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。