New P25 Security Vulnerability Article

[escomm]

http://tech.slashdot.org/story/11/09/10 ... Encryption

At least one of the authors is a member here

[MattSR]

Interesting!

ADP and DES-OFB Key recovery via brute force..!

[d119]

Before anyone gets any bright ideas, please remember that tampering with encryption and trying to break it is a felony on a federal level.

Of course that is not the case when you are in a lab environment testing proof of concept, as was the situation with this article.

While it's not exactly step-by-step, this article does highlight a lot of the "how-to" and I certainly hope that one would be smarter than to attempt this.

I know MOST folks here have their heads screwed on properly, but history has shown us there are always one or two who think they are "exempt".

I'm not pointing any fingers or telling anyone what or what not to do, I just want to remind everyone that doing this sort of thing is not a good idea.

[Batwings21]

Come on you just know we are counting the days til someone with more brains than common sense cracks a local Pd's encryption and posts a feed on RR...

[mr.syntrx]

Or wants the PD to keep using the old key, so they keep replaying old OTAR frames with that key to make sure the PD does so

[MattSR]

It seems that in reality, no one really cares about people listening to encrypted comms. I mean, look how many times GSM A5/1 has been broken and I can't think of a single prosecution...

[escomm]

It seems that in reality, no one really cares about people listening to encrypted comms. I mean, look how many times GSM A5/1 has been broken and I can't think of a single prosecution...

Ah, that's the public getting spied on, nobody cares about that Spy on the government and a ton of bricks comes down on you.

Think of it this way, the average joe (in the US) has no expectation of privacy when in a public place, and therefore can be recorded by anyone with a camera. Now, an LEO in a public place still has no expectation of privacy... and yet some states still have laws on the books prohibiting this... and some prosecutors are dumb enough to pursue charges... and our current SCOTUS may be dumb enough to uphold the convictions...

[MattSR]

Thats very true Jeff - two different sets of rules..

If anyone is interested, here are the silence vectors that are the known plaintext which enables the keystream recovery and brute force attack:-

These are the 4 vectors are the start of the transmission and are the ones that are ideal for the RC4 stream cipher:-



And heres the two frames that are always at the end and are perfect for the DES-OFB key recovery (since OFB is a block chaining cipher it gives the two consecutive DES input and output blocks)



For those with a sharp eye, you will notice some trellis errors in there that were the result of a bug and a bad signal. This has now been fixed.

Cheers,
Matt

[com501]

Interesting.

This only works of course, if the user of the encrypted radio assumes his traffic is secure.....

Nice work, though.

I'm gonna work on this as a demo for the boss....