(fwd) Re: NSA Helped Yeltsin Foil 1991 Coup

[Eli Brandt]

> From: "Perry E. Metzger" <perry at imsi.com>
> > If you suspect that some of the non DOD/NSA cyphers might be broken,
> > but you are not ready to employ one-time-pads, then you should
> > threshold you mesages into N parts so that all N are needed to recover
> > the original.  Then encrypt each part under a different cypher.
> 
> Its far simpler to encrypt your message with multiple systems, one
> after another, than to break it up in the manner you suggest, and the
> security is in fact better that way than in the manner you suggest.

Why?  If you XOR-split the message and encrypt each mask differently,
you are /guaranteed/ that all of the encryption methods must be
broken to retrieve the original.  If you use repeated encryption,
this is much harder to prove, and not always true.  There's a result
that if you choose the first cipher unwisely, you're hosed no matter
what you do on top of it.

   Eli   ebrandt at hmc.edu