Subscriber identity module

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A typical SIM card (mini-SIM)


The SIM circuit is part of the function of a Universal Integrated Circuit Card (UICC) physical smart card, which is usually made of PVC with embedded contacts and semiconductors. "Sim cards" are designed to be transferrable between different mobile devices. The first UICC smart cards were the size of credit and bank cards; the development of physically smaller mobile devices prompted the development of smaller SIM cards where the size of the plastic carrier is reduced while the electrical contacts remain the same.

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.

The first SIM card was made in 1991 by Munich smart-card maker Giesecke & Devrient, who sold the first 300 SIM cards to the Finnish wireless network operator Radiolinja.[1][2]


SIM chip structure and packaging


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[citation needed]. Additional standards and specifications of interest are maintained by Global Platform.



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.[citation needed] This is used by network operators to store information on preferred networks, mostly used when the SIM is not in its home network but is roaming. The network operator that issued the SIM card can use this to have a phone connect to a preferred network, in order to make use of the best commercial agreement for the original network company instead of having to pay the network operator that the phone 'saw' first. This does not mean that a phone containing this SIM card can connect to a maximum of only 33 or 80 networks, but 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 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.[3] 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[4] 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:

  • Issuer identifier, 1–4 digits.

Individual account identification

  • Individual account identification number. Its length is variable, but every number under one IIN will have the same length.

Check 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 November 2013, is in Operational Bulletin No. 1040.

International mobile subscriber identity (IMSI)[edit]


  • The next digits represent the Mobile Subscriber Identification Number (MSIN). Normally there will be 10 digits but would 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)[edit]

The Kni 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[5] that can allow the extraction of the Ki from a SIM card and the making of a duplicate SIM card.

Authentication process:

  1. When the Mobile Equipment starts up, it obtains the 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 will reveal this information.
  3. 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 known as Signed Response 1 (SRES_1).
  4. The operator network then sends the RAND to the Mobile Equipment, which passes it to the SIM card. The SIM card signs it with its Ki, producing SRES_2, which it gives to the Mobile Equipment along with encryption key Kc. The Mobile Equipment passes SRES_2 on to the operator network.
  5. The operator network then compares its computed SRES_1 with the computed SRES_2 that the Mobile Equipment returned. If the two numbers match, the SIM is authenticated and the Mobile Equipment is granted access to the operator's network. Kc is used to encrypt all further communications between the Mobile Equipment and the network.

Location area identity[edit]


SMS messages and contacts[edit]

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.[citation needed]


Full-size SIM (1FF), mini-SIM (2FF), micro-SIM (3FF) and nano-SIM (4FF)
Micro-SIM (from bottom) with mini-SIM and full SIM brackets from Telia in Sweden
The memory film from a micro SIM card without the plastic backing plate, next to a US dime, which is approx. 18 mm in diameter.

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 sizes
Embedded-SIM JEDEC Design Guide 4.8, SON-8 6.00 5.00 <1.0

Full-size SIM[edit]



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 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. Note that some suppliers, such as AT&T, refer to this form factor as a Standard SIM.




The form factor was mentioned in the December 1998 3GPP SMG9 UMTS Working Party, which is the standards-setting body for GSM SIM cards,[9] and the form factor was agreed upon in late 2003.[10]

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.[11]

The chairman of EP SCP, Dr. Klaus Vedder, said[10]

"With this decision, we can see that ETSI has responded to a market need from ETSI customers, but additionally there is a strong desire not to invalidate, overnight, the existing interface, nor reduce the performance of the cards. EP SCP expect to finalise the technical realisation for the third form factor at the next SCP plenary meeting, scheduled for February 2004."

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, the Nokia N9, the Nexus 5 and the Sony Xperia followed.


The nano-SIM (or 4FF) card was introduced on 11 October 2012, when mobile service providers began selling it 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 0.67 mm thickness of the nano-SIM is about 12% less than the 0.76 mm of its predecessor. 4FF can be put into adapters for use with devices taking 2FF or 3FF SIMs; many phone companies however do not recommend using these adapters.[12] The iPhone 5, released in September 2012, was the first device to use a nano-SIM card followed by other handsets including the Nexus 6 and Samsung Galaxy Alpha

Embedded-SIM / Embedded Universal Integrated Circuit Card (eUICC)[edit]

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. GSMA has been discussing the possibilities of a software based SIM card since 2010.[13] While Motorola noted that eUICC is geared at industrial devices, Apple "disagreed that there is any statement forbidding the use of an embedded UICC in a consumer product." in 2012,[14] The European Commission has selected the Embedded UICC format for its in-vehicle emergency call service known as eCall. All new car models in the EU will need to have one by 2015 to instantly connect the car to the emergency services in case of an accident. In Russia there is a similar plan with the ERA GLONASS regional satellite positioning system and in Brazil with the SIMRAV anti-theft system.[15]


In July 2013, it was revealed that Karsten Nohl, a cryptographer and security researcher from SRLabs,[16][17] had discovered vulnerabilities in some SIM cards that enabled them to be hacked to provide root access.[18] The cards affected use the Data Encryption Standard (DES) which, despite its age, is still used by some operators.[18] Cards using the more recent Advanced Encryption Standard (AES) or Triple DES standards are not affected.[18] Among other risks, the hack could lead to the phone being remotely cloned or allow payment credentials from the SIM to be stolen.[18] Further details of the research were to be given at BlackHat on July 31, 2013.[18][19]




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].

The equivalent of SIM on CDMA networks is the R-UIM (and the equivalent of USIM is CSIM).


Usage in mobile phone standards[edit]

The use of SIM cards is mandatory in GSM devices.





The equivalent of a SIM in UMTS is called the Universal Integrated Circuit Card (UICC), which runs a USIM application. The UICC is still colloquially called a SIM card.[citation needed]

SIM and carriers[edit]

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, Mexico, Australia and parts of Asia, and account for approximately 10% of all mobile phone subscribers around the world.



See also[edit]


  2. ^ History of Giesecke & Devrient
  6. ^ "What is a microsim card?". Retrieved 14 October 2012. 
  9. ^ "DRAFT Report of the SMG9 UMTS Working Party, meeting #7 hosted by Nokia in Copenhagen, 15–16 December 1998". 3GPP. 25 January 1999. Retrieved 27 January 2010. One manufacturer stated that it may be difficult to meeting ISO mechanical standards for a combined ID-1/micro-SIM card. 
  10. ^ a b Antipolis, Sophia (8 December 2003). "New form factor for smart cards introduced". SmartCard Trends. Retrieved 30 January 2010. The work item for the so-called Third Form Factor, "3FF", was agreed, after intensive discussions, at the SCP meeting held last week in London. [dead link]
  11. ^ How to make MicroSIM on YouTube
  12. ^ Dr. Klaus Vedder (18 January 2012). "The UICC – Recent Work of ETSI TC Smart Card Platform". ETSI. p. 12. Retrieved 22 July 2012. 
  16. ^ Hacker sollen Kreditkarten freirubbeln, accessed 2013-07-22
  18. ^ a b c d e Rooting SIM cards, SR Labs, accessed 2013-07-22
  19. ^ BlackHat, accessed 2013-07-21

External links[edit]