APDU reader and writer

Application protocol data units (APDUs) are special communication units that are defined in ISO/IEC 7816-4. The subset of these commands that is used to interact with a Type 4 Tag is implemented in this library.

Command APDUs (C-APDUs) are the commands sent from the polling device, while response APDUs (R-APDUs) are the responses to a specific command received by the polling device from the tag.

The APDU reader/writer module provides functions to encode a C-APDU according to its descriptor and to decode a raw R-APDU data into the appropriate descriptor.

This library can be used with the NFC Reader ST25R3911B library to exchange NFC Type 4 Tag data.

APDU types 

There are three types of APDU that are relevant for a Type 4 Tag platform:

APDU type	Usage
Select	Selecting applications or files.
ReadBinary	Reading data from a file.
UpdateBinary	Writing data to a file.

C-APDU and R-APDU format 

A C-APDU consists of the following fields:

Field	Length	Required	Description
CLA	1 byte	yes	Specifies the security level of the message.
INS	1 byte	yes	Specifies the command type to process.
P1	1 byte	yes	Specifies the first parameter for the chosen command type.
P2	1 byte	yes	Specifies the second parameter for the chosen command type.
Lc	1 or 3 byte	no	Specifies the data length.
Data	Lc bytes	no	Required if LC field is present. Contains payload of C-APDU.
Le	1 or 2 bytes	no	Specifies the expected response body length of R-APDU.