28-01-2011, 02:15 PM
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ABSTRACT
A SIM (subscriber Identity Module) is a removable smart card for mobile phones. It contains subscriber information, such as the IMSI (International Mobile Subscriber Identity). It can also be used to store user-defined information such as phonebook entries.
The use of SIM card is mandatory in GSM world. There are two types of SIM operating system – Native and Java card. The SIM card is activated in an environment using five stage process called, authentication process.
INTRODUCTION
The Subscriber Identity Module (SIM) is a small smart card which contains both programming and information. The A3 and A8 algorithms are implemented in the Subscriber Identity Module (SIM). Subscriber information, such as the IMSI (International Mobile Subscriber Identity), is stored in the Subscriber Identity Module (SIM). The Subscriber Identity Module (SIM) can be used to store user-defined information such as phonebook entries.
One of the advantages of the GSM architecture is that the SIM may be moved from one Mobile Station to another. This makes upgrades very simple for the GSM telephone user.
MAIN FEATURES
1. Importance
SIM card is a mandatory in the GSM world.SIM card is the basic component of GSM mobiles. They act as an interface between the handset and the connectivity. It gives an unique identification to each devices both internally and externally. Nowadays they have been added with more data storage capacity.
2. Installation
The SIM card allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another mobile phone.
3. Cost & Memory
The typical low cost SIM card has little memory, 2-3 KB as described. Such data storage is used by the phone directly. This memory may not be sufficient nowadays. The market segment of low cost SIM is falling down.
There are also Large Memory SIMs, on the order of 128-1024 megabytes.Because of the insufficient memory, new market comes with large memory. In future we can expect SIM cards having megabytes of capacity.
4. Types
SIM cards are available in two standard sizes:
The first is the size of a credit card(85.60 mm x 53.98 mm x 0.76 mm)
The newer, more popular miniature-version has a width of 25 mm, a height of 15 mm and a thickness of 0.76 mm.
OPERATING SYSTEM
SIM operating systems come in two main types: Native and Java Card.
1. Native SIMs:
Native SIMs are based on proprietary, vendor specific software .
A native sim is fixed and cant be replaced by other vendors SIM. It cant be used in other vendors cellphone also. It is designed for a particular hardware type.
2.. Java Card :
Java Card SIMs are based on standards, particularly Java
Card which is a subset of the Java programming language specifically targeted for small embedded devices.Java Card allows the SIM to contain programs that are hardware independent .
DATA ON SIM
SIM cards store network specific information used to authenticate and identify subscribers on the Network, the most important of these are the ICCID, IMSI, Authentication Key (Ki), Local Area Identity (LAI) and Operator-Specific Emergency Number.
The SIM also stores other carrier specific data such as the SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN), Advice-Of-Charge parameters and Value Added Service (VAS) applications.
ICC-ID (Integrated Circuit Card - ID)
Each SIM is Internationally identified by its ICC-ID. ICC-IDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization.
IMSI( International Mobile Subscriber Identity)
SIM cards are identified on their individual operator networks by holding a unique International Mobile Subscriber Identity. Mobile operators connect mobile phone calls and communicate with their market SIM cards using their IMSI.
Authentication key (Ki)
The Ki is a 128-bit value used in authenticating the SIMs on the mobile network. Each SIM holds a unique Ki assigned to it by the operator during the personalization process. The Ki is also stored on a database (known as Home Location Register or HLR) on the carrier’s network.
The SIM card is designed so that the Ki cannot be obtained using the smart-card interface. Instead, the SIM card provides a function, "RUN GSM ALGORITHM", that allows the phone to pass data to the SIM card to be signed with the Ki. This, by design, makes usage of the SIM card mandatory unless the Ki can be extracted from the SIM card, or the carrier is willing to reveal the Ki. In practice, the GSM "crypto" algorithm for computing SRES_2 from the Ki has a weak point. This allows the extraction of the Ki from a SIM card and the making of a duplicate SIM card.
Authentication process
1. When the Mobile Equipment starts up, it obtains the IMSI from the SIM card, and passes this to the mobile operator requesting access and authentication. The Mobile Equipment may have to pass a PIN to the SIM card before the SIM card will reveal this information
2. The operator network searches its database for the incoming IMSI and its associated Ki.
3. The operator network then generates a Random Number (RAND) and signs it with the Ki associated with the IMSI (and stored on the SIM card), computing another number known as Signed Response (SRES_1).
4. The operator network then sends the RAND to the Mobile Equipment, which passes it to the SIM card. The SIM card signs it with its Ki, producing SRES_2 which it gives to the Mobile Equipment along with encryption key Kc. The Mobile Equipment passes SRES_2 on to the operator network.
5. The operator network then compares its computed SRES_1 with the computed SRES_2 that the Mobile Equipment returned. If the two numbers match the SIM is authenticated and the Mobile Equipment granted access to the operator's network. Kc is used to encrypt all further communications between the Mobile Equipment and the network.
Location area identity
The SIM stores network state information which is broadcast to it from the network, such as the Location Area Identity (LAI). Operator networks are divided into Location Areas, each having a unique LAI number. When the Mobile changes its location from one Location Area to another it stores its new LAI in SIM and sends it to the operator network to inform network with its new location. If the handset is turned off and back on again it will take data off the SIM and search for the LAI it was in. This saves time by avoiding having to search the whole list of frequencies that the telephone normally would.
UNIVERSAL SUBSCRIBER IDENTITY MODULE
It is an application for UMTS mobile telephony running on a UICC smart card which is inserted in a 3G mobile phone. There is a common misconception to call the UICC card itself a USIM, but the USIM is merely a logical entity on the physical card.
It stores user subscriber information, authentication information and provides storage space for text messages and phone book contacts. The phone book on a UICC has been greatly enhanced.
For authentication purposes, the USIM stores a long-term preshared secret key K, which is shared with the Authentication Center (AuC) in the network. The USIM also verifies a sequence number that must be within a range using a window mechanism to avoid replay attacks.
CONCLUSION
SIM is a smart card which forms an unavoidable part in GSM mobile phones. It stores several user-defined information such as phonebook entries and other subscriber information like IMSI. SIM may be moved from one Mobile Station to another which forms an advantage for the GSM architecture. This makes upgrades very simple for the GSM telephone user.
