I would like to encrypt data for a CD-Rom. Anyone's data can get on the CD-Rom by way of the encryption box. Likewise anyone could read the cypher data back from the CD-Rom. Given that every 2k block of data will be encrypted with the same key. Given that there are weak keys with the IDEA cypher. And given that someone could mount an adaptive chosen plaintext attack. Which of the following would be a good bet for a secure data CD-Rom? 1 - IDEA cypher using Cypher Feed Back for the 2k data block. Insuring that the Weak Keys are not used. 2 - A combination cypher consisting of... IDEA -> T -> IDEA -> T -> IDEA where each IDEA cypher is in Cypher Feed Back mode with it's own key. where each T mixes the bytes around in the 2K block based on a modulo sum of the 2k bytes. Would method two be too time consuming? Would I need to exclude the weak keys from the IDEA cyphers in the second method?