[TrunkCom] Re: Tetrapol in the US

[Ian Wraith]

Hi

>End To End Encrpytion?  What is that?

 OK with normal encrypted radio systems over here (Tetra & GSM) each radio
or phone has its own key. When a conversation is set up with another
radio the encrypted digital conversation is only between the radio and
the base station. The base station knows the radios encryption key
and decrypts the voice. This decrypted voice is then routed around the
network to the base station serving the 2nd radio or phone. This base
station knows that radios encryption key and re-encrypts the voice before
transmitting it. This has advantages in that key management is very
simple and radio users don't need to know the encryption key used by
the person they want to talk to. However if someone manages to tap the
lines between the base stations they can monitor everything. With end to
end encryption the base station doesn't decrypt the voice in fact it is
unable to as it doesn't know the key. So it just passes the encrypted
voice over the network to the next base station which transmits it. The
other radio can decrypt the voice as it knows the encryption key. This
method is much more secure but key management is awkward.

 Some radio systems use a mixture of methods. For instance Airwave the UK's
new Tetra digital radio system for the emergency services. Normal Police
use the first encryption system I mentioned so there aren't problems
if a Police car from one county goes into another. However some Police units
such as Special Branch (the anti-terror Police) use to end to end encryption
so even people who work at the Airwave base stations cannot listen to
what they are doing.

 Also you shouldn't confuse Tetra and Tetrapol both are digital radio
systems but the name is all that they have in common.

Regards

Ian