel attacks; EM; frequency domain template analysis; cryptographic chips; RC4 Background This work is supported by the National Natural Science Foundation of China under grant No.60571037, and the National High Technology Research and Development Program (863 Program) of China under grant No.2007AA01Z454. They aim to evaluate the security of cipher chips under side channel attacks, especially under power analysis and EM analysis. In these two programs, the power model of CMOS device was built with Hamming Weight or Hamming Distance model, and popular ciphers such as DES, AES, RSA and RC4 implemented in a micro-controller were analyzed with side channel attacks, especially power analysis and EM analysis, and the experiments showed a good result. Besides, a formal security model for cipher under side channel attack is analyzed, and it is hopeful to evaluate the security of cipher chips under side channel attack.