SIM Card Definition

A SIM card (acronym in English for subscriber identity module according to abbreviationfinder) is a removable smart card used in mobile phones and USB modems. SIM cards securely store the subscriber’s service key used to identify themselves to the network, so that it is possible to change the line from one terminal to another simply by changing the card.

The untold story of the SIM Card

The SIM card is today used by millions of mobile phone and data users around the world. But, what do we know about it? How did it come about? What can you do for and for us? Let’s start with some history.

The first SIM card was introduced to the world in the 1980s. What was innovative about the product, in addition to its size, was the possibility of recording the telephone number, without having to memorize it in the mobile phone (previously the number was stored in the phone).

Years later, in the 1990s, GSM technology (Global System for Mobile communications) was presented to the public, whose main characteristic was (and is to this day) today) the possibility of providing voice services over a digital channel. Along with this technology, the SIM card was presented with a standardized format, which was in the form of an electronic ” chip ” and was then known as a Smart Card. It was at that moment when the success of the SIM card began to take shape, since hand in hand with GSM technology, it evolved and became more economical, efficient and comfortable due to its size.

From that moment on, the card acquired new attributes and associated technologies.

If we analyze its characteristics and functionalities, we can compare the SIM card with a “mini” computer, since it has various resources that allow it to act within the mobile device, such as security and identification resources, such as the possibility of providing an identification unique to the user in the mobile network. From this feature derives its name, since the acronym in English means user identification module (Subscriber identification Module). In addition to this, it allows you to use different mobile devices just by changing the SIM card from one phone to another.

Another advantage offered by the SIM card is the possibility of having value-added services such as instant messaging service (Chat), mobile television, games, tones, multimedia services, among others, with very simple interfaces. others. Access to this content is possible thanks to SIM Browsing technology, which consists of a SIM card’s own browser, which also does not require an Internet or WAP be able to function. This also implies that the user does not need to pay for data traffic to be able to purchase services and products from the mobile network, doing so intuitively with just a few clicks. This technology allows a comfortable, efficient and standardized user experience for users, in any type of mobile terminal.

Other services offered by the SIM card are the possibility of accessing social networks and generating agenda backups that can be hosted remotely, thus allowing agility, economy and security: this gives the mobile phone a unique emotional value. It also allows the possibility of hosting useful applications for the user within it without the need to download them to the phone, which in most cases has high costs.

With the aim of acquiring a commitment to social responsibility, the SIM card has now changed its format. Today, the disposable part of the SIM presentation can be transformed into a mini DVD, with interactive, digital, exclusive and even sponsored content, which makes it even more attractive.

In addition to all the attributes that we have detailed, the SIM card also allows access to secure financial services from the mobile phone. It allows the user, for example, to make transfers and check their account, anywhere at any time of the day in a simple and, above all, secure way.

But the innovation does not stop. A new evolution of the SIM card offers the possibility of offering all the services described above, and in addition, it can make the user pay for products or services in ” contactless ” mode, simply by approaching their mobile phone to an access reader. or payment. In this way, the payment is made directly from the user’s account, with the convenience and security that people around the world are looking for today. Examples of this service already exist in public transport payments, with proven success and wide acceptance by the general public.

Due to its versatility in services and applications, the SIM card began to arouse the interest of many consumer companies, becoming a medium in itself. The reason is simple; By adding information about their products and services in the SIM, companies gain visibility, synergy with other media and the possibility of interacting directly with the user without paying high costs in advertising campaigns with little effectiveness and without addressing, carrying out innovative and differentiating actions in their respective markets.

In the sphere of mobile marketing, the SIM card gives the possibility of carrying out interactive messages to create campaigns that reach users directly without intermediaries, generating greater effectiveness and a return on investment that is also greater and more efficient. For example, with just one click, consumers will have access to discounts on purchases, be the first to receive a service, even be summoned to massive events, or depending on where they are, receive last chance prices or the possibility of enter into exclusive activities, allowing greater brand recognition.

In short, when it comes to efficient, complete, interactive and effective media, the SIM card is the answer and the winning media. The SIM card represents the development of technology designed to benefit the public and the market, turning the purchase, access and communication processes into faster, easier and more interactive processes. This confirms that all evolution is for the benefit of all.

SIM Card Usage

The use of the SIM card is mandatory in GSM networks. Its equivalent in UMTS networks is called USIM or UICC (acronym for Universal Integrated Circuit Card, ‘Universal Integrated Circuit Card’), the RUIM (Removable User Identify Module, ‘Removable User Identity Module’) being more popular in CDMA phones.

