1 /* 2 * Copyright (C) 2013 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.example.android.cardemulation; 18 19 import android.nfc.cardemulation.HostApduService; 20 import android.os.Bundle; 21 import com.example.android.common.logger.Log; 22 23 import java.util.Arrays; 24 25 /** 26 * This is a sample APDU Service which demonstrates how to interface with the card emulation support 27 * added in Android 4.4, KitKat. 28 * 29 * <p>This sample replies to any requests sent with the string "Hello World". In real-world 30 * situations, you would need to modify this code to implement your desired communication 31 * protocol. 32 * 33 * <p>This sample will be invoked for any terminals selecting AIDs of 0xF11111111, 0xF22222222, or 34 * 0xF33333333. See src/main/res/xml/aid_list.xml for more details. 35 * 36 * <p class="note">Note: This is a low-level interface. Unlike the NdefMessage many developers 37 * are familiar with for implementing Android Beam in apps, card emulation only provides a 38 * byte-array based communication channel. It is left to developers to implement higher level 39 * protocol support as needed. 40 */ 41 public class CardService extends HostApduService { 42 private static final String TAG = "CardService"; 43 // AID for our loyalty card service. 44 private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222"; 45 // ISO-DEP command HEADER for selecting an AID. 46 // Format: [Class | Instruction | Parameter 1 | Parameter 2] 47 private static final String SELECT_APDU_HEADER = "00A40400"; 48 // "OK" status word sent in response to SELECT AID command (0x9000) 49 private static final byte[] SELECT_OK_SW = HexStringToByteArray("9000"); 50 // "UNKNOWN" status word sent in response to invalid APDU command (0x0000) 51 private static final byte[] UNKNOWN_CMD_SW = HexStringToByteArray("0000"); 52 private static final byte[] SELECT_APDU = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID); 53 54 /** 55 * Called if the connection to the NFC card is lost, in order to let the application know the 56 * cause for the disconnection (either a lost link, or another AID being selected by the 57 * reader). 58 * 59 * @param reason Either DEACTIVATION_LINK_LOSS or DEACTIVATION_DESELECTED 60 */ 61 @Override onDeactivated(int reason)62 public void onDeactivated(int reason) { } 63 64 /** 65 * This method will be called when a command APDU has been received from a remote device. A 66 * response APDU can be provided directly by returning a byte-array in this method. In general 67 * response APDUs must be sent as quickly as possible, given the fact that the user is likely 68 * holding their device over an NFC reader when this method is called. 69 * 70 * <p class="note">If there are multiple services that have registered for the same AIDs in 71 * their meta-data entry, you will only get called if the user has explicitly selected your 72 * service, either as a default or just for the next tap. 73 * 74 * <p class="note">This method is running on the main thread of your application. If you 75 * cannot return a response APDU immediately, return null and use the {@link 76 * #sendResponseApdu(byte[])} method later. 77 * 78 * @param commandApdu The APDU that received from the remote device 79 * @param extras A bundle containing extra data. May be null. 80 * @return a byte-array containing the response APDU, or null if no response APDU can be sent 81 * at this point. 82 */ 83 // BEGIN_INCLUDE(processCommandApdu) 84 @Override processCommandApdu(byte[] commandApdu, Bundle extras)85 public byte[] processCommandApdu(byte[] commandApdu, Bundle extras) { 86 Log.i(TAG, "Received APDU: " + ByteArrayToHexString(commandApdu)); 87 // If the APDU matches the SELECT AID command for this service, 88 // send the loyalty card account number, followed by a SELECT_OK status trailer (0x9000). 89 if (Arrays.equals(SELECT_APDU, commandApdu)) { 90 String account = AccountStorage.GetAccount(this); 91 byte[] accountBytes = account.getBytes(); 92 Log.i(TAG, "Sending account number: " + account); 93 return ConcatArrays(accountBytes, SELECT_OK_SW); 94 } else { 95 return UNKNOWN_CMD_SW; 96 } 97 } 98 // END_INCLUDE(processCommandApdu) 99 100 /** 101 * Build APDU for SELECT AID command. This command indicates which service a reader is 102 * interested in communicating with. See ISO 7816-4. 103 * 104 * @param aid Application ID (AID) to select 105 * @return APDU for SELECT AID command 106 */ BuildSelectApdu(String aid)107 public static byte[] BuildSelectApdu(String aid) { 108 // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] 109 return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X", 110 aid.length() / 2) + aid); 111 } 112 113 /** 114 * Utility method to convert a byte array to a hexadecimal string. 115 * 116 * @param bytes Bytes to convert 117 * @return String, containing hexadecimal representation. 118 */ ByteArrayToHexString(byte[] bytes)119 public static String ByteArrayToHexString(byte[] bytes) { 120 final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'}; 121 char[] hexChars = new char[bytes.length * 2]; // Each byte has two hex characters (nibbles) 122 int v; 123 for (int j = 0; j < bytes.length; j++) { 124 v = bytes[j] & 0xFF; // Cast bytes[j] to int, treating as unsigned value 125 hexChars[j * 2] = hexArray[v >>> 4]; // Select hex character from upper nibble 126 hexChars[j * 2 + 1] = hexArray[v & 0x0F]; // Select hex character from lower nibble 127 } 128 return new String(hexChars); 129 } 130 131 /** 132 * Utility method to convert a hexadecimal string to a byte string. 133 * 134 * <p>Behavior with input strings containing non-hexadecimal characters is undefined. 135 * 136 * @param s String containing hexadecimal characters to convert 137 * @return Byte array generated from input 138 * @throws java.lang.IllegalArgumentException if input length is incorrect 139 */ HexStringToByteArray(String s)140 public static byte[] HexStringToByteArray(String s) throws IllegalArgumentException { 141 int len = s.length(); 142 if (len % 2 == 1) { 143 throw new IllegalArgumentException("Hex string must have even number of characters"); 144 } 145 byte[] data = new byte[len / 2]; // Allocate 1 byte per 2 hex characters 146 for (int i = 0; i < len; i += 2) { 147 // Convert each character into a integer (base-16), then bit-shift into place 148 data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) 149 + Character.digit(s.charAt(i+1), 16)); 150 } 151 return data; 152 } 153 154 /** 155 * Utility method to concatenate two byte arrays. 156 * @param first First array 157 * @param rest Any remaining arrays 158 * @return Concatenated copy of input arrays 159 */ ConcatArrays(byte[] first, byte[]... rest)160 public static byte[] ConcatArrays(byte[] first, byte[]... rest) { 161 int totalLength = first.length; 162 for (byte[] array : rest) { 163 totalLength += array.length; 164 } 165 byte[] result = Arrays.copyOf(first, totalLength); 166 int offset = first.length; 167 for (byte[] array : rest) { 168 System.arraycopy(array, 0, result, offset, array.length); 169 offset += array.length; 170 } 171 return result; 172 } 173 } 174