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Re: RC4 improvement idea
In article <[email protected]>,
<[email protected]> wrote:
> At 12:01 PM 4/5/96 -0500, Jack Mott wrote:
> >I got a paper from the cryptography technical report server
> >"http://www.itribe.net/CTRS/" about a weak class of RC4 keys.
>
> The report was bogus:
>
> For one key in 256, you can tell what eight bits of the state box are.
> For one key in 64000 you can tell what sixteen bits of the state box are,
> and so on and so forth.
>
> Such keys are not weak.
No, the report was right: the weak keys are real.
For one key in 256, you have a 13.6% chance of recovering 16 bits of
the original key.
On average, the work factor per key recovered is reduced by a factor
of 35 (i.e. the effective keylength is reduced by 5.1 bits) by using
this class of weak keys.
- quoting from the report
I've experimentally confirmed this effect myself. Andrew Roos did
some good work.
Take care,
-- Dave Wagner