Army signals security & "Clansmen" series radios

[Dave Bird]

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In article <200009061339.OAA17295@clw.cs.man.ac.uk>, Charles Lindsey
<chl@clw.cs.man.ac.uk> writes
>       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). 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).

 That is almost a despair situation for security: there are so many
 message terminals that someone is bound to get careless through 
 sheer numbers.

 Where the medium allows it, it is best to send individual variant
 messages to each local key.


 If they lose control of a receiving key then someone can receive as
 that node until you find out and kick them off, possibly because you
 marked the message with variant information --- where the content is
 unusable unless one can show an intact digital sig, it is a bit of a
 give-away that the signed text includes recipient name.

 Likewise a transmitting key, when they fail to give their confirmation
 phrase or something.


 The one thing you can't safeguard well is plaintext, since it relies
 on the INTERSECTION of their individual securities: for the time
 during which at least one node is compromised, plaintext leaks out.


 In short, confidence in the security of a broadcasted (narrowcasted?) 
 message goes down rapidly as the number of recipients increases.


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