At 03:50 PM 6/3/03 -0700, Eric Blossom wrote:
GSM and CDMA phones come with the crypto enabled.  The crypto's good
enough to keep out your neighbor (unless he's one of us) but if you're
that paranoid, you should opt for the end-to-end solution.  The CDMA
stuff (IS-95) is pretty broken: *linear* crypto function, takes 1
second worst case to gather data sufficient to solve 42 equations in
42 unknowns, but again, what's your threat model?  Big brother and
company are going to get you at the base station...

Big brother has a limited budget, just like the rest of us. If he has to produce a warrant or tap a wire somewhere to listen in on me, he probably won't bother.

The only thing protecting my cellphone calls right now is trivially-broken encryption, the need for some moderately expensive equipment, and some laws prohibiting cellphone eavesdropping. That means that some bad guys may be eavesdropping now, and there's no telling how many bad guys will be doing so tomorrow. Nobody here knows how much eavesdropping is being done, because communications intercepts can be done without leaving any record anywhere. Do the police in some cities troll for interesting cellphone calls? Does the NSA do that in the US, quietly? Do Russian or French intelligence agencies? How would we know?

So, what can I do about it, as an individual? Make the cellphone companies build good crypto into their systems? Any ideas how to do that?

The only way I can see getting decent security on my cellphone is to do something that doesn't require the rest of the world's permission or assistance. The simplest version of that is to have a box at my house that's connected to two phone lines, and have all calls to and from my cellphone go through that box. Calls to other secure cellphones can be encrypted end-to-end. Calls to everyone else get encrypted between my phone and my box at home. I spend a little extra for extra security, nobody else has to pay anything, and I can call friends on my cellphone without being susceptible to trivial eavesdropping.

Can the bad guys defeat this? Sure, they can tap my landline, or bug my car, or do all sorts of other things. But none of those are cheap enough to do to everyone, and probably none are cheap enough to do to me. Tapping my landline either means interacting with the phone company, or paying someone to go install a tap, each of which implies a risk of getting caught, practical limits on how often it can be done, etc.

This also bypasses the "network effect" of encrypting phones, where you get approximately zero benefit from having one until they're widespread. I have an old Comsec 3DES phone at home. It's nice technology. I think I've used it twice. If you're not a cryptographer or a cocaine smuggler, you probably don't know anyone who owns an encrypting phone or would particularly want to. Even if you'd like to improve your own privacy, you can't buy an end-to-end encrypting phone and improve it much. That's what I'd like to see change.


--John Kelsey, [EMAIL PROTECTED] PGP: FA48 3237 9AD5 30AC EEDD BBC8 2A80 6948 4CAA F259

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