移动支付之Android HCE的基本使用

本文来自http://blog.csdn.net/hellogv/ ，引用必须注明出处！

最近NFC支付挺火的，趁国庆宅在家，学习下Android 卡模拟(Host-based Card Emulation)。HCE的特点是模拟智能IC卡(ISO 7816-4)，可用于金融和行业应用，相应地，CardReader例子中使用IsoDep。

智能IC卡本身是一个微型计算机，常见为Java Card平台，特别是多功能集于一身的卡（如联名卡），Java Card比J2ME更加硬件受限。Java Card可以运行一到多个Java Applet，这些Applet也就是卡应用，例如一张能刷公交的银行卡可能就包含了2个Applet。每个Applet都有一个AID，受理终端（刷卡设备）通过AID来找到对应的卡应用（受理终端向卡发送SELECT命令），受理终端找到对应的卡应用后就可以进行数据交互，交互的数据一般是密文，不联机解密的话，用对称算法，联机解密的话，用非对称和对称算法都行。

HCE是软件模拟的智能IC卡，所以也会有AID。本文CardEmulation只注册一个AID。本文的代码改自Android 4.4 Sample，没改动CardEmulation，简化CardReader并支持Android 2.3系统，适应低版本的NFC手机做虚拟卡的卡读取了。使用努比亚Z7 MAX做CardEmulation，小米 2A作CardReader。本文的代码可以到http://pan.baidu.com/s/1o6JnXr0下载。个人觉得阅读CardReader核心代码更能了解2者交互的过程：

public final class CardReader {    private static final String TAG = "LoyaltyCardReader";    // 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 = {(byte) 0x90, (byte) 0x00};public static String[][] TECHLISTS;public static IntentFilter[] FILTERS;static {try {//the tech lists used to perform matching for dispatching of the ACTION_TECH_DISCOVERED intentTECHLISTS = new String[][] { { IsoDep.class.getName() },{ NfcV.class.getName() }, { NfcF.class.getName() }, };FILTERS = new IntentFilter[] { new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED, "*/*") };} catch (Exception e) {}}    static public String tagDiscovered(Tag tag) {Log.i(TAG, "New tag discovered");// Android's Host-based Card Emulation (HCE) feature implements the// ISO-DEP (ISO 14443-4)// protocol.//// In order to communicate with a device using HCE, the discovered tag// should be processed// using the IsoDep class.IsoDep isoDep = IsoDep.get(tag);if (isoDep != null) {try {// Connect to the remote NFC deviceisoDep.connect();// Build SELECT AID command for our loyalty card service.// This command tells the remote device which service we wish to// communicate with.Log.i(TAG, "Requesting remote AID: " + SAMPLE_LOYALTY_CARD_AID);byte[] command = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID);// Send command to remote deviceLog.i(TAG, "Sending: " + ByteArrayToHexString(command));byte[] result = isoDep.transceive(command);// If AID is successfully selected, 0x9000 is returned as the// status word (last 2// bytes of the result) by convention. Everything before the// status word is// optional payload, which is used here to hold the account// number.int resultLength = result.length;byte[] statusWord = { result[resultLength - 2],result[resultLength - 1] };byte[] payload = Arrays.copyOf(result, resultLength - 2);if (Arrays.equals(SELECT_OK_SW, statusWord)) {// The remote NFC device will immediately respond with its// stored account numberString accountNumber = new String(payload, "UTF-8");Log.i(TAG, "Received: " + accountNumber);// Inform CardReaderFragment of received account numberreturn accountNumber;}} catch (IOException e) {Log.e(TAG, "Error communicating with card: " + e.toString());}}return null;}public static String load(Parcelable parcelable) {// 从Parcelable筛选出各类NFC标准数据final Tag tag = (Tag) parcelable;return tagDiscovered(tag);}    /**     * 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 class 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];        int v;        for ( int j = 0; j < bytes.length; j++ ) {            v = bytes[j] & 0xFF;            hexChars[j * 2] = hexArray[v >>> 4];            hexChars[j * 2 + 1] = hexArray[v & 0x0F];        }        return new String(hexChars);    }    /**     * Utility class to convert a hexadecimal string to a byte string.     *     * <p>Behavior with input strings containing non-hexadecimal characters is undefined.     *     * @param s String containing hexadecimal characters to convert     * @return Byte array generated from input     */    public static byte[] HexStringToByteArray(String s) {        int len = s.length();        byte[] data = new byte[len / 2];        for (int i = 0; i < len; i += 2) {            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)                    + Character.digit(s.charAt(i+1), 16));        }        return data;    }

