SIM card - a device that is a subscriber identity module. This is an integrated circuit designed to securely store the International Mobile Subscriber Identification Number (IMSI) and its associated key, which are used to identify and authenticate subscribers on mobile telephony devices (for example, mobile phones and computers). In addition, you can store contact information on many SIM cards.
SIM cards are always used on GSM phones, for CDMA devices they are needed only for new LTE-compatible devices. They can also be used in satellite phones.
The SIM card is part of the universal integrated circuit (UICC) function, which is usually made of PVC with integrated contacts and semiconductors. A SIM card, the device of which is based on digital technology, can transfer data between various mobile devices.
SIM card contains:
- Unique Serial Number (ICCID)
- International Mobile Telecommunications Identifier (IMSI);
- authentication and encryption;
- temporary information about the local network;
- list of services to which the user has access;
- The phone’s SIM card device also has two passwords: a personal identification number (PIN) for normal use and a personal unlock code (PUK) to unlock the PIN code.
History and Market Entry
The SIM format was originally defined by the European Telecommunications Standards Institute in the specification with TS 11.11, which describes the physical and logical properties of the SIM card. With the development of UMTS, specification work was partially carried over to 3GPP.
The first SIM card was developed in 1991 by the Munich smart card manufacturer Giesecke & Devrient, who sold the first 300 copies to the Finnish wireless network operator Radiolinja.
Inactivation
In many “pay-as-you-go” contractual arrangements, you need to periodically use prepayments to avoid expiring your account. This period depends on network operators, but a period of three months is usually determined. This is sometimes due to the fact that the SIM card becomes inactive on the network.
registration
Most countries and operators require identification to activate the service, but there are some exceptions, such as Hong Kong SAR.
What is the sim card of the phone?
Three operating voltages are provided for SIM cards: 5 V, 3 V and 1.8 V. The operating voltage of most SIM cards launched before 1998 was 5 V. The subsequently created cards are compatible with 3 V and 5 V. Modern models support voltage 5 V, 3 V and 1.8 V.
Data
SIM cards store network information used to authenticate and identify subscribers on the network. The most important of these are ICCID, IMSI, Authentication Key (Ki), Local Area Identifier (LAI), and Operator Emergency Number.
The SIM card, the device of which is based on diagrams, also stores other operator-specific data, such as the short message service center number (SMS ServiceServiceName), the name of the service provider (SPN), service number (SDN), Advanceofcharge parameters and applications with value added (VAS).
SIM cards can be delivered in various data volumes from 8 to at least 256 KB. All of them allow you to store a maximum of 250 contacts, but if in the 32 KB version there is space for 33 Mobile Network Codes (MNCs) or “network identifiers”, a 64 KB version holds for 80 MNCs. This indicator is used by network operators to store information about preferred networks and is mainly used when the SIM is not in its home network, but in roaming. What does such a sim card phone mean?
The operator who issued the SIM card can use this to connect the phone to the preferred network in order to use the best commercial agreement for the original network company. This does not mean that the phone containing this SIM can connect to a maximum of 33 or 80 networks, but only that the SIM card issuer can indicate only up to this number of preferred networks. If Simka is outside of these preferred networks, it will use the first or best available of them.
ICCID
Each SIM is internationally identified by an integrated circuit identifier (ICCID). ICCIDs are stored on SIM cards and also engraved or printed on the case during the personalization process.
ICCID is defined by ITU-T Recommendation E.118 as the Primary Number. Its layout is based on ISO / IEC 7812. According to E.118, a number can be up to 22 digits, including one check digit calculated using the Moon algorithm. However, GSM Phase 1 identified the ICCID length as 10 octets (20 digits) with a specific operator structure.
International Mobile Subscriber Identity (IMSI)
SIM cards are identified in the individual networks of operators using the unique international mobile subscriber identity (IMSI). Mobile network operators connect to mobile phone calls and exchange their SIM cards on the market using their IMSI. Their format is as follows.
The first three digits represent the mobile country code (MCC).
The next two or three digits represent the mobile network code (MNC). Three-digit MNC codes are permitted by E.212, but are mainly used in the United States and Canada.
The following numbers are the Mobile Subscriber Identification Number (MSIN). This is usually 10 digits, but the value will be less in the case of a three-digit MNC or if national regulations indicate that the total length of the IMSI should be less than 15 digits. All these numbers differ from country to country, so there may be differences in how the SIM card is arranged. The scheme is standard and factory, the difference is observed only in the recorded information.
