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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.crypt
Subject: Re: What is it really like?
Message-ID: <6682@utzoo.UUCP>
Date: Mon, 12-May-86 17:42:38 EDT
Article-I.D.: utzoo.6682
Posted: Mon May 12 17:42:38 1986
Date-Received: Mon, 12-May-86 17:42:38 EDT
References: <3264@reed.UUCP> <6650@utzoo.UUCP>, <507@ucsfcca.UUCP>
Organization: U of Toronto Zoology
Lines: 41

> >key-volume problems.  Where one needs skilled help is for things like
> >military field communications, where one-time pads are impractical.
> 
> Why are one time pads impractical in military field communications?
> If a CD ROM holds 500 megabytes of key in a drive like the ones that
> joggers are happy to wear on their belts,  I see no hard problems.

Because CD ROMs are the "leading edge" right now, i.e. they don't really
quite exist yet.  The military, like the phone company, has a lot of
built-in inertia in getting new technologies into service:  extensive
testing, mil-speccing, etc. eat up a lot of time.

There are also some other problems.  The requirement that one-time key
sequences never be re-used means you need a different key disk for each
communications link.  If you use different parts of the same disk, then
your whole communications system is compromised if the enemy captures
one of them -- something that must be assumed to happen occasionally.
Similarly, you must be prepared to issue new key disks at once if one
is captured.  In addition, if more than two stations use a single key
disk -- impossible to avoid, given the broadcast/multicast nature of a
lot of field communications -- they must all be kept in sync so they do
not re-use key text.  There are formidable problems of organization and
logistics here.  The system must be robust, capable of providing useful
communications despite chaos, confusion, repeated on-the-fly reorganization
of communicating groups, and deliberate attempts at disruption by clever
people on the other side.  Finally, the bulk of field messages have a
short useful lifetime; it really does not matter very much if the other
side can read them a month later.  One-time pads show fewer advantages
here than in more normal environments.

All this being true, it is nevertheless the case that my comments were
written with current technologies in mind.  Near-future technologies
like CD ROMs (if you think they are current technology, try to find
three companies that will sell compatible readers to you in quantity
ten thousand, *today*) will change things.  Personally I don't think
that one-time pads will filter all the way down to the lower levels of
field communication, but I would expect them to supersede a lot of the
current higher-level military cryptosystems.
-- 
Join STRAW: the Society To	Henry Spencer @ U of Toronto Zoology
Revile Ada Wholeheartedly	{allegra,ihnp4,decvax,pyramid}!utzoo!henry