Phone SIM card: device

Sim card is a device that is a subscriber identification module. This is an integrated circuit designed to safely store the International Mobile Subscriber Identity Number (IMSI) and its associated key, which are used to identify and authenticate subscribers on mobile telephony devices (eg, 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 only needed for new LTE-compatible devices. Also they can be used in satellite phones.

The SIM card is part of the Universal Integrated Circuit (UICC) function, which is usually made of PVC with built-in contacts and semiconductors. A sim card, the device of which is based on digital technology, can transfer data between different mobile devices.

The SIM card contains:

• Unique serial number (ICCID);
• International mobile communication identifier (IMSI);
• Authentication and encryption;
• Temporary information about the local network;
• List of services to which the user has access;
• The device of the SIM card of the phone also has two passwords: a personal identification number (PIN) for normal use and a personal unlock code (PUK) for unlocking the PIN code.

History and market entry

Initially, the SIM format was defined by the European Telecommunications Standards Institute in the specification with the number TS 11.11 describing the physical and logical properties of the SIM card. With the development of UMTS, the specification work was partially transferred to 3GPP.

The first SIM card was developed in 1991 by the manufacturer of Munich smart cards Giesecke & Devrient, which sold the first 300 copies to the Finnish operator of the wireless network Radiolinja.

Inactivation

In many "pay-as-you-go" contractual agreements, you must periodically use the prepayment to avoid expiry of your account. This period depends on network operators, but usually a period of three months is defined. This is sometimes due to the fact that the SIM card becomes inactive on the network.

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Most countries and operators require identification to activate the service, but there are some exceptions, such as Hong Kong SAR.

How is the SIM card of the phone?

For SIM-cards, there are three operating voltages: 5 V, 3 V and 1.8 V. The operating voltage of most "simoks", launched before 1998, was 5 V. The subsequently created cards are compatible with 3 V and 5 V. Modern copies support Voltage 5 V, 3 V and 1.8 V.

Data

The SIM cards store information about the network used to authenticate and identify subscribers in the network. The most important of them are ICCID, IMSI, authentication key (Ki), local area identifier (LAI) and operator emergency number.

The SIM card, which is based on schemas, also stores other operator-specific data, such as SMS service center number (SMS ServiceServiceName), service provider name (SPN), service number (SDN) numbers, Advanceofcharge parameters, and applications with Value added (VAS).

SIM cards can be supplied in various volumes of data from 8 to at least 256 KB. All of them allow storing a maximum of 250 contacts, but if there is space for 33 mobile network codes (MNCs) or "network identifiers" in the 32K version, a version on 64 KB 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 device sim card phone?

The operator who released the "sim card" can use this to connect the phone to the preferred network in order to use the best commercial agreement for the source network company. This does not mean that the phone containing this SIM can connect to a maximum of 33 or 80 networks, which means only that the SIM-card issuer can specify only up to this number of preferred networks. If the SIM is outside of these preferred networks, it will use the first or best available ones.

ICCID

Each SIM card is identified at the international level by the integrated circuit identifier (ICCID). ICCIDs are stored on SIM cards, as well as engraved or printed on the case during the personalization process.

The ICCID is determined by ITU-T Recommendation E.118 as the Primary Number. Its layout is based on ISO / IEC 7812. According to E.118, the number can be up to 22 digits, including one check digit calculated using the Moon algorithm. However, GSM Phase 1 defined the ICCID as 10 octets (20 digits) with a specific operator structure.

International Mobile Subscriber Identity (IMSI)

SIM cards are identified in individual operator networks using a 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). The three-digit MNC codes are permitted by E.212, but are mainly used in the United States and Canada.

The following numbers represent the mobile subscriber identification number (MSIN). Usually this is 10 digits, but the value will be smaller in the case of a three-digit MNC or if the national rules indicate that the total IMSI length should be less than 15 digits. All these figures differ from country to country, so there may be differences in how the SIM card is arranged. The circuit is standard and factory, the difference is observed only in the recorded information.

