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Realtime A5/1 Attacks with Precomputed TablesM. Novotny, A. Rupp |
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| GSM communication is encrypted with A5/1 stream cipher. Many attack
scenarios against GSM have been proposed, however none of them was fully
implemented. The first real-world attack appears to be the smart
brute-force attack recently developed and implemented in COSY group,
U Bochum. When using COPACOBANA machine, the cipher can be broken in
several hours. Another approach is to use precomputed tables, denoted as time-memory trade-off (TMTO) tables. This method allows for very fast attack, e.g. A5/1 cipher might be broken in a couple of minutes. However, precomputation of TMTO tables demands extensive computation power and hence it may last from several weeks up to several thousands of years, depending on both the cipher and the computation platform. In our talk we will discuss variants of TMTO methods, their advantages and drawbacks with respect to the actual cipher and with respect to efficient hardware implementation. We will present a hardware engine calculating TMTO tables for A5/1. The engine was designed and implemented for COPACOBANA machine. We also will discuss the design tricks used to gain maximum performance of the machine. |
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