MFF (SIM)
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A typical SIM card (mini-SIM with micro-SIM cutout) A
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
mobile phone file:Simkarte NFC SecureElement.jpg, T-Mobile nano-SIM card with NFC capabilities in the SIM tray of an iPhone 6s file:Tf sim both sides.png, A TracFone Wireless SIM card has no distinctive carrier markings and is only marked as a "SIM card" A SIM card (full form Subscriber Identity Module or Subscriber Identification Module) is an
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
(IC) intended to securely store the
international mobile subscriber identity The international mobile subscriber identity (IMSI) is a number that uniquely identifies every user of a cellular network. It is stored as a field and is sent by the mobile device to the network. It is also used for acquiring other details of th ...
(IMSI) number and its related key, which are used to identify and authenticate subscribers on
mobile telephony Mobile telephony is the provision of telephone services to phones which may move around freely rather than stay fixed in one location. Telephony is supposed to specifically point to a voice-only service or connection, though sometimes the li ...
devices (such as
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...
s and
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
s). Technically the actual physical card is known as a
universal integrated circuit card A GSM mobile phone file:SIM-DXAI20210313172217.jpg, alt=Black and white image of the contacts area of a SIM card showing the internal construction, X-Ray of a SIM card showing small rectangular semiconductor chip (central small rectangle) and 5 b ...
(UICC); this
smart card A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authentication device, used to control access to a resource. It is typically a plastic credit card-sized card with an embedded integrated circuit (IC) c ...
is usually made of PVC with embedded contacts and
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
s, with the SIM as its primary component. In practise the term "SIM card" refers to the entire unit and not simply the IC. A SIM contains a unique serial number (ICCID), international mobile subscriber identity (IMSI) number, 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 A personal identification number (PIN), or sometimes redundantly a PIN number or PIN code, is a numeric (sometimes alpha-numeric) passcode used in the process of authenticating a user accessing a system. The PIN has been the key to facilitat ...
(PIN) for ordinary use, and a personal unblocking key (PUK) for PIN unlocking. In Europe, the serial SIM number (SSN) is also sometimes accompanied by an
international article number The International Article Number (also known as European Article Number or EAN) is a standard describing a barcode symbology and numbering system used in global trade to identify a specific retail product type, in a specific packaging configurat ...
(IAN) or a
European article number The International Article Number (also known as European Article Number or EAN) is a standard describing a barcode symbology and numbering system used in global trade to identify a specific retail product type, in a specific packaging configurat ...
(EAN) required when registering online for the subscription of a prepaid card. It is also possible to store contact information on many SIM cards. SIMs are always used on
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
phones; for
CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication ...
phones, they are needed only for LTE-capable handsets. SIM cards can also be used in
satellite phone A satellite telephone, satellite phone or satphone is a type of mobile phone that connects to other phones or the telephone network by radio through orbiting satellites instead of terrestrial cell sites, as cellphones do. The advantage of a sa ...
s, smart watches, computers, or cameras. The first SIM cards were the size of credit and bank cards; sizes were reduced several times over the years, usually keeping electrical contacts the same, so that a larger card could be cut down to a smaller size. SIMs are transferable between different mobile devices by removing the card itself. eSIM is replacing physical SIM cards in some domains, including cellular telephony. eSIM uses a software-based SIM embedded into an unremovable
eUICC eUICC (embedded UICC) refers to the architectural standards published by the GSM Association (GSMA) or implementations of those standard for eSIM, a device used to securely store one or more SIM card profiles, which are the unique identifiers a ...
.


