Batboard

Good afternoon group

Hopefully someone can help me on this one. Our state police are about to invest in a P25 system and there is talk that it will be fully encrypted all the time. Damn !

Anyway, there is also talk that it will be a Conventional system and NOT a trunked system.

Does OTAR work on a Non Trunked System ? I was under the impression (and I may very well be wrong here folks) that it works only on a trunk system and the OTAR commands are fed as a part of the control channel stream.

Ie: on a conventional system does the normal channel open up and spit out a heap of digital signals to change keys etc etc if it does work on a conventional system ?

If it doesn't work on a conventional system, I can envisage problems when radios are lost/stolen etc etc in having keys changed ! After all an encryption system is only as secure as the keys and key rotations it is using..

Any thoughts appreciated
Thanks
Mike

Otar can work on conventional systems.

If a radio is lost or stolen, a command can be sent from the radio system to "kill" the radio so that it does not function. This would apply to trunked to conventional systems if the option is purchased.

The radio's themselves can be programed to erase the encyption key if the battery is removed or if a password is entered incorrectly. There is no known way to retrive the encyption key from the radio.

I believe USMS runs a system that does OTAR... It's straight up conventional, and I think all Astro.

-Alex

Pj wrote:Otar can work on conventional systems.

If a radio is lost or stolen, a command can be sent from the radio system to "kill" the radio so that it does not function. This would apply to trunked to conventional systems if the option is purchased.
.

OK on that so it will work on a conventional system.

Now the other part of my question

Ie: on a conventional system does the normal channel open up and spit out a heap of digital signals to change keys etc etc

In the case where an inner city channel may be running say 500 units and they want to change the encryption key, how is that achieved (is it as I describe above ?

Then, what happens if the unit is on another channel when the OTAR command is sent out, does the despatcher (or whoever) then have to send out the commands over and over again until everyone is back on air with the new key ?

If I am way off in grasping how this will work on a conventional channel, please enlighten me

Thanks
Mike

G'day... I'll address these from the beginning as I ran out of time to reply yesterday

mrtor wrote:Hopefully someone can help me on this one. Our state police are about to invest in a P25 system and there is talk that it will be fully encrypted all the time. Damn !

Welcome to the way SA and NSW have been doing it for a while (ok, maybe 12 months) now

Not too sure about NSW, but I know that SA has a P25 trunking network, and the police are using encrypted Astro digital voice.

Anyway, there is also talk that it will be a Conventional system and NOT a trunked system.

P25 generally refers to trunking. Are you saying that it's likely just conventional with encrypted IMBE (Astro) digital voice?

Does OTAR work on a Non Trunked System ? I was under the impression (and I may very well be wrong here folks) that it works only on a trunk system and the OTAR commands are fed as a part of the control channel stream.

Yes, OTAR works on conventional channels as well as trunking. MDC has OTAR capability for when Astro is not in use (ie encrypted non-digital voice), as does Astro itself. OTAR isn't actually part of the trunking control channel.

Ie: on a conventional system does the normal channel open up and spit out a heap of digital signals to change keys etc etc if it does work on a conventional system ?

Basically

If it doesn't work on a conventional system, I can envisage problems when radios are lost/stolen etc etc in having keys changed ! After all an encryption system is only as secure as the keys and key rotations it is using..

Correct. But there are plenty of tamper protection mechanisms that Motorola have engineered that if enabled make it very hard to capture and extract keys intact.

mrtor wrote:In the case where an inner city channel may be running say 500 units and they want to change the encryption key, how is that achieved (is it as I describe above ?

Then, what happens if the unit is on another channel when the OTAR command is sent out, does the despatcher (or whoever) then have to send out the commands over and over again until everyone is back on air with the new key ?

Pretty much... They'll either get rekeyed back at base with a KVL (handheld device that plugs directly into the radio), or they'll get the dispatcher to remotely rekey the radio when they realise that they keep getting decryption error messages on the radio.

If memory serves...each radio in an OTAR system is initially loaded with what's called a shadow key. Its this key that allows the OTAR to work. The dispatcher can rekey the radio or the radio user can send a command from his radio to request a reload/new key. When the request is sent, the OTAR computer verifies if that is the proper radio and if that radio is still authorized for a new key.

Because of the shadow key and other safeguards, you cannot buy the same radio with the same options and have that radio properly OTAR.

And to clarify, the encryption key used for OTAR that Pj has mentioned, is only used for OTAR. This reduces the traffic over the air using this key meaning that you'll need a LOT (years and years) of OTAR requests before you can get enough traffic to even start thinking about deriving the key and being able to listen to the new keys as they're being broadcast.

I don't think that counts r0f