SIM cards are available in two sizes. The first is similar to that of a credit card (85.60 × 53.98 × 0.76 mm). The second and most popular is the small version (25 × 15 × 0.76 mm).

The specifications applicable to SIM cards are:

  • GSM 11.11: SIM-ME (Mobile Equipment) interface specification.
  • GSM 11.14: SIM Application Toolkit specification for the SIM-ME interface.

Storage capacity

The typical low cost SIM card (GSM 11.11 only) has little memory, 2-3 KB as described by the specification (phone book and little else). This storage space is used directly by the phone. The market segment for low-cost SIM cards is in constant decline.

SIM cards with additional applications (GSM11.14) are available with many different storage capacities, the largest being 512KB. Smaller SIM cards, 32 KB and 16 KB, are the dominant ones in areas with less developed GSM networks. There are also Large Memory SIM cards (‘Large Memory SIM’), with capacities of the order of 128 to 512 kilobytes.

Operating systems

The operating systems for SIM cards are mainly two:

  • Native: vendor-specific, proprietary software(typically corresponding to the low-cost market segment);
  • Java- based: They have the advantage of being hardware independent and interoperable.


SIM cards store network-specific information used to authenticate and identify subscribers on it, the most important being the ICC-ID, IMSI, authentication key (Ki) and local area identification (LAI). The SIM card also stores other carrier-specific data such as SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN) and value service applications. added (VAS). Corresponding descriptions are available in the GSM 11.11 specification.


Each SIM is identified internationally by its ICC-ID (in English) (International Circuit Card ID, ‘International Circuit Card Identifier’). ICC-IDs are stored on SIM cards and are also engraved or printed on the plastic body in a personalization process. In addition, each ICC has a 19-digit personal identification number.


SIM cards are identified in their individual mobile networks by a unique IMSI (International Mobile Subscriber Identify, ‘International Mobile Subscriber Identity’). Mobile phone operators connect calls to mobile phones and communicate with their SIM cards on the market using their IMSI.

Authentication key (Ki)

The Authentication key (Ki) is a 16- byte value used to authenticate SIM cards to the mobile network. Each SIM card has a unique Ki assigned by the operator during the customization process. The Ki is also stored in a specific database called AuC (acronym for Authentication Center) which is implemented as an integral part of the operator ‘s network HLR (acronym for Home Location Register) .


SIM cloning consists of duplicating the GSM SIM.

A SIM card must be inserted in the mobile to connect to the network, except for basic emergency calls, for identification, to make calls or use other paid services.

Authentication process

  1. When the phone is turned on it sends its IMSI to the network operator requesting access and authentication.
  2. The network operator searches its database for the IMSI and the related authentication key (Ki).
  3. The network operator generates a random number (RAND) and signs it with the Ki of the SIM, thus generating a number known as SRES_1 (Signed Response 1, ‘Signed Response 1’).
  4. The network client mobile sends the RAND to the SIM card, which also signs it with its Ki and sends the result (SRES_2) back to the network operator.
  5. The network operator compares its SRES_1 with the SRES_2 generated by the SIM card. If the two numbers match, the SIM is authenticated and network access is granted.

The cryptographic algorithm used in the GSM standard to calculate the SRES_2 has a weak point, allowing the extraction of the Ki from the SIM card and allowing the creation of duplicates (clones).

Local Area Identification

The SIM card stores network status information that is sent from it, such as the Local Area Identification (LAI). Operator networks are divided into local areas, each of which has a unique LAI number. When the mobile terminal changes its location from one local area to another, it stores its new LAI in the SIM card and sends it to the operator to inform the network of its new location. If the terminal is turned off and on again, it will retrieve the SIM card information and search for the LAI it was on. This saves time by avoiding having to search the entire frequency list as it would be done by default.

Local peculiarities


Japan ‘s PDC system also specifies the use of a SIM card, but has never been commercially released. The specification of the interface between the mobile equipment (ME) and the SIM card is given in RCR STD-27 annex 4.


In July 2005, the Finnish government announced that a “Citizen Certificate” (an electronic identity embedded in a SIM card) would be available to anyone residing in Finland before the end of the year, allowing mobile phone users to access electronic services. mobility insurance. The Citizen Certificate has been described as “basically an electronic identity card that will be compatible with various hardware devices, such as mobile phones, PDAs, personal computers, digital television receivers and public web kiosks”.

SIM Card