NYC events and cell phones

[Peter Fairbrother]

> Angelos D. Keromytis wrote:
[...]
> Most of the day I was around 116 Street (Columbia U. campus), but at around
> 7pm I went to West 4 Street (they hadn't closed that part off yet), and the
> problem persisted.
> 
> Just to clarify -- the phone was working, but the encryption was off (I
> suppose
> that could be classified as "not working" :-)
> -Angelos

The A5/1 encryption used in GSM 'phones can be switched off easily, in fact
it is not switched on at all (A5/0) in some countries. There is also a
weakened version (A5/2). All GSM phones support all three modes. The type of
encryption used is determined by the base station.

It is possible that damage to basestations or volume of traffic may have
caused this failure. Possibly, the telco switched it off to maintain
service. Equally, the FBI/NSA etc may have switched it off, but I don't know
why they would bother - the encryption is only between the mobile and the
basestation, and they could pick up plaintalk there much more easily.

AFAIK the mode of encryption is irrelevant to locating 'phones.

If you have a multi-band 'phone, perhaps it was using a different band
(analogue, no encryption possible) because the 1.9GHz band wasn't working?
In view of the message snippet below it seems the most likely possibility:

> In message <20010916185623.A20618 at panix.com>, t byfield writes:
[..] 
>> however, a very limited sample did suggest that single-band (i.e.,
>> domestic) phones were working while, side by side, 'world' phones
>> weren't.

Incidently, even the A5/1 algorithm is supposedly not very secure against eg
LEAs, Corporations, or perhaps even a very dedicated amateur, though I have
no exact details to hand.

-- Peter Fairbrother






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