Write Data
This command allows writing data to either a protected user memory slot (with access control) or a public custom byte area (included in SELECT response). Writing to protected slots requires authentication via PIN or challenge-response and must occur over a Secure Channel.
def write_data(P1: Int, data: bytes, P2: Int):
card.write_data(P1, data, P2)
For example, write_data(0, b"Antoine DATA Card" * 12, 0)
Application Protocol Data Unit (APDU) Components
The following table outlines the components of the Application Protocol Data Unit (APDU).
Field | Description | Value |
CLA | This field specifies the class of the instruction. | 0x80 |
INS | This field specifies the particular command or operation that the smart card or secure element should execute. | 0xFC |
P1 | First parameter of the instruction that specifies the details about the operation being requested. | 0x00 or 0x01 |
P2 | First parameter of the instruction that specifies additional details about the operation being requested. | 0x00 (or page index) |
Data | Key data | Data to be written (to the user protected slot, or select custom bytes) |
📘 Note
- This command writes data either to secure user memory (P1 = 0x00) in paginated format, or to public custom bytes (P1 = 0x01).
- Secure Channel and authentication (via PIN or challenge-response) must be established.
- Protected user memory pages must be written in order, starting from page 0.
- Writing to public custom bytes is not protected and is visible to anyone.
📘 Prerequisites
The secure channel must be open and authentication must be successfully performed via PIN verification or challenge-response.
- For writing user-protected memory (P1 = 0x00):
- Previous pages must be fully written in order (e.g., page 0 before page 1).
- The data length must be less than or equal to 1200 bytes.
- For writing public custom bytes (P1 = 0x01):
- The data length must be exactly 16 bytes.
Response
The following table outlines the possible responses that you will receive:
Response Code | Description |
0x9000 | Success |
0x6985 | The PIN is not validated or user challenge-response not performed or previous data pages not fully written |
0x6700 | Data length incorrect (> 1200 bytes P1=0, or !=16 when P1=1) |
0x6A86 | P1 not 0 nor 1, or P2 out of range |
0x6982 | outside the secure channel if data is too large |