Authentication Key (Ki)
Kni is a 128-bit value used to authenticate SIM cards in the GSM mobile network (for the USIM network, you still need Ki, but other parameters are required). Each SIM card stores a unique Ki, assigned to it by the operator during the personalization process. This parameter is also stored in a database (called an authentication center, or AuC) in the network of the service provider.
How is the SIM card based on the foregoing? It is designed in such a way as to prevent Ki from being received using the smart card interface. Instead, the SIM card provides the “Run GSM Algorithm” function, which allows the phone to transfer data to the SIM card, which must be signed with Ki. This in principle makes the use of a SIM card mandatory if Ki cannot be removed from the SIM card or the operator wants to disclose this parameter. In practice, the GSM cryptographic algorithm for computing SRES_2 (see step 4 below) from Ki has certain vulnerabilities that could allow the extraction of this value from the SIM card and the creation of a duplicated SIM card.
Authentication process
When the mobile equipment starts up, it receives the International Mobile Subscriber Identity (IMSI) from the SIM card and transmits it to the mobile operator, requesting access and authentication. Mobile equipment can transfer the PIN code to the SIM card before it opens this information.
Location Area Identification
The SIM stores network status information, which is received from a location area identifier (LAI). Operator networks are divided into areas of location, each of which has a unique LAI number. When the device changes location, it saves the new LAI on the SIM card and sends it back to the carrier network with the new location. If the device operates cyclically, it will extract data from the SIM card and search for the previous LAI. Some listening devices with a SIM card also work on this feature.
SMS messages and contacts
Most SIM cards will by default store some SMS messages and phone book contacts. Contacts are stored in simple “name and number” pairs: records containing several telephone numbers and additional telephone numbers are usually not stored on it. Such conditions are provided by the device of the SIM card. Contacts can be kept very limited. For example, when a user tries to copy such records to a SIM card, the phone software breaks them into several records, discarding any information that is not a phone number.
The number of contacts and messages saved depends on the SIM card. Earlier models will store only five messages and 20 contacts, while modern SIM cards can usually store more than 250 items.
SIM card: device and formats
Over the years, SIM cards have become smaller, and their functionality does not depend on the format. The full-size SIM card was followed by mini-SIM, micro-SIM and nano-SIM. Today, they are even built into devices.
Full-size SIM
A full-sized SIM card (or 1FF, 1st form factor) became the first form factor. It has a credit card size (85.60 × 53.98 × 0.76 mm). Later, smaller "SIM cards" were often sold built-in to a full-sized card, from which they can be pushed.
Mini sim
The mini-SIM card (or 2FF) has the same contact device as the full-size SIM card, and usually comes with a full-size adapter attached to it by connecting elements. This scheme allows you to use it in a device requiring a full-sized card, and in the device requiring a mini-SIM card (after breaking the connecting elements). Since the full-size SIM card is no longer used, some vendors call this form factor a standard or regular SIM card.
Micro sim
A micro-SIM card (or 3FF) has a similar thickness and pin arrangement, but it has a reduced length and width.
The micro-SIM format was introduced by the European Telecommunications Standards Institute (ETSI) for installation on devices too small for a mini-SIM card. The form factor was mentioned in the 3GPP SMG9 UMTS working group, which is the standard setting body for GSM SIM cards, in December 1998, and subsequently agreed at the end of 2003.
Micro SIM has been designed for backward compatibility. The main problem was the contact area of the chip. Keeping the same contact area allows micro-SIM to be compatible with previous, larger SIM-card readers through the use of plastic cutouts. The device was also designed to operate at the same speed (5 MHz) as the previous version. The identical size and position of the contacts led to numerous tutorials and YouTube videos with detailed instructions on how to crop the mini-SIM card to the size of micro-SIM. However, such actions at home sometimes lead to the fact that as a result the SIM card does not correspond to the device or even becomes unusable.
Nano-sim
The nano-SIM (or 4FF) card was introduced on October 11, 2012, when mobile service providers in different countries began to supply it for phones that support this format. Nano-SIM measures 12.3 × 8.8 × 0.67 mm and reduces the previous format to the contact area, while maintaining existing functions. A small rim of insulating material remains around the contact area to avoid short circuits. Nano-SIM has a thickness of 0.67 mm compared to 0.76 mm of its predecessors. 4FF cards can be placed in adapters for use with devices designed for 2FF or 3FF SIM cards and are made thinner for this, but many telephone companies do not recommend this.
The iPhone 5, released in September 2012, was the first device to use activated nano SIM cards, followed by other phones.
The upcoming new generation of SIM cards is called e-SIM or eSIM (embeddedSIM), which is an irreplaceable integrated chip in the SON-8 package - soldering directly on the circuit board. It will have the capabilities of M2M and remote access to the SIM card.