Basic SIM card knowledge

The SIM card (subscriber identity module) is a "smart card" that complies with the GSM specifications. The SIM card has different sizes, the size of a large card is 54mm x 84mm (about the business card size), and that of a small card is 25mm x 15mm (smaller than that of a General stamp ). In fact, what really works on the "big card" is the "small card" on it. The "small card" takes effect only when the small nail covers the size. Currently, the popular style in China is "Small cards". Small cards can also be changed to "big cards" (with a cart ). "Big cards" and "small cards" are applicable to different types of GSM mobile phones. Early models such as Motorola gc87c and 308c use "big cards ", currently, the new models basically use "Small cards ". The SIM card can be inserted into any mobile phone that complies with the GSM specifications. "The phone number with the card is not random", and the call charge is automatically included in the card holder's bill, which is irrelevant to the mobile phone.

Advanced SIM card knowledge

(1) the data stored in the SIM card can be classified into the following four types:

(1) original system data stored by the SIM card manufacturer.
(2) network parameters and user data injected when cards are issued to users by the GSM network operation department or other business departments. Including:
* Authentication and encryption information KI (KCAlgorithmOne of the input parameters: Key number );
* International Mobile user number (imsi );
* A3: imsi authentication algorithm;
* A5: encryption key generation algorithm;
* A8: The User Key (KC) generation algorithm before the key (KC) is generated;
(3) data stored by the user. For example, short messages, fixed dialing, scaling dialing, performance parameters, and phone charge count.
(4) network connection and user information data that are automatically stored and updated during card use. Including the ID (LAI) of the mobile phone's Location Area during the last location registration, the set periodic location update interval, and the temporary mobile phone number (tmsi.

These data are stored in their respective directories. The first type of data is stored in the root directory. When the power supply is enabled, the first type of data enters the root directory, and then enters the related subdirectories according to the command, each directory has an extremely internal data domain protected by its own identification code. data in the data domain can be queried, read, and updated only after verification. The first type of data above is usually permanent and cannot be changed after being injected by the SIM card manufacturer. The second type of data is only accessible and updated by a specialized organization of the network operation department, most of the third and fourth types of data allow users to use any mobile phone for read/write operations.

(2) SIM card structure

(1) The number of phone numbers that SIM cards can store depends on the capacity of the card's EEPROM (2 k, 3 K, 8 K). If there is a storage capacity of 8 KB, the following information can be stored:
* 100 telephone numbers and their corresponding sexual names;
* 15 groups of Short Messages (Short Message );
* Recent numbers allocated to more than 25 groups;
* Four-digit SIM card password (PIN ).
(2) the SIM card is a chip card with a microprocessor. There are five modules in it. Each module has a function: CPU (8 bits ),ProgramMemory Rom (6-16kbit), Working Memory RAM (128-256kbit), data memory EEPROM (2-8kbit) and serial communication unit, these five modules are integrated into an integrated circuit. When the SIM card is connected to the mobile phone, at least five connection lines are required:
* Power supply (VCC)
* Clock (CLK)
* Data I/Q port (data)
* Reset (RST)
* Ground end (Gnd)
(3) The 20-digit ICCD on the back of the SIM card represents the following meanings:
* First 6 digits (898600): the Chinese Code;
* 7th bits: business access number, corresponding to 5, 6, 8, and 9 of 135, 136, 137, 138, 139, and;
* 8th-bit: the SIM card function is generally 0, and the current pre-paid SIM card is I;
* 9th and 10 digits: Code of each province;
* 11 and 12: Year;
* 13: suppliersCode;
* 14-19 digits: user identification code;
* 20 bits: Check bit.

GSM network logon steps

1. after the phone is turned on, it reads imsi (15 digits) and tmsi (4 bytes) from the SIM card.
2. when a mobile phone logs on to the network, imsi or tmsi is sent to the network.
3. if the network determines that the imsi or tmsi is valid, a-bit Rand is generated and sent to the mobile phone.
4. after receiving the Rand, the mobile phone sends the rand to the SIM card.
5. sim performs a3a8 operations on Rand using the ki in it as the key to generate (SRES + Kc);
6. the mobile phone reads (SRES + Kc) (32bit + 64bit) and sends the SRES to the network.
7. the Network performs an a3a8 operation on its own. If the result is the same as the SRES returned by the mobile phone, the user is considered legal.