History and procurement

The SIM card is a type of
smart card A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authentication device, used to control access to a resource. It is typically a plastic credit card-sized card with an embedded integrated circuit (IC) c ...
, the basis for which is the
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
(IC) chip. The idea of incorporating a silicon IC chip onto a plastic card originates from the late 1960s. Smart cards have since used
MOS integrated circuit upright=1.6, gate (G), body (B), source (S), and drain (D) terminals. The gate is separated from the body by an gate oxide">insulating layer (pink). The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also ...
chips, along with
MOS memory Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices in which data is stored within metal–oxide–semiconductor (MOS) memory cells on a silic ...
technologies such as
flash memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...
and
EEPROM EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a ...
(electrically
erasable programmable read-only memory An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power su ...
). The SIM was initially specified by the
European Telecommunications Standards Institute The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of Information and communications technology, information and communications. ETSI supports the developmen ...
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 Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...
, 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. The first SIM card was developed in 1991 by Munich smart-card maker
Giesecke & Devrient Giesecke+Devrient, also known as (G+D), is a German company headquartered in Munich that provides banknote and securities printing, smart cards, and cash handling systems. History Founded in 1852 by Hermann Giesecke and Alphonse Devrient, the ...
, who sold the first 300 SIM cards to the Finnish wireless network operator
Radiolinja Radiolinja was a Finnish GSM operator founded on September 19, 1988. On March 27, 1991, the world's first GSM phone call was made on Radiolinja's network. The network was opened for commercial use on July 1, 1991. Radiolinja's slogan was ''So tha ...
. Today, SIM cards are ubiquitous, allowing over 7 billion devices to connect to cellular networks around the world. According to the International Card Manufacturers Association (ICMA), there were 5.4 billion SIM cards manufactured globally in 2016 creating over $6.5 billion in revenue for traditional SIM card vendors. The rise of cellular IoT and 5G networks is predicted to drive the growth of the addressable market for SIM card manufacturers to over 20 billion cellular devices by 2020. The introduction of embedded-SIM (eSIM) and
remote SIM provisioning Remote SIM provisioning is a specification realized by GSMA that allows consumers to remotely activate the subscriber identity module (SIM) embedded in a portable device such as a smart phone, smart watch, fitness band or tablet computer. The spe ...
(RSP) from the GSMA may disrupt the traditional SIM card ecosystem with the entrance of new players specializing in "digital" SIM card provisioning and other value-added services for mobile network operators.


Design

There are three operating voltages for SIM cards: , and (
ISO/IEC 7816 ISO/IEC 7816 is an international standard related to electronic identification cards with contacts, especially smart cards, and more recently, contactless mobile devices, managed jointly by the International Organization for Standardization (ISO) ...
-3 classes A, B and C, respectively). The operating voltage of the majority of SIM cards launched before 1998 was . SIM cards produced subsequently are compatible with and . Modern cards support , and . Modern SIM cards allow applications to load when the SIM is in use by the subscriber. These applications communicate with the handset or a server using
SIM Application Toolkit SIM Application Toolkit (STK) is a standard of the GSM system which enables the subscriber identity module (SIM card) to initiate actions which can be used for various value-added services. Similar standards exist for other network and card systems ...
, 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 (the toolkit for smart cards), ETSI TS 102 241 (
API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standa ...
), ETSI TS 102 588 (application invocation), and ETSI TS 131 111 (toolkit for more SIM-likes). SIM toolkit applications were initially written in native code using proprietary APIs. To provide interoperability of the applications, ETSI chose
Java Card Java Card is a software technology that allows Java-based applications (applets) to be run securely on smart cards and more generally on similar secure small memory footprint deviceswhich are called “secure elements” (SE). Today, a Secure E ...
. A multi-company collaboration called GlobalPlatform defines some extensions on the cards, with additional APIs and features like more cryptographic security and
RFID Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter. When triggered by an electromag ...
contactless use added.


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 A Short Message Service Center (SMSC) is a network element in the mobile telephone network. Its purpose is to store, forward, convert and deliver Short Message Service (SMS) messages. The full designation of an SMSC according to 3GPP is ''Sh ...
) number, service provider name (SPN), service dialling 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 to at least . All can store a maximum of 250 contacts on the SIM, but while the has room for 33
mobile network code The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC). Overview The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
s (MNCs) or ''network identifiers'', the version has room for 80 MNCs. This is used by network operators to store data on preferred networks, mostly used when the SIM is not in its home network but is
roaming Roaming is a wireless telecommunication term typically used with mobile devices, such as mobile phones. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network. Technical ...
. The network operator that issued the SIM card can use this to have a phone connect to a preferred network that is more economic for the provider instead of having to pay the network operator that the phone discovered first. This does not mean that a phone containing this SIM card can connect to a maximum of only 33 or 80 networks, instead it means that the SIM card issuer can specify only up to that number of preferred networks. If a SIM is outside these preferred networks, it uses the first or best available network.


