Mastering APDU Commands: A Comprehensive Guide to Adhering to ISO 15693 Standards

To properly build an APDU command based on the ISO 15963 standards, there are a few steps that need to be followed. APDU stands for "Application Protocol Data Unit" and it is a communication protocol used in smart card technology. ISO 15963 is a standard that defines the syntax and structure of APDU commands.

1. Understand the command structure: The first step is to familiarize yourself with the structure of an APDU command. It consists of two parts: the command header and the command body. The command header contains five bytes and specifies the type of command, the length of the command body, and other parameters such as the expected response from the smart card. The command body contains the actual instructions or data that you want to send to the smart card. 2. Determine the command type: There are four types of APDU commands: Case 1, Case 2, Case 3, and Case 4. Each type is used for a specific purpose and has a different structure. It is important to determine the type of command you need to use before building it. Case 1 commands are used for simple requests and responses, while Case 2 commands are used for requests with a short response. Case 3 and Case 4 commands are used for requests with extended responses. 3. Choose the instruction code: The next step is to choose the instruction code, which is a byte that specifies the type of operation you want to perform on the smart card. This can include tasks such as reading data, writing data, or verifying a PIN. The instruction codes are defined in the ISO 7816-4 standard and can vary depending on the type of smart card and its capabilities. 4. Determine the length of the command body: After choosing the instruction code, you need to determine the length of the command body. This is important as it tells the smart card how much data to expect in the command body. The length of the command body is represented by one or two bytes, depending on the type of command. The maximum length of the command body is 255 bytes for Case 1 and Case 2 commands and 65535 bytes for Case 3 and Case 4 commands. 5. Add any necessary parameters: Depending on the type of command and the instruction code chosen, you may need to add additional parameters to the command body. These can include data to be written to the smart card or values to be verified. 6. Calculate the checksum: The last step is to calculate the checksum for the entire APDU command. The checksum is a byte value that is added to the end of the command and is used to verify the integrity of the command. The checksum is calculated by adding all the bytes in the command header and body, then taking the two's complement of the sum. By following these steps, you can properly build an APDU command based on the ISO 15963 standards. It is important to always refer to the appropriate standards and documentation for the specific smart card you are working with to ensure the correct structure and parameters are used.