apdu

Lightweight Node.js library for constructing APDU (Application Protocol Data Unit) commands for smart card communication (ISO 7816-4).

Installation

npm install apdu

Usage

import Apdu from 'apdu';

// Case 1: No data, no response expected (4 bytes)
const case1 = new Apdu({
  cla: 0x00,
  ins: 0xa4,
  p1: 0x04,
  p2: 0x00,
});
console.log(case1.toString()); // "00a40400"

// Case 4: SELECT command with data and response expected
const selectCommand = new Apdu({
  cla: 0x00,
  ins: 0xa4,
  p1: 0x04,
  p2: 0x00,
  data: [0xa0, 0x00, 0x00, 0x00, 0x04, 0x10, 0x10],
  le: 0x00, // Expect response (Le=0x00 means up to 256 bytes)
});
console.log(selectCommand.toString()); // "00a4040007a000000004101000"
console.log(selectCommand.toByteArray()); // Byte array
console.log(selectCommand.toBuffer()); // Node.js Buffer

API

`new Apdu(options)`

Creates a new APDU command.

Option	Type	Required	Description
`cla`	number	Yes	Class byte (0x00-0xFF)
`ins`	number	Yes	Instruction byte (0x00-0xFF)
`p1`	number	Yes	Parameter 1 (0x00-0xFF)
`p2`	number	Yes	Parameter 2 (0x00-0xFF)
`data`	number[]	No	Command data bytes
`le`	number	No	Expected response length (0x00-0xFF). Only included when provided.

Methods

`toString()`

Returns the APDU command as a lowercase hex string.

`toByteArray()`

Returns the APDU command as an array of bytes.

`toBuffer()`

Returns the APDU command as a Node.js Buffer.

APDU Cases

The library correctly handles all four APDU cases defined in ISO 7816-4:

Case 1: No data, no Le → CLA INS P1 P2 (4 bytes)
Case 2: No data, with Le → CLA INS P1 P2 Le (5 bytes)
Case 3: With data, no Le → CLA INS P1 P2 Lc Data
Case 4: With data, with Le → CLA INS P1 P2 Lc Data Le

Note: Le is only included in the output when explicitly provided. This ensures correct Case 1/3 handling where no response is expected.

License

MIT

tomkp/apdu