Introduction to SIM card

The SIM card is a smart chip card with a microprocessor, which is composed of the following modules:

--- CPU

--- Program Memory (ROM)

--- Working memory (RAM)

--- Data Memory (EPROM or E2PROM)

--- Serial communication unit

These five modules must be integrated into an integrated circuit, otherwise their security will be compromised. Because the connection between chips may become an important clue to illegal access and misappropriation of SIM cards.


In actual use, there are two SIM cards with the same function and different forms:

(a) Card type (commonly known as big card) SIM card. This form of SIM card conforms to the ISO...7816 standard for IC cards, similar to IC cards.

(b) An embedded (commonly known as a small card) SIM card, which is only 25 mm x 15 mm in size, is a card that is semi-permanently loaded into a mobile station device.

Both card exteriors are waterproof, wear resistant, antistatic, reliable and highly accurate.


SIM card function
1. Function introduction

The SIM card mainly performs two functions: storing data (controlling access to various data) and completing the whole process of client identity authentication and client information encryption algorithm under security conditions (personal identification number PIN, authentication key Ki is correct).

This function is mainly done by a microprocessor with an operating system in the SIM card. The chip has eight contacts, and the mutual connection with the mobile station device is completed after the power is turned on in the card insertion device. At this point, the operating system and command settings can provide intelligent features for the SIM.

The logical structure of the SIM card intelligence feature is a tree structure. All characteristic parameter information is expressed in the form of data fields, as shown in Figure 7-2. That is, there are three application directories in the root directory, one belongs to the administrative authority application directory, and two belong to the technical management application directory, which are the GSM application directory and the telecommunication application directory respectively. All directories are data fields with binary and formatted data fields. Some of the information in the data field is immutable, that is, it cannot be updated, and some are temporarily stored and need to be updated. Each data field expresses its purpose, the degree of update, the characteristics of the data field (such as the identifier), whether the type is binary or formatted.


In addition to storing normal data fields, the SIM card also stores non-file fields such as an authentication key, a personal identification number, and a personal unlock code.

The SIM card is developed with the GSM phase to develop its phased functionality. Usually the functions proposed in the second phase are based on the first phase, so the SIM card of the second phase is also applicable to the first phase.

SIM card processing

The processing of the SIM card goes through the following steps:

--- Purchase card

--- SIM card processing (write card)

--- data transmission

--- Issue card

During the card manufacturing process, the operating system is loaded into the ROM of the chip. Purchase a card and perform a personalized process on the card before it is delivered to the customer for normal use.

Personalized procedures can be divided into:

(1) Initialization

Generally, the card manufacturer puts the operating system code, such as specific data (factory number, transportation number, etc.), A3, A8 algorithm, etc. into the SIM card, and completes it all at once.

(2) Pre-personalization

Pre-personalize the SIM card, that is, establish a directory structure, format A3, A8, and load the data required by the network operator, such as personal identification code (PIN code), personal identification code key code (PUK code) ), also done in one go.

(3) Personalization

The specified information is loaded into the SIM card, such as IMSI, Ki, Kc, access control level, and the like.

When the data is to be transmitted to the authentication center after the card is written, the IMSI and Ki are encrypted and transmitted by using the advanced algorithm equations dedicated to the data transmission method; if the mailing method is used, the floppy disk containing the data and the SIM card are separately packaged. Mail to prevent loss of confidentiality.

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