Re: [PEN-TEST] OT - How secure is an ISDN line?

[Clem Colman <clem () colmancomm com>]

David,
> We have a number of ISDN connecting to other branch offices, ISP, etc.  Are
> data travelling on these ISDN lines secured/safe?  Can third party(ies)
> sniffed them?

There should be plenty of resources around about ISDN, but here's the quick rundown based on what I know of Australian 
implementations.  ISDN provides a connection based protocol allowing point to point connection by "dialing" the number 
of the point you wish to reach.

It is (was?) the building block of most telecommunications service in Australia, with most other services being 
delivered to the customer using ISDN.  A little known fact in Australia is that in many cases PSTN is converted to 
digital at the exchange and transmitted between exchanges over ISDN (only to be converted back to analogue at the other 
exchange to travel over the copper to the persons phone).

Can it be sniffed.  Certainly.  It's sequence is predictable and regular and no attempt is made to disguise traffic.  
Opportunities for interception, hard to know.  From the NTU over copper to the exchange obviously latent RF can be 
picked up, or a device simply planted in line.   Between exchanges it could cross a variety of other media, typically 
multiplexed with other channels, including fibre and microwave.

Think digital phone line.

Cheers,
Clem.