Army signals security & "Clansmen" series radios

[Owen Lewis]

----- Original Message -----
From: "Charles Lindsey" <chl@clw.cs.man.ac.uk>
To: <ukcrypto@maillist.ox.ac.uk>
Sent: 06 September 2000 14:39
Subject: Re: Army signals security & "Clansmen" series radios


> On Wed, 6 Sep 2000 11:50:49 +0100
> "Owen Lewis" <oml@eloka.demon.co.uk> said...
>
> > One of the interesting points to ponder is whether - and if not why
> > not - the diplomats and military have not seized upon the invention of
> > public key ciphers, now 30 years old, as the single, simple and secure
> > solution to replace other more complex and expensive cipher systems.
>
> I think the reason may be that public key systems are good for
> one-to-one and one-to-few communications (and I would be surprised
> if the military did not use them for that).

I think we can take it as a 'given' that military command structures are
almost entirely hierarchical and that they are closely adhered to. With that
given, then it is logical that the pattern of communication will largely
follow the command structure that it serves. Hence, a basic knowledge of the
military command structure(s - because there are actually many, overlaid)
will be a reliable indicator to at least some some of the communications
provision.

As you surmise, many of the communication networks are of the control and
outstations type, especially those low level tactical radio links which use
voice communication. However, especially for land forces, some voice
and most data links have, for many years, relied on area networks,
where user groups make broadband wireless attachments latch on to a matrix
of intercommunicating, mobile, communications switching, nodes. Within each
user group, there may be just a handful of discrete users or and many as a
hundred or so.

Does one allow each individual user of such a system to generate their own
PK pair, placing the public key on duplicated and mutually updating servers
at each communication node? Or should one better use cipher systems where
the traffic is bulk encrypted and within which one-to-one superencryption
can
be employed as may be thought necessary?

It seems to me that, in a system designed to function in a high risk
environment, there would be a number of serious disadvantages to the use of
PK systems. Among the salients point are:

        1. Due to battle casualties and other operational reasons there is
apt to be a high turnover of persons filling a particular appointment. As
far
as te command hierarchy is concerned, the person is nothing and the
appointment is everything. Thus, it would be logical to tie the PK's to
appointments rather than to persons. Either way, there will be many
unwanted complications where the use of  or further dissemination of
information risks serious impediment if a PK system is used.

        2. The actual structure of operational formations is always
classified infomation and the overall identification of appointment holders
with such formations is also classified. It therefore follows that the
content of all supposes military key servers would also be classified. If
such a server could be captured without alerting the rest of the network (by
no means impossible), the potential to create a short - term paralysing
confusion in the command and administrative structures would seem to be very
real and a serious weakness.

> But they are not a good
> solution to communications that have to be broadcast to many recipients
> (to all Her Majesty's ships, for example). OTOH, it was broadcast
> messages from the High Commands that made possible the wholesale
> interception of enigma traffic during the war.

One might consider the limits of analogy between public and military or
diplomatic broadcast systems. All have a many thousands of square miles of
blanket coverage but m&d systems are still always intended only for a
relatively small group of recipients. Cipher is the means by which
information transmitted by such means is reserved to intended recipients
only. In this, there is there is a direct analogy of purpose to the
enciphering of pay-tv, though the latter system may have a million
legitimate recipients whereas a military system might have a hundred or even
much less. Another important difference is that very few military broadcast
systems are likely to be satisfactory if the broadcast transmissions are
blind, as public broadcasts almost invariably are; rather they should
usually require that an enciphered receipt assure that reception has been
made by all the authorised parties or to identify which authorised parties
may either not have received the transmission or, even, may not still exist.

Patently, it is possible to use PK systems for diplomatic/military
communication functions. The question is, whether those systems have a
balance of advantage that should promote such use or whether the balance is
one of disadvantage. If, as I believe, the balance may be strongly one of
disadvantage, the hypothesised disadvantages perhaps provide a perspective
to help evaluate the suitability of  PK systems in other environments.
That's the game I was proposing, rather than to suggest that there is some
fatal flaw in the PK per se. If weaknesses there be, it seems to me that
these are for more likely to be found in either flawed or simply
inappropriate use.

The trouble is that the mass of PK users are simply not equipped to evaluate
these matters for themselves. Hence, the provision over the counter of
'strong cryptography' in a box at 9.99 is, in a particular sense, a deceit.
Fine, the buyer gets what he has paid for but - whatever the caveats in the
product documentation or the buzz in usenet-  what he so often thinks/wishes
to believe is that he is buying is pre-packaged worldclass security. And
that he usually does not  do.

Owen