Re: [SG2] APFCs in Stargrunt

On Wed, 16 Dec 1998, Adrian Johnson wrote:
> <snip>
> >  Makes using captured equipment difficult in the extreme,
> >protects sensitive data (The divisional commander and his staff is
dead,
> >your commandos power up the Divisional AI Mainframe. . . it asks for
an
> >IFF reading anywhere in the vicinity, finds nothing, and formats the
> >hard drives), and oh-by-the-way, keeps your grunts from being
shredded
> >by APFCs.  It only recieves and responds to IFF interrogations from
> >friendly equipment, not a continuous transmission, so your guys can't
be
> >tracked by their little brain beacons.
> 
> What happens when the other guy figures out the frequency / code to
your
> implants and mimics the IFF interrogation signal - revealing all your
> troops OR creating boobytraps / mines that use your IFF to trigger,
etc etc
> etc.

use very strong cryptography! i can't resist looking at the details of
the
crypto here. sorry.

<geek:crypto>

the system would use an asymmetric cipher (aka a public/private-key
system, like the RSA cipher used in PGP, etc). basically, the messages
encrypted with the public key can only be decrypted with the private key
and vice versa.

the IFF scanner sends out an interrogation ping, including its own id, a
challenge sequence (different every time) and the challenge sequence
encrypted with its own private key. since all IFF units have a registry
of
all public keys, this allows the IFF tag to verify that the IFF scanner
is
really on its side. the tag responds with a message consisting of its
own
id and the challenge string encrypted with the tag's private key. this
allows the scanner to verify that the tag is who it says it is. the
tag's
reply is encrypted with the scanner's public key, so that only the
scanner
can read it.

thus, before an IFF tag says anything, it makes sure the scanner is
legitimate, and not an enemy EW unit. security is provide by using very
long cipher keys.

for bonus security, the challenge sequence would include a timestamp, to
protect against 'playback' attacks where the enemy records  an IFF
challenge and plays it back to stimulate and IFF tag. all IFF units
would
need synchronised time - this can be got from the GPS system. also, the
scanner's id should be attached to the tag's message, so that multiple
simultaneous scans do not interfere.

</geek:crypto>

> Would yours "turn off" if the "carrier" dies?  If they did, you
wouldn't be
> able to use them as easily for identification of casualties.	If they
> didn't, my commandos would be hacking off the heads of your divisional
> commander and staff to use as access keys to the mainframe...

the message would include info on the wearer - whether he is alive or
dead, for instance. the mainframe's security manager would not allow
access by dead users.

the thing with IFF is that, unless your tag has a directional emitter,
the
enemy will be able to pick up the replies your tag makes to scans. if
these are infrequent (eg only when a scanner notices a new potential
target), or if the reply is made with low-frequency frequency-agile
radio,
etc, then it is not too bad.

Tom