ICE (cipher)

ICE, short for Information Concealment Engine, is a symmetric-key block cipher that Matthew Kwan published in 1997. It is built as a Feistel network, in the same family of structure as the Data Encryption Standard, but it adds a key-dependent bit permutation to the round function, and that permutation is arranged so that software can compute it efficiently. The standard version works on 64-bit blocks with a 64-bit key and 16 rounds. A faster variant called Thin-ICE uses only 8 rounds, and an open-ended family named ICE-n uses 16n rounds with a key of 64n bits. The design is not covered by patents and its source code was placed in the public domain. Published cryptanalysis by Van Rompay and colleagues in 1998 used differential methods: it recovered the key of Thin-ICE from chosen plaintexts and reached an attack on 15 of the 16 rounds of the standard cipher, which leaves the full cipher unbroken by that work.