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Monday, February 18, 2008

SIM card and Mobile

Peace be upon you

How are you guys? today I am going to talk deeper about the mobile security, I will take it from windows mobile side, because this what I have experience in, I am sure that there is similar in other mobile operating systems, first let us see this next picture,

This is image for smashed SIM card(I was done of it :D), here what is inside it, can u see the small chip, well it is real any SIM, has a very small processor with very small amount of memory, this cards called Smart cards, there is many many types of it, but let us get back to our point, SIM card is a type of smart cards that has processor and memory, for now it is OK, this thing has also something called Card OS, it is very small operating system, simply what it does is, it receive requests from the card reader, this card do the operation and reply back to the reader, the reader takes it and that's it, now what happens when Mobile starts up and try to have the signal from the mobile service provider, there is some kind authentication conversation must be done between the SIM and the Mobile network, what your device do is being a middle man, it takes result from SIM and give it to network, and take what network says and give it to Sim, that's cool for now.
The SIM card is divided into files, some files are protected and not readable by the reader, and some are password protected and some are open to be read with any kind of reader, I will try to add sample that explain all of that, here is some API's that may help any one to do SIM application related using windows mobile platform
To be continued
I hope that this post was informative and helpful.
Thanks for your time.
Ahmed Essam


Anonymous said...

Wow, Ma Shaa Allah, rabena yezeedak men 3elmo
i liked the article so much, now i understand the mobile is a midtire between the network and the sim, but i thought the sim is keeping small amount of information and the sim ID only, i heard in the past that u can remove the sim while talking on the phone ? i though that the mobile used the sim ID to initialize the Voice Call, and then no operation on the sim anymore u can remove it.

again, i thought if you can copy this memory area u can duplicate the card.

now i believe the internal smart-sim processor and os are for the security purpose, the reason they give a limited APIs to limit the operations.

thanks NEOz

Ahmed Essam said...

Peace be upon you smoke

Look, SIM card has memory and it is good enough to contain your phone book and SMS, also this SIM card hold the code of the application that run on the SIM card, also there is hidden space for the Card OS, the need of SMS, depend on the application that runs on the SIM, old days it was some kind of logical bug,
this logical bug is, When you start a call, you can remove the SIM card so, the mobile will work for while, but as far as I know, there is some kind of control channel that request things, for example,

if you are talking and moving from cell to other cell, this operation will need a control channel operations, if the mobile didn't find the SIM, you will have a nice message on the screen "Insert SIM"

I will try to provide more information with references to help anyone needs it

Thanks for your time

Thanks for your reply smoky ;)

Ahmed Essam