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/share/link?shareid=3865907609&uk=1765623201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) {
		}
	}

	public static String load(Parcelable parcelable, Resources res) {
		//从Parcelable筛选出各类NFC标准数据
		final Tag tag = (Tag) parcelable;

		final IsoDep isoDep = IsoDep.get(tag);
		Log.e("NFCTAG ID", Util.toHexString(tag.getId(), 0, tag.getId().length));//isodep.transceive("45".getBytes()).toString());
		if (isoDep == null) {
			return 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.e(TAG, "Requesting remote AID: " + SAMPLE_LOYALTY_CARD_AID);
            byte[] command = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID);
            // Send command to remote device
            Log.e(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.e(TAG, "Received: " + accountNumber);
                return accountNumber;
            }
        } catch (IOException e) {
            Log.e(TAG, "Error communicating with card: " + e.toString());
        }

        return null;
	}

    /**
     * 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。