Re: Missiles in Space Combat?

Eivind <eivindorama@xxxxxxxxx> wrote:

Derek Lyons skreiv:

Not just a stock of pads, but the keying schedule (I.E. when to use
which pad) as well. A somewhat thorny logistics problem but one long
solved in principle and largely in practice.

But OTPs are icky. They're fundamentally unbreakable mathemathically,
there is that. But they have a couple of annoying problems;

1) The "key" (pad) needs to be as large as the sum-total of all messages
you want to send before re-keying.

That was a problem previously. With the ability to store terabytes in
a relatively small volume, that problem goes away. Also keep in mind
that military practices (quite strenuously) minimizing message length.

2) The pads must be securely distributed to all participants beforehand,
and updated as they run out. Which -isn't- the case with say PK-crypto
(though you -do- need to distribute a trusted public-key to all
participants, this must however only be tamper-proof, not secret, so a
lot easier, you can distribute a public-key by printing it in the NYT
for that matter)

As I said above, this is a thorny problem but one long solved in
principle and largely in practice.

3) If you've got more than 2 participants, then either EVERYONE is
fucked when -1- participant is somehow compromised (or makes a mistake
in using his pad), or you need one pad for every party you could
potentially want to communicate with, which becomes impractical rather
quickly.

That's less of a problem than you might think. First off, because the
folks that need to talk to lots of folks are typically at HQ, which
has lots of room to store keying material. Second off, fleet units
communicating with each other only need to keep their communications
secret for a fairly brief time. (And they generally aren't sending
the stuff you Really Really want to keep a secret for a Very Long Time
anyhow.)

In practice, conventional crypto with a pre-shared-key is equally
secure, in the sense that the math in the crypto is very VERY unlikely
to be the weakest link in your security.

In practice, PK-crypto is also equally secure, and a hell of a lot more
practical due to the fact that public-keys do not need to be secret.

In practice however PK-crypto has a significant weakness - once it's
cracked, the whole ball of wax is cracked. The message you sent using
a given key ten years ago as well as the message you sent using that
key ten minutes ago. There's a reason why professional organizations
rotate keys on a regular basis.

D.
--
Touch-twice life. Eat. Drink. Laugh.

http://derekl1963.livejournal.com/

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
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