ccid

CCID stands for Chip Card Interface Device. It is a USB device class and protocol used by smart card readers to communicate with a host computer. By standardizing how a reader and a card exchange commands and responses, CCID enables software to access smart cards through higher level interfaces such as PC/SC and ISO/IEC 7816 APDUs.

The CCID specification is published by the USB Implementers Forum and is widely adopted by the PC/SC Workgroup. It defines a set of device-to-host and host-to-device messages for transmitting commands and receiving responses (for example, PC_TO_RDR_xxx and RDR_TO_PC_xxx). The standard supports multiple readers, hot-plug operation, and driverless operation on supported operating systems; in practice, Linux uses a generic ccid driver, while Windows and macOS provide native or shipped CCID support.

Typical deployments include payment cards, government identity cards, and security tokens used in banking, e-government, and access control. CCID decouples reader hardware from the card protocol layer, allowing card communication through generic software stacks such as PC/SC or PKCS#11 regardless of the underlying reader vendor. This interoperability simplifies development and deployment of cross-platform smart card solutions.

In summary, CCID provides a standardized USB interface for smart card readers, enabling reliable cross‑platform communication between host systems and smart cards through established card protocols and software frameworks.