From: <nobody@vox.hacktic.nl>
Date: Tue, 28 Jun 94 14:35:02 PDT
To: cypherpunks@toad.com
Subject: A question about encryption methods.
Message-ID: <199406282134.AA26834@xs4all.hacktic.nl>
MIME-Version: 1.0
Content-Type: text/plain


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?