The reason why smart cards can support such complex applications is the convenience and security of the Chip Operating System (hereinafter referred to as COS).

Compared with the traditional PC software system, COS is similar to the operating system of Windows and UNIX in the IC card system, so it is usually called the card operating system. Functionally speaking, COS is not a complete operating system, more similar to a monitoring program, and its main functions include the following parts.
* IC card power-on reset

COS runs directly on the chip platform and is the operating platform for all application code. The starting point of the COS program operation is the power-on reset of the card. After the IC card is inserted into the card reader and powered up, the chip automatically starts running the program from the specified position. At this time, the COS needs to set all the environments and wait for the execution of the application.

* Chip bottom hardware driver

Since the COS runs directly on the chip platform, the operations of the various components of the chip are completed in the COS, including memory read and write, use of the computing coprocessor, port monitoring, and use of a random number generator.

* Card external interface interaction

The chip sends and receives data through the I/O port. The data format must be in accordance with the corresponding international specifications. According to the interface provided by the chip, both contact and non-contact have different processing flows.

* Maintenance of memory space inside the card

The memory space of the card is the data temporary space of the program and is one of the important resources in the IC card. Due to factors such as price, the memory space is usually very limited. COS needs to provide a corresponding guarantee mechanism to allocate memory reasonably, and to distinguish the protection of the system and the application's respective memory space to ensure security.

* Maintenance of in-card file system

The data exists in the form of files in the card. Similar to the file system of the operating system in the PC, the file system of COS must provide basic operations such as file creation, modification, deletion, and maintenance. In addition, file addressing and file access are provided. Security controls and more.

* System operation security control

For COS-level system security, it is mainly manifested in two aspects, one is the security guarantee capability of COS for data in the card, and the other is the security definition provided by COS. Applications should be able to customize the access control of their data within the card using the security definitions provided by COS. Security control is the core of COS and the most important part of measuring a COS performance.

* Processing of commands

The interface between the card and the application is in the form of command and response. The COS uses the I/O interface to accept the command message, and processes the message according to the content of the message and the corresponding logical COS, and finally returns the response through the I/O interface. . The processing of the command is the basis for the final test of the correctness of the COS.

* Application code execution

The COS processes the application commands and will eventually call the application code. COS needs to implement the calling mechanism that defines the application code and the COS system, that is, to be able to complete the application logic completely, and to strictly control the running space of the application code and COS code.

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