/* * Copyright (C) 2013 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.example.android.cardemulation; import android.nfc.cardemulation.HostApduService; import android.os.Bundle; import com.example.android.common.logger.Log; import java.util.Arrays; /** * This is a sample APDU Service which demonstrates how to interface with the card emulation support * added in Android 4.4, KitKat. * *

This sample replies to any requests sent with the string "Hello World". In real-world * situations, you would need to modify this code to implement your desired communication * protocol. * *

This sample will be invoked for any terminals selecting AIDs of 0xF11111111, 0xF22222222, or * 0xF33333333. See src/main/res/xml/aid_list.xml for more details. * *

Note: This is a low-level interface. Unlike the NdefMessage many developers * are familiar with for implementing Android Beam in apps, card emulation only provides a * byte-array based communication channel. It is left to developers to implement higher level * protocol support as needed. */ public class CardService extends HostApduService { private static final String TAG = "CardService"; // AID for our loyalty card service. private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222"; // ISO-DEP command HEADER for selecting an AID. // Format: [Class | Instruction | Parameter 1 | Parameter 2] private static final String SELECT_APDU_HEADER = "00A40400"; // "OK" status word sent in response to SELECT AID command (0x9000) private static final byte[] SELECT_OK_SW = HexStringToByteArray("9000"); // "UNKNOWN" status word sent in response to invalid APDU command (0x0000) private static final byte[] UNKNOWN_CMD_SW = HexStringToByteArray("0000"); private static final byte[] SELECT_APDU = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID); /** * Called if the connection to the NFC card is lost, in order to let the application know the * cause for the disconnection (either a lost link, or another AID being selected by the * reader). * * @param reason Either DEACTIVATION_LINK_LOSS or DEACTIVATION_DESELECTED */ @Override public void onDeactivated(int reason) { } /** * This method will be called when a command APDU has been received from a remote device. A * response APDU can be provided directly by returning a byte-array in this method. In general * response APDUs must be sent as quickly as possible, given the fact that the user is likely * holding their device over an NFC reader when this method is called. * *

If there are multiple services that have registered for the same AIDs in * their meta-data entry, you will only get called if the user has explicitly selected your * service, either as a default or just for the next tap. * *

This method is running on the main thread of your application. If you * cannot return a response APDU immediately, return null and use the {@link * #sendResponseApdu(byte[])} method later. * * @param commandApdu The APDU that received from the remote device * @param extras A bundle containing extra data. May be null. * @return a byte-array containing the response APDU, or null if no response APDU can be sent * at this point. */ // BEGIN_INCLUDE(processCommandApdu) @Override public byte[] processCommandApdu(byte[] commandApdu, Bundle extras) { Log.i(TAG, "Received APDU: " + ByteArrayToHexString(commandApdu)); // If the APDU matches the SELECT AID command for this service, // send the loyalty card account number, followed by a SELECT_OK status trailer (0x9000). if (Arrays.equals(SELECT_APDU, commandApdu)) { String account = AccountStorage.GetAccount(this); byte[] accountBytes = account.getBytes(); Log.i(TAG, "Sending account number: " + account); return ConcatArrays(accountBytes, SELECT_OK_SW); } else { return UNKNOWN_CMD_SW; } } // END_INCLUDE(processCommandApdu) /** * Build APDU for SELECT AID command. This command indicates which service a reader is * interested in communicating with. See ISO 7816-4. * * @param aid Application ID (AID) to select * @return APDU for SELECT AID command */ public static byte[] BuildSelectApdu(String aid) { // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X", aid.length() / 2) + aid); } /** * Utility method to convert a byte array to a hexadecimal string. * * @param bytes Bytes to convert * @return String, containing hexadecimal representation. */ public static String ByteArrayToHexString(byte[] bytes) { final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'}; char[] hexChars = new char[bytes.length * 2]; // Each byte has two hex characters (nibbles) int v; for (int j = 0; j < bytes.length; j++) { v = bytes[j] & 0xFF; // Cast bytes[j] to int, treating as unsigned value hexChars[j * 2] = hexArray[v >>> 4]; // Select hex character from upper nibble hexChars[j * 2 + 1] = hexArray[v & 0x0F]; // Select hex character from lower nibble } return new String(hexChars); } /** * Utility method to convert a hexadecimal string to a byte string. * *

Behavior with input strings containing non-hexadecimal characters is undefined. * * @param s String containing hexadecimal characters to convert * @return Byte array generated from input * @throws java.lang.IllegalArgumentException if input length is incorrect */ public static byte[] HexStringToByteArray(String s) throws IllegalArgumentException { int len = s.length(); if (len % 2 == 1) { throw new IllegalArgumentException("Hex string must have even number of characters"); } byte[] data = new byte[len / 2]; // Allocate 1 byte per 2 hex characters for (int i = 0; i < len; i += 2) { // Convert each character into a integer (base-16), then bit-shift into place data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16)); } return data; } /** * Utility method to concatenate two byte arrays. * @param first First array * @param rest Any remaining arrays * @return Concatenated copy of input arrays */ public static byte[] ConcatArrays(byte[] first, byte[]... rest) { int totalLength = first.length; for (byte[] array : rest) { totalLength += array.length; } byte[] result = Arrays.copyOf(first, totalLength); int offset = first.length; for (byte[] array : rest) { System.arraycopy(array, 0, result, offset, array.length); offset += array.length; } return result; } }