This is a convenience library for handling ISO7816-4 application protocol data units (APDUs), a protocol used to communicate with devices like smartcards and, incidentally, the Ledger Nano S and Ledger Blue hardware wallets. APDUs are used for sending commands to the wallet, for example, generating a new public key, or signing a transaction.
The format of a command APDU is:
+-----+-----+----+----+----+-------------+
| CLA | INS | P1 | P2 | Lc | ... data... |
+-----+-----+----+----+----+-------------+
Here, the CLA byte represents the CLASS of the command, the INS byte the INSTRUCTION, P1 and P2 the PARAMETERS to the command, and Lc the LENGTH of the command data.
Generally, Lc may have a variable length, however, the Ledger Bitcoin app assumes it to have one byte, therefore the APDUs are limited to 260 bytes in length (5 header and 255 data bytes).
Run make in the project root. This will create a build directory with the
statically compiled library. Optionally, run make test for the unit tests.
A description of the APDUs implemented by the Ledger Bitcoin app can be found in the technical specification.
Generic information about APDUs in the Ledger SDK is available here.