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A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that securely stores the international mobile subscriber identity (IMSI) and the related key used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers).
A SIM circuit is embedded into a removable plastic card. This plastic card is called a "SIM card" and can be transferred between different mobile devices. A SIM card follows certain smart card standards. SIM cards were first made the same size as a credit card (85.60 mm × 53.98 mm × 0.76 mm). The development of physically smaller mobile devices prompted the development of smaller SIM cards where the quantity of card surrounding the integrated circuit is reduced.
A SIM card contains its unique serial number (ICCID), international mobile subscriber identity (IMSI), security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to and two passwords: a personal identification number (PIN) for ordinary use and a personal unblocking code (PUK) for PIN unlocking.
The SIM was initially specified by the European Telecommunications Standards Institute in the specification with the number TS 11.11. This specification describes the physical and logical behaviour of the SIM. With the development of UMTS the specification work was partially transferred to 3GPP. 3GPP is now responsible for the further development of applications like SIM (TS 51.011) and USIM (TS 31.102) and ETSI for the further development of the physical card UICC.
There are three operating voltages for SIM cards: 5 V, 3 V and 1.8 V (ISO/IEC 7816-3 classes A, B and C, respectively). The operating voltage of the majority of SIM cards launched before 1998 was 5 V. SIM cards produced subsequently are compatible with 3 V and 5 V. Modern cards support 5 V, 3 V and 1.8 V.
The microcontrollers used for SIM cards come in different configurations. The typical ROM size is between 64 KB and 512 KB, typical RAM size is between 1 KB and 8 KB, and typical EEPROM size is between 16 KB and 512 KB. The ROM contains the operating system of the card and might contain applets where the EEPROM contains the so-called personalization, which consists of security keys, phone book, SMS settings, etc., and operating system patches.
Modern SIM cards allow applications to be loaded when the SIM is in use by the subscriber. These applications communicate with the handset or a server using SIM application toolkit, which was initially specified by 3GPP in TS 11.14 (there is an identical ETSI specification with different numbering). ETSI and 3GPP maintain the SIM specifications; the main specifications are: ETSI TS 102 223, ETSI TS 102 241, ETSI TS 102 588, and ETSI TS 131 111. SIM toolkit applications were initially written in native code using proprietary APIs. In order to allow interoperability of the applications, Java Card was taken as the solution of choice by ETSI. Additional standards and specifications of interest are maintained by Global Platform.
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. (Refer to GSM 11.11)
SIM cards can come in various data capacities, from 32 KB to at least 128 KB. All allow a maximum of 250 contacts to be stored on the SIM, but while the 32 KB has room for 33 Mobile Network Codes (MNCs) or "network identifiers", the 64 KB version has room for 80 MNCs. This is used by network operators to store information on preferred networks, mostly used when the SIM is not in its home market but is roaming. The network operator that issued the SIM card can use this to have a SIM card connect to a preferred network in order to make use of the best price and/or quality network instead of having to pay the network operator that the SIM card 'saw' first. This does not mean that a SIM card can only connect to a maximum of 33 or 80 networks, but this means that the SIM card issuer can only specify up to that number of preferred networks, if a SIM is outside these preferred networks it will use the first or best available network.
Each SIM is internationally identified by its integrated circuit card identifier (ICCID). ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalisation. The ICCID is defined by the ITU-T recommendation E.118 as the Primary Account Number. Its layout is based on ISO/IEC 7812. According to E.118, the number is up to 22 digits long, including a single check digit calculated using the Luhn algorithm. However, the GSM Phase 1 defined the ICCID length as 10 octets (20 digits) with operator-specific structure.
The number is composed of the following subparts:
Issuer identification number (IIN)
Maximum of seven digits:
Individual account identification
With the GSM Phase 1 specification using 10 octets into which ICCID is stored as packed BCD, the data field has room for 20 digits with hexadecimal digit "F" being used as filler when necessary.
In practice, this means that on GSM SIM cards there are 20-digit (19+1) and 19-digit (18+1) ICCIDs in use, depending upon the issuer. However, a single issuer always uses the same size for its ICCIDs.
To confuse matters more, SIM factories seem to have varying ways of delivering electronic copies of SIM personalization datasets. Some datasets are without the ICCID checksum digit, others are with the digit.
