apdu

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';

// SELECT command example
const selectCommand = new Apdu({
  cla: 0x00, // Class byte
  ins: 0xa4, // Instruction: SELECT
  p1: 0x04, // P1: Select by DF name
  p2: 0x00, // P2: First or only occurrence
  data: [0xa0, 0x00, 0x00, 0x00, 0x04, 0x10, 0x10], // AID
  le: 0x00, // Expected response length
});

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
p1	number	Yes	Parameter 1
p2	number	Yes	Parameter 2
data	number[]	No	Command data bytes
le	number	No	Expected response length

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 automatically handles all four APDU cases defined in ISO 7816-4:

• Case 1: No data field, no response data expected (CLA INS P1 P2)
• Case 2: No data field, response data expected (CLA INS P1 P2 Le)
• Case 3: Data field present, no response data expected (CLA INS P1 P2 Lc Data)
• Case 4: Data field present, response data expected (CLA INS P1 P2 Lc Data Le)

License

MIT