Subject: Mobile Communication and Computing

Topic: Security Issue in mobile Computing

Difficulty: High

1. The SIM is the entity that contains the identity of the subscriber. When placed in a Mobile Equipment (ME), together they become a Mobile Station (MS) which may then register onto a GSM network.
2. The primary function of the SIM in conjunction with a GSM network is to authenticate the validity of an MS when accessing the network.
3. In addition it provides a means to authenticate the user and may also store other subscriber-related information or applications. Subscription entitlements are stored not in the SIM, but in the network.
4. If the SIM functionality is incorporated into a multi-application card, the GSM application may be used in other telecommunication applications.
5. In addition, SIMs is permitted to contain non-GSM functionality. In the case of multi-application cards
6. The SIM card contains a microcontroller with ROM, RAM and an NVM.
7. The ROM (4 to 6 kB) stores the programs implementing the A3 and A8 encryption algorithms.
8. The RAM is relatively small (around 256 bytes). The NVM contains user’s parameters like International Mobile Subscriber Identity (IMSI), Location Area Identifier (LAI), PIN associated to SIM, user’s authentication key Ki etc.
9. The SIM card communicates with the phone in the asynchronous serial mode in half-duplex transmission at the data rate equal to 3.2 kbps in each direction.
10. The SIM card is portable i.e. it can be moved from phone to phone and still function in the same manner.