Re: "Alien" cryptanalysis

From: Douglas A. Gwyn (DAGwyn_at_null.net)
Date: 05/19/03 

Date: Mon, 19 May 2003 17:01:41 -0400

JohnTromaville wrote:
> I thought the attack was on a reduced version of SKIPJACK?

That's right.

>Tom St. Denis wrote:
>>They picked 32 rounds because they thought that no
>>attack would approach that many.

That was nonsense. The number of rounds is an aspect
of the encryptor, not necessarily of a method of attack.
The reason 32 rounds were picked is that that many rounds
were necessary to forestall attacks (such as the one
Biham pursued).

> just curious on this one - how does one choose the
> number of rounds when designing a crypto?

There is no simple answer to that, and so far as I am
aware no correct, general methodology for such things
available in the academic community.

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