Subscriber Identity Module

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It has been suggested that Virtual sim be merged into this article or section. (Discuss)

“Card holder” redirects here. For other uses of the word, see card enclosure.

An AT&T Mobility mini SIM card.

A mini SIM card next to its electrical contacts in a Nokia 6233.

A Subscriber Identity Module (SIM) is a removable smart card for mobile cellular telephony devices such as mobile computers and mobile phones. SIM cards securely store the service-subscriber key (IMSI) used to identify a GSM subscriber. 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 or broadband telephony device.

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 devices.

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.

The First SIM Card made in 1991, Munich smart card maker Giesecke & Devrient sold the first 300 SIM cards to Finnish wireless network operator Elisa (ex. Radiolinja).

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

1 Computer Integration
2 Memory storage size
3 Operating systems
4 Data
5 Japan
6 Finland
7 References
8 See also

[edit] Computer Integration

The SIM card is optional depending on the type of WWAN (Mobile Broadband) card that is installed in a laptop, such as the Dell Latitude D830, or other capable device.

[edit] 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).

[edit] Operating systems

SIM operating systems come in two main types: 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 targeted for small embedded devices. Java Card allows the SIM to contain programs that are hardware independent and interoperable.

[edit] 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) 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. (look to GSM 11.11)

[edit] ICCID

Each SIM is Internationally identified by its ICC-ID (Integrated 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.

[edit] 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.

[edit] 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.

[edit] Authentication process

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.
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 Ki associated with the IMSI (and stored on the SIM card), computing another number known as Signed Response (SRES_1).
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.
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.

[edit] Location area identity

The SIM stores network state information, which is received from the Location Area Identity (LAI). Operator networks are divided into Location Areas, each having a unique LAI number. When the device changes locations, it stores the new LAI to the SIM and sends it back to the operator network with its new location. If the device is power cycled, it will take data off the SIM, and search for the previous LAI. This saves time by avoiding having to search the whole list of frequencies that the telephone normally would.

[edit] 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.

[edit] 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".It is based on open standards and secured Public Key Infrastructure (PKI) [1]

[edit] References

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
[2] Installing the SIM Card, Dell Latitude D830 Service Manual (documentation)