Is GSM a blackbox in OpenMoko
Torsten Schlabach
tschlabach at gmx.net
Fri Dec 14 16:04:35 CET 2007
Dear Nikolaus!
(Please remember to cc: the list. This list isn't configured with a
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> It is called Certification or Approval.
I see. In Germany AFAIK this is the Bundesnetzagentur, formerly known as
RegPT (Regulierungsbehörde für Post und Telekommunikation, just for the
non Germans on this list). And I know that each country has a similar
authority, which is in charge or regulating and licensing the use of
radio spectrum as well as making sure that devices which use radio
frequencies do not cause other users any trouble, etc.
Nevertheless, I think we are mixing up some things here, IMO. But prior
to explaining what I mean, just let me clarify one thing:
> In Germany we have a constitution which simply disallows tapping any
> phone calls (except under certain specific exceptions).
I did not write anything about tapping phone calls at all and this is by
no means what I intend to do.
> So, the Government has got the task by democratic elections to
> implement means so that this is guaranteed for everyone who uses a
> phone system.
I agree that the Government has to make laws that forbit tapping of
phone calls, but I seriously doubt that the Government is in charge of
implementing technical means to prevent that. I am for example to at all
aware of any legislation that would require each VoIP call to be
encrypted. Theoretically what you say would mean a ban of analoge phones
as tapping them is damn easy. But that's not the subject of this discussion.
> And since the SIM card plays a crucial role in that, it is simply not
> possible to access the SIM card directly by software. No manufacturer
> in this world can change that.
I doubt this is acurate. For two reasons:
1. It is not a problem to access the SIM card via software. Buy a
standard card reader for 20 EUR, buy a book like this:
http://www.amazon.de/Handbuch-Chipkarten-Aufbau-Funktionsweise-Einsatz/dp/3446220364/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1197643283&sr=8-1
and there you go.
You can easily do things such as reading the contacts on the SIM card,
change the order of preferred networks, even change the PIN *if you know
the current PIN*. You cannot do anything illegal that way, no doubt. You
will for example not be able to crack the PIN of a SIM card you don't own.
I am not the 150% expert but I understand that the SIM card is a
standard Smartcard (it has a processor, i.e. it is a computer) with a
specific piece of software. It has a secret cryptographic key stored
which it will never reveal to the outside. After you have logged into
the card using the PIN number, the SIM card will issue a session key to
the GSM modem (I think this is called IMSI) which it will use to
authenticate to the GSM network. So this is some kind of shared secret
mechanisn, i.e. your HLR (home location register) run by your GSM
network operator knows the key that's on your SIM card and thus can
verify that the device which attempts to book into the net is in
possession of the SIM card.
Speaking practically:
One hot application these days is dual-SIM phones. Many people have
several SIM cards these days to use in different networks for various
reasons, but there's nothing wrong with that I think. But people don't
necessary want to carry 2,3 or more phones.
There is for example somthing in Bluetooth called "SIM access profile"
which is a mean to share a SIM card over Bluetooth. This is used by some
built-in car phones (not to mix up with simple hands-free sets, which
just transmit the audio over the Bluetooth connection) which read the
SIM card of the mobile in your pocket when you enter the car.
I was looking at implementing whatever mechanism where I could host a
SIM card that I legally own on a server and communicate with that SIM
card over whatever network connection (WiFi if available, maybe UMTS,
Bluetooth, ...).
But as I cannot hook the communication between the GSM modem and the SIM
card (which is some kind of serial line connection) I have no means of
doing that.
What made me think I would?
Well, would it be entirely impossible to think of a chipcard reader and
a GSM modem as independent devices which are wired together via
software, i.e. some kind of pipe? And I doubt that a GSM modem with such
a kind of "external" chipcard reader would not get FCC or whatever approval.
Any finally, is it part of the FCC approval for the Texas Instruments
GSM modem that they are not allowed to make their specs public or is it
more TI not wanting to do that for pure commercial reaons.
In the latter case, this is heavil against the idea of "free your phone"
and having an *open" platform.
And you should never implement security by obscurity, as Kerckhoffs'
principle suggests:
> a cryptosystem should be secure even if everything about the system,
> except the key, is public knowledge
Sorry for the long email, but I think we're touching a very important
subject here for the success of OpenMoko / Neo 1973 ff.
As you will know from media, there's tons of other groups who are
promoting some kind of open operating system for phones, such as Google
and the Linux Phone Standard Forums (LiPS, http://www.lipsforum.org/).
I thought (I hoped) that OpenMoko is different in that I have control
over the *whole* phone, not just on the UI / application layer.
Regards,
Torsten
Dr. H. Nikolaus Schaller schrieb:
>
> Am 14.12.2007 um 14:06 schrieb Torsten Schlabach:
>
>> > This would be correct, and the only way many (most?) national
>> > governments would have it.
>>
>> What has the government to do with that?
>
>
> It is called Certification or Approval. Government (e.g. FCC) is
> generally in all countries responsible for allocation of radio
> frequencies. And what is allowed and what not. Think of it like streets
> where there are traffic rules and not all cars and vehicles may use any
> road. And, you need a driving license.
>
> Not always Government handles this directly (any more). They have
> delegated that to public institutions. Or even to large manufacturers.
> But those are under control and certifications - and don't want to risk
> any problems. Therefore, they provide details only under NDA.
>
>> > It would be a gross understatement
>>
>> Well, I mean for the purpose of using the GSM network. No doubt about
>> any kind of other uses, but this setup precludes you from doing
>> things like:
>>
>> - implement a SIM card in software
>> - utilize a different SIM card which you have access to via a network
>> - many other potentially interesting things
>>
>> I need to say, I was hoping that I could get closer to the RAC (radio
>> access) layer with OpenMoko.
>
>
> What did you make you think that you could legally expect that?
>
> I think you should buy a good book about how GSM works and protocols.
> Most of these things are public. Except some details how the SIM card
> and the hardware interacts for encryption and privacy.
>
> Coming back to what Government has to do with that.
>
> In Germany we have a constitution which simply disallows tapping any
> phone calls (except under certain specific exceptions). So, the
> Government has got the task by democratic elections to implement means
> so that this is guaranteed for everyone who uses a phone system. And
> since the SIM card plays a crucial role in that, it is simply not
> possible to access the SIM card directly by software. No manufacturer
> in this world can change that.
>
> Nikolaus Schaller
>
>
>
>
>
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