Ever since the National Security Agency released its SkipJack algorithm – once meant as the basis for the US Government’s ill- fated Clipper Chip scheme (CI No 3,439) – computer scientists have been examining the software to see just how secure it really is. Now a team led by Eli Biham of the computer science department at the Israel Institute of Technology has reported a successful attack on a SkipJack variant. Biham’s team first took three of the 320 XOR (exclusive-or) operations out of SkipJack to create SkipJack-3XOR. It turns out that this weakened form of the algorithm can be cracked in seconds on a personal computer. This is still a preliminary result, cautions the team, but it reiterates our earlier comment that SkipJack does not have a conservative design with a large margin of safety.
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