ICCID

Each SIM is internationally identified by its integrated circuit card identifier (ICCID). ICCID is the identifier of the actual SIM card itself: i.e. an identifier for the SIM chip. Nowadays ICCID numbers are also used to identify eSIM profiles, and not only physical SIM cards. 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 ISO/IEC 7812 ''Identification cards – Identification of issuers'' is an international standard published jointly by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). It specifies "a ...
. According to E.118, the number can be up to 19 digits long, including a single check digit calculated using the
Luhn algorithm The Luhn algorithm or Luhn formula, also known as the " modulus 10" or "mod 10" algorithm, named after its creator, IBM scientist Hans Peter Luhn, is a simple checksum formula used to validate a variety of identification numbers, such as credit ca ...
. However, the GSM Phase 1 defined the ICCID length as an opaque data field, 10 octets (20 digits) in length, whose structure is specific to a
mobile network operator A mobile network operator (MNO), also known as a wireless service provider, wireless carrier, cellular company, or mobile network carrier, is a provider of wireless communications services that owns or controls all the elements necessary to sell ...
. The number is composed of the following subparts: Issuer identification number (IIN) Maximum of seven digits: * Major industry identifier (MII), 2 fixed digits, 89 for telecommunication purposes. *
Country code Country codes are short alphabetic or numeric geographical codes (geocodes) developed to represent countries and dependent areas, for use in data processing and communications. Several different systems have been developed to do this. The term '' ...
, 2 or 3 digits, as defined by
ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
recommendation E.164. **
NANP The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling ...
countries, apart from Canada, use 01, i.e. prepending a zero to their common calling code +1 **
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
uses 302 **
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
uses 701, i.e. appending 01 to its calling code +7 **
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...
uses 997, even though it shares the calling code +7 with Russia * Issuer identifier, 1–4 digits. ** Often identical to the
mobile network code The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC). Overview The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
(MNC). Individual account identification * Individual account identification number. Its length is variable, but every number under one IIN has the same length. ** Often identical to the
mobile subscription identification number The mobile identification number (MIN) or mobile subscription identification number (MSIN) refers to the 10- digit unique number that a wireless carrier uses to identify a mobile phone, which is the last part of the international mobile subscriber ...
(MSIN). Check digit * Single digit calculated from the other digits using the
Luhn algorithm The Luhn algorithm or Luhn formula, also known as the " modulus 10" or "mod 10" algorithm, named after its creator, IBM scientist Hans Peter Luhn, is a simple checksum formula used to validate a variety of identification numbers, such as credit ca ...
. With the GSM Phase 1 specification using 10
octets Octet may refer to: Music * Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble ** String octet, a piece of music written for eight string instruments *** Octet (Mendelssohn), 1825 compos ...
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-T updates a list of all current internationally assigned IIN codes in its Operational Bulletins which are published twice a month (the last as of January 2019 was No. 1163 from 1 January 2019). ITU-T also publishes complete lists: as of January 2019, the list issued on 1 December 2018 was current, having all issuer identifier numbers before 1 December 2018.


International mobile subscriber identity (IMSI)

SIM cards are identified on their individual operator networks by a unique
international mobile subscriber identity The international mobile subscriber identity (IMSI) is a number that uniquely identifies every user of a cellular network. It is stored as a field and is sent by the mobile device to the network. It is also used for acquiring other details of th ...
(IMSI).
Mobile network operator A mobile network operator (MNO), also known as a wireless service provider, wireless carrier, cellular company, or mobile network carrier, is a provider of wireless communications services that owns or controls all the elements necessary to sell ...
s connect mobile phone calls and communicate with their market SIM cards using their IMSIs. The format is: * The first three digits represent the
mobile country code The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC). Overview The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
(MCC). * The next two or three digits represent the
mobile network code The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC). Overview The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
(MNC). Three-digit MNC codes are allowed by E.212 but are mainly used in the United States and Canada. One MCC can have both 2 digit and 3 digit MNCs, an example is 350 007. * The next digits represent the mobile subscriber identification number (MSIN). Normally there are 10 digits, but can be fewer in the case of a 3-digit MNC or if national regulations indicate that the total length of the IMSI should be less than 15 digits. * Digits are different from country to country.


