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 intent
			TECHLISTS = 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 device
				isoDep.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 device
				Log.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 number
					String accountNumber = new String(payload, "UTF-8");
					Log.i(TAG, "Received: " + accountNumber);
					// Inform CardReaderFragment of received account number
					return 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;
	@Override
	public 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());
	}


	@Override
	protected void onPause() {
		super.onPause();

		if (nfcAdapter != null){
			nfcAdapter.disableForegroundDispatch(this);
			disableReaderMode();
		}
	}

	@Override
	protected void onResume() {
		super.onResume();

		if (nfcAdapter != null){
			nfcAdapter.enableForegroundDispatch(this, pendingIntent,
					CardReader.FILTERS, CardReader.TECHLISTS);
			enableReaderMode();
		}
		Log.e("NFC----", IsoDep.class.getName());
		refreshStatus();
	}

	@Override
	protected 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 {

		@Override
		public 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);
		else
			tip = 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);
	}