A modified stream generator for the GSM encryption algorithms A5/1 and A5/2

Ergüler, İmran (Dogus Author)A5/1 and A5/2 are the GSM encryption algorithms that protect user data transmission over air. However, both of the A5/1 and A5/2 were cryptanalized by using different attack techniques such as time-memory trade off, divide and conquer and correlation attacks. In this study, we present a modified version of the A5/1 and A5/2 with offering security improvements to the vulnerabilities of the algorithms. By changing just the clocking mechanism of the shift registers used in the algorithms, it is shown that known attacks techniques become impractical.European Association for Signal Processing (EURASIP), KAREL, TUBITAK, NORTEL Networks - Business Without Boundaries, ARGELA Technologies

State Transition Analysis of GSM Encryption Algorithm A5/1

A5/1 stream cipher is used in Global System for Mobile Communication(GSM) phones for secure communication. A5/1 encrypts the message transferred from a mobile user. In this paper, we present the implementation of cryptanalytic on A5/1 techniques such as minimized state recovery for recovering the session key. The number of state transitions/updations needed for a state S to reoccur is maintained in the lookup table. This table can be used to recover the initial state from which the keystream was produced. Experiments are carried out for reduced version, full A5/1 cipher on 3.20 GHz machine, and cluster computing facility

Performance and Statistical Analysis of Stream ciphers in GSM Communications

For a stream cipher to be secure, the keystream generated by it should be uniformly random with parameter 1/2.Statistical tests check whether the given sequence follow a certain probability distribution. In this paper, we perform a detailed statistical analysis of various stream ciphers used in GSM 2G,3G, 4G and 5G communications. The sequences output by these ciphers are checked for randomness using the statistical tests defined by the NIST Test Suite. It should also be not possible to derive any information about secret key and the initial state ofthe cipher from the keystream. Therefore, additional statistical tests based on properties like Correlation between Keystreamand Key, and Correlation between Keystream and IV are also performed. Performance analysis of the ciphers also has been done and the results tabulated. Almost all the ciphers pass the tests in the NIST test suite with 99% confidence level. For A5/3stream cipher, the correlation between the keystream and key is high and correlation between the keystream and IV is low when compared to other ciphers in the A5 family

Eavesdropping on GSM: state-of-affairs

In the almost 20 years since GSM was deployed several security problems have been found, both in the protocols and in the - originally secret - cryptography. However, practical exploits of these weaknesses are complicated because of all the signal processing involved and have not been seen much outside of their use by law enforcement agencies. This could change due to recently developed open-source equipment and software that can capture and digitize signals from the GSM frequencies. This might make practical attacks against GSM much simpler to perform. Indeed, several claims have recently appeared in the media on successfully eavesdropping on GSM. When looking at these claims in depth the conclusion is often that more is claimed than what they are actually capable of. However, it is undeniable that these claims herald the possibilities to eavesdrop on GSM using publicly available equipment. This paper evaluates the claims and practical possibilities when it comes to eavesdropping on GSM, using relatively cheap hardware and open source initiatives which have generated many headlines over the past year. The basis of the paper is extensive experiments with the USRP (Universal Software Radio Peripheral) and software projects for this hardware.Comment: 5th Benelux Workshop on Information and System Security (WISSec 2010), November 201

A Comparison of Time-Memory Trade-Off Attacks on Stream Ciphers

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