Authentication key (Ki)

The Ki is a 128-bit value used in authenticating the SIMs on a
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
mobile network (for USIM network, the K is still needed but other parameters are also needed). Each SIM holds a unique Ki assigned to it by the operator during the personalisation process. The Ki is also stored in a database (termed
authentication center Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobi ...
or AuC) on the carrier's network. The SIM card is designed to prevent someone from getting the Ki by using the smart-card interface. Instead, the SIM card provides a function, ''Run GSM Algorithm'', that the phone uses to pass data to the SIM card to be signed with the Ki. This, by design, makes using 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 a signed response (SRES_1/SRES_2: see steps 3 and 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. Authentication process: # When the mobile equipment starts up, it obtains the international mobile subscriber identity (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 reveals 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, which is a nonce) and signs it with the Ki associated with the IMSI (and stored on the SIM card), computing another number, that is split into the Signed Response 1 (SRES_1, 32 bits) and the encryption key Kc (64 bits). # 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 Signed Response 2 (SRES_2) and Kc, which it gives to the mobile equipment. 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 is granted access to the operator's network. Kc is used to encrypt all further communications between the mobile equipment and the operator.


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 takes data off the SIM, and searches for the prior LAI.


SMS messages and contacts

Most SIM cards store a number of SMS messages and phone book contacts. It stores the contacts in simple "name and number" pairs. Entries that contain multiple phone numbers and additional phone numbers are usually not stored on the SIM card. When a user tries to copy such entries to a SIM, the handset's software breaks them into multiple entries, discarding information that is not a phone number. The number of contacts and messages stored depends on the SIM; early models stored as few as five messages and 20 contacts, while modern SIM cards can usually store over 250 contacts.


Formats

SIM cards have been made smaller over the years; functionality is independent of format. Full-size SIM was followed by mini-SIM, micro-SIM, and nano-SIM. SIM cards are also made to embed in devices. All versions of the non-embedded SIM cards share the same
ISO/IEC 7816 ISO/IEC 7816 is an international standard related to electronic identification cards with contacts, especially smart cards, and more recently, contactless mobile devices, managed jointly by the International Organization for Standardization (ISO) ...
pin arrangement.


Full-size SIM

The ''full-size SIM'' (or 1FF, 1st form factor) was the first form factor to appear. It was the size of a
credit card A credit card is a payment card issued to users (cardholders) to enable the cardholder to pay a merchant for goods and services based on the cardholder's accrued debt (i.e., promise to the card issuer to pay them for the amounts plus the o ...
(85.60 mm × 53.98 mm × 0.76 mm). Later smaller SIMs are often supplied embedded in a full-size card from which they can be removed.


Mini-SIM

The ''mini-SIM'' (or 2FF) 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 ISO/IEC 7810 ''Identification cards — Physical characteristics'' is an international standard that defines the physical characteristics for identification cards. The characteristics specified include: * Physical dimensions * Resistance to b ...
as ID-1/000) lets such a card be used in a device that requires a full-size card or in a device that requires a mini-SIM card, after breaking the linking pieces. As the full-size SIM is no longer used, some suppliers refer to the mini-SIM as a "standard SIM" or "regular SIM".


Micro-SIM

The ''micro-SIM'' (or 3FF) card has the same thickness and contact arrangements, but reduced length and width as shown in the table above. The micro-SIM was introduced by the
European Telecommunications Standards Institute The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of Information and communications technology, information and communications. ETSI supports the developmen ...
(ETSI) along with SCP, 3GPP (UTRAN/GERAN),
3GPP2 The 3rd Generation Partnership Project 2 (3GPP2) is a collaboration between telecommunications associations to make a globally applicable third generation ( 3G) mobile phone system specification within the scope of the ITU's IMT-2000 project. In ...
(CDMA2000),
ARIB The , commonly known as , is a standardization organization in Japan. ARIB is designated as the center of promotion of the efficient use of the radio spectrum and designated frequency change support agency. Its activities include those previously ...
,
GSM Association The GSM Association (commonly referred to as 'the GSMA' or ''Global System for Mobile Communications'', originally ''Groupe Spécial Mobile'') is an industry organisation that represents the interests of mobile network operators worldwide. More ...
(GSMA SCaG and GSMNA), GlobalPlatform,
Liberty Alliance The Liberty Alliance Project was an organization formed in September 2001 to establish standards, guidelines and best practices for identity management in computer systems. It grew to more than 150 organizations, including technology vendors, ...
, and the
Open Mobile Alliance OMA SpecWorks, previously the Open Mobile Alliance (OMA) is a standards organization which develops open, international technical standards for the mobile phone industry. It is a nonprofit Non-governmental organization (NGO), not a formal governme ...
(OMA) for the purpose of fitting into devices too small for a mini-SIM card. The form factor was mentioned in the December 1998 3GPP SMG9
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...
Working Party, which is the standards-setting body for GSM SIM cards, and the form factor was agreed upon in late 2003. 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 makes the micro-SIM 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 videos with detailed instructions how to cut a mini-SIM card to micro-SIM size. 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 The iPhone 4 is a smartphone that was designed and marketed by Apple Inc. It is the fourth generation of the iPhone lineup, succeeding the iPhone 3GS and preceding the 4S. Following a number of notable leaks, the iPhone 4 was first unvei ...
was the first smartphone to use a micro-SIM card in June 2010, followed by many others.


