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RE: comments on draft-ietf-ipsec-ciph-cbc-02.txt

Markku-Juhani Saarinen <mjos@ssh.fi> Fri, 13 March 1998 08:12 UTC

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Date: Fri, 13 Mar 1998 10:26:51 +0200
From: Markku-Juhani Saarinen <mjos@ssh.fi>
To: Roy Pereira <rpereira@TimeStep.com>
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Subject: RE: comments on draft-ietf-ipsec-ciph-cbc-02.txt
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> How many rounds do you suggest for IDEA?

IDEA has eight rounds.

4-round IDEA is a research toy, and should not even be called IDEA.
X. Lai and J. Massey never proposed it for real-life applications.

It apparently creeped into the drafts because Applied Cryptography
says (2nd ed, p. 325): 

  "(..) Currently the best attack against IDEA is faster than brute force
   only for 2.5 rounds or less; 4 round IDEA would be twice as fast and,
   as far as I know, just as secure."

This does not reflect our 1998 knowledge.

- mj

Markku-Juhani O. Saarinen <mjos@ssh.fi>, SSH Communications Security Ltd

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