Authentication Key (Ki)

Kni is the 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 the Authentication Center, or AuC) in the carrier's network.

How does the SIM card work in the light of the above? It was designed in such a way that Ki can not be received with the help of a smart card interface. Instead, the SIM card provides the "Launch GSM algorithm" function, which allows the phone to transmit data to the SIM, which must be signed with Ki. This in theory makes the use of a SIM card mandatory, if Ki can not be extracted from the SIM card or the operator wants to open this parameter. In practice, the GSM cryptographic algorithm for calculating SRES_2 (see step 4 below) from Ki has certain vulnerabilities that can allow the extraction of this value from the SIM 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 sends it to the mobile operator, requesting access and authentication. Mobile equipment can transfer the PIN to the SIM card before it opens this information.

Location Area Identification

The SIM stores the network status information that is received from the location-area identifier (LAI). Network operators are divided into areas of location, each of which has a unique LAI number. When the device changes location, it stores the new LAI on the SIM card and sends it back to the operator's network with the new location. If the device operates cyclically, it will retrieve the data from the SIM and search for the previous LAI. This feature is also used by some eavesdropping devices with a SIM card.

SMS messages and contacts

Most SIM-cards will by default store a number of SMS-messages and phone book contacts. Contacts are stored in simple pairs "name and number": records containing several phone numbers and additional phone numbers are usually not stored on it. Such conditions are provided by the SIM card device. Contacts can be kept very limited. For example, when a user attempts to copy such records to a SIM card, the phone's software splits them into several records, discarding any information that is not a phone number.

The number of saved contacts and messages depends on the SIM card. Early 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

With the years of development SIM-cards have become smaller, and their functionality does not depend on the format. The full-sized "sim card" was followed by mini-SIM, micro-SIM and nano-SIM. Today they are even built into devices.

Full-size SIM card

A full-sized SIM card (or 1FF, the 1st form-factor) became the first form-factor. It has the size of a credit card (85.60 × 53.98 × 0.76 mm). Later, smaller "sims" were often sold built-in a full-sized card, from which they can be pushed out.

Mini-SIM

The mini-SIM (or 2FF) card has the same contact device as the full-size SIM card, and is usually supplied in a full-size adapter attached to it by connectors. This scheme allows you to use it in a device that requires a full-size card, and in a device that requires a mini-SIM card (after breaking the connecting elements). Since the full-sized SIM is no longer used, some vendors call this form factor a standard or regular SIM card.

Micro-SIM

The micro-SIM (or 3FF) card has a similar thickness and location of the contacts, but it is distinguished by a reduced length and width.

The micro-SIM format was submitted by the European Telecommunications Standards Institute (ETSI) for installation in devices too small for a mini SIM card. The form factor was mentioned in the working group 3GPP SMG9 UMTS, which is the body setting the standards for GSM SIM cards, in December 1998, and was subsequently agreed at the end of 2003.

The micro-SIM was designed for backward compatibility. The main problem was the contact area of the chip. Saving the same contact area allows the micro SIM to be compatible with previous, larger SIM card readers by using plastic cutouts. The device was also designed to run at the same speed (5 MHz) as the previous version. The same size and position of the contacts resulted in numerous tutorials and YouTube videos with detailed instructions on how to trim a mini-SIM card to the size of a 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 does not at all deteriorate.

Nano-SIM

The nano-SIM (or 4FF) card was introduced on October 11, 2012, when mobile service providers in different countries started shipping it for phones supporting this format. Nano-SIM measures 12.3 × 8.8 × 0.67 mm and reduces the previous format to the contact area, while preserving the existing functions. A small rim of the 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 SIM cards 2FF or 3FF, and for this are made thinner, but many phone companies do not recommend it.

IPhone 5, released in September 2012, was the first device to use activated sim cards nano, followed by other phones.

The upcoming new generation of SIM cards is called e-SIM or eSIM (embeddedSIM), which is an unchangeable embedded 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.