Nano-SIM

The ''nano-SIM'' (or 4FF) card was introduced on 11 October 2012, when mobile service providers in various countries started to supply it for phones that supported the format. The nano-SIM measures 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 nano-SIM is thick, compared to the of its predecessors. 4FF can be put into adapters for use with devices designed for 2FF or 3FF SIMs, and is made thinner for that purpose, and telephone companies give due warning about this. The
iPhone 5 The iPhone 5 is a smartphone that was designed and marketed by Apple Inc. It is the 6th generation iPhone, succeeding both the iPhone 4 and iPhone 4S, and preceding both the iPhone 5S and 5C. It was formally unveiled as part of a press e ...
, released in September 2012, was the first device to use a nano-SIM card, followed by other handsets.


Security

In July 2013, Karsten Nohl, a security researcher from SRLabs, describedRooting SIM cards
SR Labs, accessed 2013-07-22
vulnerabilities in some SIM cards that supported
DES Des is a masculine given name, mostly a short form (hypocorism) of Desmond. People named Des include: People * Des Buckingham, English football manager * Des Corcoran, (1928–2004), Australian politician * Des Dillon (disambiguation), sever ...
, which, despite its age, is still used by some operators. The attack could lead to the phone being remotely
cloned Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means. In nature, some organisms produce clones through asexual reproduction. In the field of biotechnology, c ...
or let someone steal payment credentials from the SIM. Further details of the research were provided at BlackHat on 31 July 2013. In response, the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
said that the development was "hugely significant" and that it would be contacting its members. In February 2015, it was reported by
The Intercept ''The Intercept'' is an American left-wing news website founded by Glenn Greenwald, Jeremy Scahill, Laura Poitras and funded by billionaire eBay co-founder Pierre Omidyar. Its current editor is Betsy Reed. The publication initially reported ...
that the
NSA The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collectio ...
and
GCHQ Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Unit ...
had stolen the encryption keys (Ki's) used by
Gemalto Gemalto was an international digital security company providing software applications, secure personal devices such as smart cards and tokens, and managed services. It was formed in June 2006 by the merger of two companies, Axalto and Gemplus In ...
(the manufacturer of 2 billion SIM cards annually), enabling these intelligence agencies to monitor voice and data communications without the knowledge or approval of cellular network providers or judicial oversight. Having finished its investigation, Gemalto claimed that it has “reasonable grounds” to believe that the NSA and GCHQ carried out an operation to hack its network in 2010 and 2011, but says the number of possibly stolen keys would not have been massive. In September 2019, Cathal Mc Daid, a security researcher from Adaptive Mobile Security, described how vulnerabilities in some SIM cards that contained the S@T Browser library were being actively exploited. This vulnerability was named
Simjacker Simjacker is a cellular software exploit for SIM Cards discovered by AdaptiveMobile Security. 29 countries are vulnerable according to ZDNet. The vulnerability has been exploited primarily in Mexico, but also Colombia and Peru, according to the Wa ...
. Attackers were using the vulnerability to track the location of thousands of mobile phone users in several countries. Further details of the research were provided at VirusBulletin on 3 October 2019.


Developments

When GSM was already in use, the specifications were further developed and enhanced with functionality such as
SMS Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
and
GPRS General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
. 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.