简单地说：

1。CardReader使用SAMPLE_LOYALTY_CARD_AID + SELECT_APDU_HEADER 生成 SELECT APDU;

2。CardReader发送SELECT APDU到CardEmulation后，CardEmulation返回SELECT_OK_SW + accountNumber。

其中SAMPLE_LOYALTY_CARD_AID ，SELECT_APDU_HEADER ，SELECT_OK_SW 都必须是CardReader与CardEmulation双方定义好的。

另外，CardReader在4.4和4.4以下系统的用法也略有不同，4.4以下系统用onNewIntent（），4.4系统就要通过enableReaderMode（）方法，如果4.4系统用onNewIntent（）的话，会导致一直P2P，而不是卡与读卡器的关系。

public final class NFCard extends Activity {private NfcAdapter nfcAdapter;private PendingIntent pendingIntent;private EditText board;private int sysVersion;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.cardreader);board = (EditText) this.findViewById(R.id.editText1);nfcAdapter = NfcAdapter.getDefaultAdapter(this);pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this,getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);//区分系统版本sysVersion = Integer.parseInt(VERSION.SDK);if(sysVersion<19)onNewIntent(getIntent());}@Overrideprotected void onPause() {super.onPause();if (nfcAdapter != null){nfcAdapter.disableForegroundDispatch(this);disableReaderMode();}}@Overrideprotected void onResume() {super.onResume();if (nfcAdapter != null){nfcAdapter.enableForegroundDispatch(this, pendingIntent,CardReader.FILTERS, CardReader.TECHLISTS);enableReaderMode();}Log.e("NFC----", IsoDep.class.getName());refreshStatus();}@Overrideprotected void onNewIntent(Intent intent) {super.onNewIntent(intent);final Parcelable p = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);Log.d("NFCTAG", intent.getAction());board.setText((p != null) ? CardReader.load(p) : null);}    @TargetApi(19)     private void enableReaderMode() {    if(sysVersion<19)    return;            int READER_FLAGS = NfcAdapter.FLAG_READER_NFC_A | NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK;        if (nfcAdapter != null) {        nfcAdapter.enableReaderMode(this, new MyReaderCallback(), READER_FLAGS, null);        }    }    @TargetApi(19)     private void disableReaderMode() {    if(sysVersion<19)    return;            if (nfcAdapter != null) {        nfcAdapter.disableReaderMode(this);        }    }    @TargetApi(19) public class MyReaderCallback implements NfcAdapter.ReaderCallback {@Overridepublic void onTagDiscovered(final Tag arg0) {NFCard.this.runOnUiThread(new Runnable() {            @Override            public void run() {                        board.setText(CardReader.tagDiscovered(arg0));            }        });}}    protected void onActivityResult(int requestCode, int resultCode, Intent data) {refreshStatus();}private void refreshStatus() {final String tip;if (nfcAdapter == null)tip = this.getResources().getString(R.string.tip_nfc_notfound);else if (nfcAdapter.isEnabled())tip = this.getResources().getString(R.string.tip_nfc_enabled);elsetip = this.getResources().getString(R.string.tip_nfc_disabled);final StringBuilder s = new StringBuilder(this.getResources().getString(R.string.app_name));s.append("  --  ").append(tip);setTitle(s);}