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|Key sizes||2048 bits|
|Block sizes||128 bits|
|Best public cryptanalysis|
|Grossman & Tuckerman's slide attack uses at most 212 chosen plaintexts|
The cipher uses a block size of 128 bits, and a very large key size of 2048 bits. Like DES it has a 16-round Feistel network structure. The round function uses two fixed 4×4-bit S-boxes, chosen to be non-affine. The key is also treated as an 8×8-bit lookup table, using the first bit of each of the 8 bytes of the half-block as input. The nth bit of the output of this table determines whether or not the two nibbles of the nth byte are swapped after S-box substitution. All rounds use the same table. Each round function ends with a fixed permutation of all 64 bits, preventing the cipher from being broken down and analyzed as a system of simpler independent subciphers.
In 1977, Edna Grossman and Bryant Tuckerman cryptanalyzed NDS using the first known slide attack. This method uses no more than 4096 chosen plaintexts; in their best trial they recovered the key with only 556 chosen plaintexts.
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