USIM

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 mutual authentication and longer encryption keys and an improved address book.


UICC

"SIM cards" in developed countries today are usually UICCs containing at least a SIM application 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 rely on the USIM application.


Other variants

On
cdmaOne Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995. The ...
networks, the equivalent of the SIM card is the R-UIM and the equivalent of the SIM application is the
CSIM A CDMA subscriber identity module (CSIM) is an application to support CDMA2000 phones that runs on a UICC, with a file structure derived from the R-UIM card. By porting the application to the UICC (Universal Integrated Circuit Card), a card wi ...
. A ''virtual SIM'' is a mobile phone number provided by a
mobile network operator A mobile network operator (MNO), also known as a wireless service provider, wireless carrier, cellular company, or mobile network carrier, is a provider of wireless communications services that owns or controls all the elements necessary to sell ...
that does not require a SIM card to connect phone calls to a user's mobile phone.


Embedded SIM (eSIM)

An embedded SIM (eSIM) is a form of programmable SIM that is embedded directly into a device. The surface mount format provides the same electrical interface as the full size, 2FF and 3FF SIM cards, but is soldered to a 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. An eSIM can be provisioned remotely; end-users can add or remove operators without the need to physically swap a SIM from the device. In September 2017,
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
introduced
Apple Watch Series 3 Apple Watch is a line of smartwatches produced by Apple Inc. It incorporates fitness tracking, health-oriented capabilities, and wireless telecommunication, and integrates with iOS and other Apple products and services. The Apple Watch was rel ...
featuring eSIM.


Integrated SIM (iSIM)

An integrated SIM ( iSIM) is a form of SIM directly integrated into the modem chip or main processor of the device itself. As a consequence they are smaller, cheaper and more reliable than eSIMs, they can improve security and ease the logistics and production of small devices i.e. for
IoT The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other com ...
applications. In 2021, the
German Telekom Deutsche Telekom AG (; short form often just Telekom, DTAG or DT; stylised as ·T·) is a German telecommunications company that is headquartered in Bonn and is the largest telecommunications provider in Europe by revenue. Deutsche Telekom was ...
introduced the nuSIM, an "Integrated SIM for IoT".


Usage in mobile phone standards

The use of SIM cards is mandatory in
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
devices. The
satellite phone A satellite telephone, satellite phone or satphone is a type of mobile phone that connects to other phones or the telephone network by radio through orbiting satellites instead of terrestrial cell sites, as cellphones do. The advantage of a sa ...
networks
Iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...
,
Thuraya Thuraya ( ar, الثريا, Gulf Arabic pron.: ; from the Arabic name for the constellation of the Pleiades, ''Thurayya'') is a United Arab Emirates-based regional mobile-satellite service (MSS) provider. The company operates two geosynchronous ...
and Inmarsat's
BGAN The Broadband Global Area Network (BGAN) is a global satellite network with telephony owned by Inmarsat using portable terminals. The terminals are normally used to connect a laptop computer to broadband Internet in remote locations, although as ...
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 cards in a satellite phone. Japan's 2G PDC system (which was shut down in 2012;
SoftBank Mobile is a Japanese multinational conglomerate holding company headquartered in Minato, Tokyo which focuses on investment management. The Group primarily invests in companies operating in technology, energy, and financial sectors. It also runs the ...
has already shut down PDC from 31 March 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 annexe 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 The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
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 CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible ...
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 Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication ...
-based devices originally did not use a removable card, and the service for these phones is 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 equivalent of a SIM in
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Inte ...
is called the universal integrated circuit card (UICC), which runs a USIM application. The UICC is still colloquially called a ''SIM card''.


SIM and carriers

The SIM card introduced a new and significant business opportunity for 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, the United States, Canada, Mexico, 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, 18 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 travelling internationally. In 2016, carriers started using the concept of automatic SIM reactivation whereby they let users reuse expired SIM cards instead of purchasing new ones when they wish to re-subscribe to that operator. This is particularly useful in countries where prepaid calls dominate and where competition drives high
churn rate Churn rate (sometimes called attrition rate), in its broadest sense, is a measure of the number of individuals or items moving out of a collective group over a specific period. It is one of two primary factors that determine the Steady state, stead ...
s, as users had to return to a carrier shop to purchase a new SIM each time they wanted to churn back to an operator.


