SIM card

A Subscriber Identity Module (SIM) is a removable smart card for mobile phones. SIM cards securely store the service-subscriber key used to identify a mobile phone. 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.

The use of SIM cards is mandatory in the GSM world. The equivalent of a SIM in UMTS is called the Universal Integrated Circuit Card (UICC), whereas the Removable User Identity Module (RUIM) is more popular in CDMA phones.

SIM cards are available in two standard sizes. The first is the size of a credit card (85.60 mm × 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.

W-SIM is a SIM card which also integrates core cellular technology into the card itself.

GSM 11.11 - Specification of the Subscriber Identity Module - Mobile Equipment (SIM - ME) interface. GSM 11.14 - Specification of the SIM Application Toolkit for the Subscriber Identity Module - Mobile Equipment (SIM - ME) interface

Memory storage size

The typical low cost SIM card (GSM 11.11 only) has little memory, 2–3 KB as described in GSM 11.11 (telephone directory and so on). Such data storage is used by the phone directly. The market segment of low cost SIM is constantly shrinking.

SIMs with additional applications (GSM11.14) are available in many storage sizes, the largest being the 1 GiB SIM. Smaller sized SIMs such as the 32 KB and 16 KB are the most prevalent in areas with less-developed GSM networks. There are also Large Memory SIMs, on the order of 128–1024 megabytes.

SIM card memory will vary across mobile carriers.

At the end of 2006 the most common GSM SIM in the US is 64 KB - this stemmed from Nov 2004 when the Cingular and AT&T merger triggered the supply of 64 KB SIMs over 32 KB to better support both networks (and make them look like one).

Operating systems

SIM operating systems come in two main flavors: Native and Java Card. Native SIMs are based on proprietary, vendor specific software whereas the Java Card SIMs are based on standards, particularly Java Card which is a subset of the Java programming language specifically targetted for small embedded devices. Java Card allows the SIM to contain programs that are hardware independent and interoperable.

Data

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). 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), and Value Added Service (VAS) applications. (look to GSM 11.11)

ICCID

Each SIM is internationally identified by its ICC-ID (International Circuit Card ID). ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization.

IMSI

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 16 byte 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.

Authentication process

On mobile startup the SIM sends its IMSI to the Mobile Operator requesting access and authentication.
The operator network searches its database for the incoming IMSI and its associated Ki.
The operator network then generates a Random Number (RAND) and signs it with the SIM’s Ki computing another number known as Signed Response (SRES_1)
The operator network then sends the RAND to the SIM card that also signs it with its Ki and sends the result (SRES_2) back to the operator network.
The operator network then compares its computed SRES_1 with the SIMs computed SRES_2. If the two numbers match the SIM is authenticated and granted access to the operator's network.

The GSM "crypto" algorithm for computing SRES_2 has a weak point, however, which allows the extraction of the Ki from a SIM card and the making of a duplicate SIM card.

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.

Japan

Japan's PDC system also specifies a SIM, but this has never been implemented commercially. The specification of the interface between the Mobile Equipment and the SIM is given in the RCR STD-27 annex 4. The Subscriber Identity Module Expert Group was a committee of specialists assembled by the European Telecommunications Standards Institute (ETSI) to draw up the specifications (GSM 11.11) for interfacing between smart cards and mobile telephones. In 1994, the name SIMEG was changed to SMG9.

Finland

In July 2005, the Finnish government announced that a Citizen Certificate - a government-guaranteed 'electronic identity' included in a SIM card - would be made available to every individual resident in Finland before the end of 2005, allowing mobile phone users to access e-services on the move. The Citizen Certificate has been described as "basically an e-ID card that will be compatible with several hardware devices, such as mobile phones, PDAs, personal computers, Digital TV sets, and public web kiosks". [1]

External Links

SIM Card Phone