Chaining ciphers

[Tim May <tcmay@got.net>]

At 4:26 PM -0800 1/28/98, Jim Gillogly wrote:

>Doesn't seem terribly likely.  Typically ciphers will look strong until
>someone discovers a chink.  The chink will sometimes lead to a serious
>break, but not always, and not always quickly -- but at that point the
>cipher looks weak.  Your best chance at encrypting stuff that needs a
>long shelf life is with a cipher that's had a lot of analysis and
>plenty of intrinsic key, like 3DES.

Carl Ellison talks about his strategy for chaining several ciphers.

I'm surprised more emphasis isn't given to doing this. For example, suppose
one chains 3DES, Blowfish, MISTY, IDEA, and GHOST together (I haven't
checked Schneier on these, but you all presumably get the idea). Then if
any one of these ciphers is shown to be weak, the overall chain remains
strong. The overall chain is as strong as its strongest link, not its
weakest link.

I don't think 3DES is weak, but chaining-in additional ciphers can't hurt.
(Just a minor slowdown in encipherment speed, presumably not important for
some critical uses.)

-- Tim May

The Feds have shown their hand: they want a ban on domestic cryptography
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