SIM-only

Commonly sold as a product by mobile
telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
companies, "SIM-only" refers to a type of
legally binding A contract is a legally enforceable agreement between two or more parties that creates, defines, and governs mutual rights and obligations between them. A contract typically involves the transfer of goods, services, money, or a promise to tran ...
contract between a mobile network provider and a customer. The contract itself takes the form of a credit agreement and is subject to a credit check. Within a SIM-only contract, the mobile network provider supplies their customer with just one piece of hardware, a SIM card, which includes an agreed amount of network usage in exchange for a monthly payment. Network usage within a SIM-only contract can be measured in minutes, text, data or any combination of these. The duration of a SIM-only contract varies depending on the deal selected by the customer, but in the UK they are available over 1, 3, 6, and 12-month periods. SIM-only contracts differ from mobile phone contracts in that they do not include any hardware other than a SIM card. In terms of network usage, SIM-only is typically more cost-effective than other contracts because the provider does not charge more to offset the cost of a mobile device over the contract period. The short contract length is one of the key features of SIM-only made possible by the absence of a mobile device. SIM-only is increasing in popularity very quickly. In 2010 pay monthly based mobile phone subscriptions grew from 41 per cent to 49 per cent of all UK mobile phone subscriptions. According to German research company GfK, 250,000 SIM-only mobile contracts were taken up in the UK during July 2012 alone, the highest figure since GfK began keeping records. Increasing smartphone penetration combined with financial concerns is leading customers to save money by moving onto a SIM-only when their initial contract term is over.


Multiple-SIM devices

Dual SIM Some mobile phones support use of two SIM cards, described as dual SIM operation. When a second SIM card is installed, the phone either allows users to switch between two separate mobile network services manually, has hardware support for keeping ...
devices have two SIM card slots for the use of two SIM cards, from one or multiple carriers. Multiple SIM devices are commonplace in developing markets such as in
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
,
South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;;;;; ...
and
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
, where variable billing rates, network coverage and speed make it desirable for consumers to use multiple SIMs from competing networks. Dual-SIM phones are also useful to separate one's personal phone number from a business phone number, without having to carry multiple devices. Some popular devices, such as the
BlackBerry KeyOne The BlackBerry KeyOne (stylized as BlackBerry KEYone, also known as BlackBerry Key 1, BlackBerry Key1) is a touchscreen-based Android smartphone with an integrated hardware keyboard that is manufactured by TCL Corporation under the brand name o ...
, have dual-SIM variants; however, dual-SIM devices were not common in the US or Europe due to lack of demand. This has changed with mainline products from Apple and Google featuring either two SIM slots or a combination of a physical SIM slot and an eSIM. In September 2018,
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
introduced iPhone XS, iPhone XS Max, and
iPhone XR The iPhone XR (stylized and marketed as iPhone Xʀ; Roman numeral "X" pronounced "ten") is a smartphone designed and manufactured by Apple Inc. It is part of the twelfth generation of the iPhone. Pre-orders began on October 19, 2018, with an ...
featuring Dual SIM (nano-SIM and eSIM) and
Apple Watch Series 4 Apple Watch is a line of smartwatches produced by Apple Inc. It incorporates fitness tracking, health-oriented capabilities, and wireless telecommunication, and integrates with iOS and other Apple products and services. The Apple Watch was rel ...
featuring Dual eSIM.


Thin SIM

A thin SIM (or overlay SIM or SIM overlay) is a very thin device shaped like a SIM card, approximately 120 microns thick. It has contacts on its front and back. It is used by placing it on top of a regular SIM card. It provides its own functionality while passing through the functionality of the SIM card underneath. It can be used to bypass the mobile operating network and run custom applications, particularly on non-programmable cell phones. Its top surface is a connector that connects to the phone in place of the normal SIM. Its bottom surface is a connector that connects to the SIM in place of the phone. With electronics, it can modify signals in either direction, thus presenting a modified SIM to the phone, and/or presenting a modified phone to the SIM. It is a similar concept to the
Game Genie Game Genie is a line of video game cheat cartridges originally designed by Codemasters, sold by Camerica and Galoob. The first device in the series was released in 1990 for the Nintendo Entertainment System, with subsequent devices released for th ...
, which connects between a game console and a game cartridge, creating a modified game. Similar devices have also been developed for iPhones to circumvent SIM card restrictions on carrier-locked models, thus allowing otherwise SIM-locked iPhones to accept SIM cards other than the ones they were authorised to accept. In 2014, Equitel, an MVNO operated by Kenya's Equity Bank, announced its intention to begin issuing thin SIMs to customers, raising security concerns by competition, particularly concerning the safety of mobile money accounts. However, after months of security testing and legal hearings before the country's Parliamentary Committee on Energy, Information and Communications, the
Communications Authority of Kenya The Communications Authority of Kenya (CA) is the regulatory authority for the ICT (Information, Communications and Technology) industry in Kenya with responsibilities in telecommunications, e-commerce, broadcasting and postal/courier services. ...
(CAK) gave the bank the green light to roll out its thin SIM cards.


