bit lookup tables. References Matthew Kwan, The Design of the ICE Encryption Algorithm, Fast Software Encryption 1997, pp. 69–82 . Bart van Rompay, Lars R. Knudsen and Vincent Rijmen, Differential Cryptanalysis of the ICE Encryption Algorithm, Fast Software Encryption 1998, pp270–283 (PDF). External links The ICE Home Page The ICE information slides Feistel ciphers