A Practical-Time Attack on the A5/3 Cryptosystem Used in Third Generation GSM Telephony

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The privacy and security of GSM cellular telephony is protected by the A5 family of cryptosystems. The first two members of this family, A5/1 (Developed primarily for European markets) and A5/2 (Developed primarily for export markets) were designed in the late 1980's in an opaque process and were kept secret until they were reverse engineered in 1999 from actual handsets. Once published, it became clear that A5/2 provided almost no security, and A5/1 could be attacked with practical complexity by a variety of techniques.