See also

*
Apple SIM Apple SIM is a proprietary subscriber identity module (SIM) produced by Apple Inc. It is included in GPS + Cellular versions of iPad Air 2 and later, iPad mini 3 and later, and iPad Pro. The Apple SIM supports wireless services across multiple s ...
* eSIM * GSM 03.48 *
International Mobile Equipment Identity The International Mobile Equipment Identity (IMEI) is a numeric identifier, usually unique, for 3GPP and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone but can al ...
(IMEI) *
IP Multimedia Services Identity Module An IP Multimedia Services Identity Module (ISIM) is an application residing on the UICC, an IC card specified in TS 31.101. This module could be on a UMTS 3G or IMS VoLTE network. It contains parameters for identifying and authenticating the us ...
(ISIM) *
Mobile broadband Mobile broadband is the marketing term for Wireless broadband, wireless Internet access via mobile networks. Access to the network can be made through a portable modem, wireless modem, or a Tablet computer, tablet/smartphone (possibly Tetherin ...
*
Mobile equipment identifier A mobile equipment identifier (MEID) is a globally unique number identifying a physical piece of CDMA2000 mobile station equipment. The number format is defined by th3GPP2 report S.R0048but in practical terms, it can be seen as an IMEI but with he ...
(MEID) * Mobile signature *
Regional lockout A regional lockout (or region coding) is a class of digital rights management preventing the use of a certain product or service, such as multimedia or a hardware device, outside a certain region or territory. A regional lockout may be enforced ...
*
SIM cloning Phone cloning is the copying of identity from one cellular device to another. AMPS cloning Analogue mobile telephones were notorious for their lack of security. Casual listeners easily heard conversations as plain narrowband FM; eavesdropper ...
* SIM connector *
Single Wire Protocol The Single Wire Protocol (SWP) is a specification for a single-wire connection between the SIM card and a near field communication (NFC) chip in a cell phone. It was under final review by the European Telecommunications Standards Institute (ETSI). ...
(SWP) *
Tethering Tethering, or phone-as-modem (PAM) is the sharing of a mobile device's Internet connection with other connected computers. Connection of a mobile device with other devices can be done over wireless LAN (Wi-Fi), over Bluetooth or by physical conne ...
*
Transponder In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend word, blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a T ...
* GSM USSD codes Unstructured Supplementary Service Data: list of standard GSM codes for network and SIM related functions *
VMAC VMAC is a block cipher-based message authentication code (MAC) algorithm using a universal hash proposed by Ted Krovetz and Wei Dai in April 2007. The algorithm was designed for high performance backed by a formal analysis. VMAC is designed to h ...
*
W-SIM W-SIM(RX420AL) W-SIM (Willcom-SIM) is a SIM card developed by Willcom which, in addition to standard SIM functions, also has the core components of a cellular telephone ( PHS), such as the radio receiver/transmitter, built inside. It is curr ...
(Willcom-SIM)


References


External links


GSM 11.11
nbsp;– Specification of the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface.

nbsp;– Specification of the SIM Application Toolkit for the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface

nbsp;– Specification of the security mechanisms for SIM application toolkit
GSM 03.48 Java API
nbsp;– API and realization of GSM 03.48 in Java
ITU-T E.118
nbsp;– The International Telecommunication Charge Card 2006 ITU-T {{Use dmy dates, date=December 2020 German inventions Mobile phone standards Cryptographic hardware Smart cards Computer access control