Trei, Peter wrote:
Why the heck would a government agency have to break the GSM encryption
at all? The encryption is only on the airlink,
> and all GSM calls travel through the POTS land line system in the clear,
> where they are subject to warranted wiretaps.
Breaking GSM is only of useful if you have no access to the landline
portion of the system.

Some governments are more concerned about using warrants than others are. Sometimes the ones that are concerned about them also have police agencies that like to avoid using them. Some phone companies are pickier about paperwork than others. Some phone companies are faster about responding than others. Having governments that are officially less concerned about warrants is often correlated with having monopoly phone companies, which is often correlated with slow bureaucratic response - they may be extremely happy to help out the police, but that doesn't mean it doesn't take 18 steps to accomplish it.

Landline-based wiretaps work best if you know the phone number;
over-the-air systems can be more flexible about picking up
any phone nearby, so if you see your target pick up a phone,
but don't know its phone number, they're more convenient.
And in landline-tapping environments, clever law-evaders
can usually acquire the equipment to keep switching phones.



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