As required by E.118, The ITU regularly publishes a list of all internationally assigned IIN codes in its Operational Bulletins. The most recent list, as of June 2012, is in Operational Bulletin No. 1005
SIM cards are identified on their individual operator networks by a unique International Mobile Subscriber Identity (IMSI). Mobile network operators connect mobile phone calls and communicate with their market SIM cards using their IMSIs. The format is:
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 in a database (termed authentication center or AuC) on the carrier's network.
The SIM card is designed not to allow the Ki to 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 cryptographic algorithm for computing SRES_2 (see step 4, below) from the Ki has certain vulnerabilities that can allow the extraction of the Ki from a SIM card and the making of a duplicate SIM card.
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 prior LAI.
Most SIM cards will orthogonally store a number of SMS messages and phone book contacts. The contacts are stored in simple "name and number" pairs: entries containing multiple phone numbers and additional phone numbers will usually not be stored on the SIM card. When a user tries to copy such entries to a SIM the handset's software will break them up into multiple entries, discarding any information that is not a phone number. The number of contacts and messages stored depends on the SIM; early models would store as few as five messages and 20 contacts while modern SIM cards can usually store over 250 contacts.
SIM cards have been made smaller over the years; functionality is independent of format. Full-size SIMs were followed by mini-SIMs, micro-SIMs, and nano-SIMs. SIMs are also made to be embedded in devices.
|SIM card||Introduced||Standard reference||Length (mm)||Width (mm)||Thickness (mm)|
|Full-size (FF)||1991||ISO/IEC 7810:2003, ID-1||85.60||53.98||0.76|
|Mini-SIM (2FF)||late 1990s||ISO/IEC 7810:2003, ID-000||25.00||15.00||0.76|
|Micro-SIM (3FF)||2003||ETSI TS 102 221 V9.0.0, Mini-UICC||15.00||12.00||0.76|
|Nano-SIM (4FF)||early 2012||ETSI TS 102 221 V11.0.0||12.30||8.80||0.67|
|Embedded-SIM||JEDEC Design Guide 4.8, SON-8||6.00||5.00||<1.0|
The first to appear was the full-size or 1FF (1st form factor), the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm).
The mini-SIM card has the same contact arrangement as the full-size SIM card and is normally supplied within a full-size card carrier, attached by a number of linking pieces. This arrangement (defined in ISO/IEC 7810 as ID-1/000) allows such a card to be used in a device requiring a full-size card, or in a device requiring a mini-SIM card after breaking the linking pieces.
The later 3FF card or micro-SIM cards have the same thickness and contact arrangements, but the length and width are further reduced as above.
The micro-SIM was developed by the European Telecommunications Standards Institute (ETSI) along with SCP, 3GPP (UTRAN/GERAN), 3GPP2 (CDMA2000), ARIB, GSM Association (GSMA SCaG and GSMNA), GlobalPlatform, Liberty Alliance, and the Open Mobile Alliance (OMA) for the purpose of fitting into devices otherwise too small for a mini-SIM card.
The micro-SIM was designed for backward compatibility. The major issue for backward compatibility was the contact area of the chip. Retaining the same contact area allows the micro-SIM to be compatible with the prior, larger SIM readers through the use of plastic cutout surrounds. The SIM was also designed to run at the same speed (5 MHz) as the prior version. The same size and positions of pins resulted in numerous "How-to" tutorials and YouTube video with detailed instructions how to cut a mini-SIM card to micro-SIM size with a sharp knife or scissors. These tutorials became very popular among first owners of iPad 3G after its release on April 30, 2010, and iPhone 4 on June 24, 2010.
The chairman of EP SCP, Dr. Klaus Vedder, said
Micro-sim cards were introduced by various mobile service providers for the launch of the original iPad, and later for smartphones, from April 2010. The iPhone 4 was the first smartphone to use a micro-SIM card in June 2010. Later the Samsung Galaxy S3/S4, various Nokia Lumia handsets and the Nokia N9 followed.
On 11 October 2012, mobile service providers began selling the NANOSIM or 4FF (4th form factor) to their mobile users in various countries. The nano sim measures 12.3 × 8.8 × 0.67 mm and reduces the previous format to the contact area while maintaining the existing contact arrangements. A small rim of isolating material is left around the contact area to avoid short circuits with the socket. The 0.7 mm thickness of the NANOSIM is about 15 percent less than its predecessor. 4FF can be put into adapters for use with devices taking 2FF or 3FF SIMs.
