Application Protocol Data Unit (APDU) is a term commonly used in the field of computer networks and communication protocols. It refers to a specific unit or message format utilized in various application-layer protocols and is usually associated with smart card technologies.
An APDU is a standardized data structure that is exchanged between a smart card and a card reader or a host system. It serves as a means of communication between the two entities, allowing them to interact and exchange information. The APDU consists of two main parts, the Command APDU and the Response APDU.
The Command APDU is sent from the host system to the smart card and includes instructions or requests for certain operations to be performed by the card. It typically contains information such as the type of command, parameters, and data necessary for executing the desired operation.
On the other hand, the Response APDU is generated by the smart card in response to the received Command APDU. It includes the result of the operation requested, along with any relevant data or status information.
The structure and format of APDUs may vary depending on the specific application-layer protocol being used. However, they generally adhere to certain standards and guidelines to ensure interoperability and compatibility between different smart card systems.
In summary, the Application Protocol Data Unit (APDU) acts as a communication unit that facilitates the exchange of information and commands between smart cards and host systems or card readers. It provides a standardized format to enable seamless interaction and interoperability within smart card technologies.
