I'm looking for information about the A5 encryption algorithm used in GSM phones. Specifically: - How does the algorithm work and is its encryption methodology similar to any other well-known algorithms? - Is A5's implementation mandatory to produce an world-wide interoperable GSM device? - What are the variants of A5 (there was some discussion of less secure versions), how do they differ, and where are they used? - Are there any known weaknesses in or attacks on A5-encrypted GSM conversations? - Are there notable instances where GSM deployment was delayed or halted due to A5? (I remember hearing that such a delay happened in Australia, but I don't recall details.) Any related information, or pointers to related information, appreciated greatly. ________________________________________________________________________ Stephan Somogyi Mr Gyroscope Digital Media