SIMs for M2M applications are available in a surface mount SON-8 package which may be soldered directly onto a circuit board.
The surface mount format provides the same electrical interface as the full size, 2FF and 3FF SIM cards, but is soldered to the circuit board as part of the manufacturing process. In M2M applications where there is no requirement to change the SIM card, this avoids the requirement for a connector, improving reliability and security.
In July 2013, it was revealed that Karsten Nohl, a cryptographer and security researcher from SR Labs, had discovered vulnerabilities in some SIM cards that enabled them to be hacked to provide root access. The cards affected use the Data Encryption Standard (DES) which, despite its age, is still used by some operators. Cards using the more recent Advanced Encryption Standard (AES) or Triple DES standards are not affected. Among other risks, the hack could lead to the being remotely cloned or allow payment credentials from the SIM to be stolen. Further details of the research are being given at BlackHat on July 31.
When GSM was already in use, the specifications were further developed and enhanced with functionality like SMS, GPRS, etc. These development steps are referred as releases by ETSI. Within these development cycles, the SIM specification was enhanced as well: new voltage classes, formats and files were introduced. In GSM-only times, the SIM consisted of the hardware and the software. With the advent of UMTS this naming was split: the SIM was now an application and hence only software. The hardware part was called UICC. This split was necessary because UMTS introduced a new application, the Universal Subscriber Identity Module (USIM). The USIM brought, among other things, security improvements like the mutual authentication and longer encryption keys and an improved address book.
"SIM cards" in developed countries are today usually UICCs containing at least a SIM and a USIM application. This configuration is necessary because older GSM only handsets are solely compatible with the SIM [application] and some UMTS security enhancements do rely on the USIM [application].
A virtual SIM is a mobile phone number provided by a mobile network operator that does not require a SIM card to connect phone calls to a user's mobile phone.
The use of SIM cards is mandatory in GSM devices.
The satellite phone networks Iridium, Thuraya and Inmarsat's BGAN also use SIM cards. Sometimes, these SIM cards work in regular GSM phones and also allow GSM customers to roam in satellite networks by using their own SIM card in a satellite phone.
Japan's 2G PDC system (which was shut down in 2012; SoftBank Mobile has already shut down PDC from March 31, 2010) 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.
Japan's current and next generation cellular systems are based on W-CDMA (UMTS) and CDMA2000 and all use SIM cards. However, Japanese CDMA2000-based phones are locked to the R-UIM they are associated with and thus, the cards are not interchangeable with other Japanese CDMA2000 handsets (though they may be inserted into GSM/WCDMA handsets for roaming purposes outside Japan).
CDMA-based devices originally did not use a removable card, and the service for these phones bound to a unique identifier contained in the handset itself. This is most prevalent in operators in the Americas. The first publication of the TIA-820 standard (also known as 3GPP2 C.S0023) in 2000 defined the Removable User Identity Module (R-UIM). Card-based CDMA devices are most prevalent in Asia.
The SIM card introduced a new and significant business opportunity for MVNOs — mobile virtual network operators — who lease capacity from one of the network operators rather than owning or operating a cellular telecoms network, and only provide a SIM card to their customers. MVNOs first appeared in Denmark, Hong Kong, Finland and the UK. Today they exist in over 50 countries, including most of Europe, United States, Canada, Australia and parts of Asia, and account for approximately 10% of all mobile phone subscribers around the world.
On some networks, the mobile phone is locked to its carrier SIM card, meaning that the phone only works with SIM cards from the specific carrier. This is more common in markets where mobile phones are heavily subsidised by the carriers, and the business model depends on the customer staying with the service provider for a minimum term (typically 12 or 24 months). SIM cards that are issued by providers with an associated contract are called Sim only deals. Common examples are the GSM networks in the United States, Canada, Australia, the UK and Poland. Many businesses offer the ability to remove the SIM lock from a phone, effectively making it possible to then use the phone on any network by inserting a different SIM card. Mostly, GSM and 3G mobile handsets can easily be unlocked and used on any suitable network with any SIM card.
In countries where the phones are not subsidised, e.g., India, Israel and Belgium, all phones are unlocked. Where the phone is not locked to its SIM card, the users can easily switch networks by simply replacing the SIM card of one network with that of another while using only one phone. This is typical, for example, among users who may want to optimise their carrier's traffic by different tariffs to different friends on different networks, or when traveling internationally.