private static final int PASS_CODE_LENGTH = 6;static final int INTERVAL = 30;private static final int ADJACENT_INTERVALS = 1;private static final int PIN_MODULO = (int) Math.pow(10, PASS_CODE_LENGTH); // pow是求10的PASS_CODE_LENGTH次方private final Signer signer;private final int codeLength;private final int intervalPeriod;public boolean isCreated;public long timeOffset;private Handler handler;

interface Signer {byte[] sign(byte[] data) throws GeneralSecurityException;}public PasscodeGenerator(Mac mac) {this(mac, PASS_CODE_LENGTH, INTERVAL);}public PasscodeGenerator(final Mac mac, int passCodeLength, int interval) {this(new Signer() {public byte[] sign(byte[] data) {return mac.doFinal(data);}}, passCodeLength, interval);}public PasscodeGenerator(final Mac mac, int passCodeLength, int interval,Handler handler) {this(mac, passCodeLength, interval);this.handler = handler;}public PasscodeGenerator(Signer signer, int passCodeLength, int interval) {this.signer = signer;this.codeLength = passCodeLength;this.intervalPeriod = interval;}

private String padOutput(int value) {String result = Integer.toString(value);for (int i = result.length(); i < codeLength; i++) {result = "0" + result;}return result;}public String generateTimeoutCode(boolean isCreated ,long timeOffset)throws GeneralSecurityException {this.timeOffset = timeOffset;this.isCreated = isCreated;return generateResponseCode(clock.getCurrentInterval());}public String generateResponseCode(long challenge)throws GeneralSecurityException {byte[] value = ByteBuffer.allocate(8).putLong(challenge).array();return generateResponseCode(value);}public String generateResponseCode(byte[] challenge)throws GeneralSecurityException {byte[] hash = signer.sign(challenge);int offset = hash[hash.length - 1] & 0xF;int truncatedHash = hashToInt(hash, offset) & 0x7FFFFFFF;int pinValue = truncatedHash % PIN_MODULO;return padOutput(pinValue);}private int hashToInt(byte[] bytes, int start) {DataInput input = new DataInputStream(new ByteArrayInputStream(bytes,start, bytes.length - start));int val;try {val = input.readInt();} catch (IOException e) {throw new IllegalStateException(e);}return val;}public boolean verifyResponseCode(long challenge, String response)throws GeneralSecurityException {String expectedResponse = generateResponseCode(challenge);return expectedResponse.equals(response);}public boolean verifyTimeoutCode(String timeoutCode)throws GeneralSecurityException {return verifyTimeoutCode(timeoutCode, ADJACENT_INTERVALS,ADJACENT_INTERVALS);}public boolean verifyTimeoutCode(String timeoutCode, int pastIntervals,int futureIntervals) throws GeneralSecurityException {long currentInterval = clock.getCurrentInterval();String expectedResponse = generateResponseCode(currentInterval);if (expectedResponse.equals(timeoutCode)) {return true;}for (int i = 1; i <= pastIntervals; i++) {String pastResponse = generateResponseCode(currentInterval - i);if (pastResponse.equals(timeoutCode)) {return true;}}for (int i = 1; i <= futureIntervals; i++) {String futureResponse = generateResponseCode(currentInterval + i);if (futureResponse.equals(timeoutCode)) {return true;}}return false;}

private IntervalClock clock = new IntervalClock() {public long getCurrentInterval() {long currentTimeSeconds = (System.currentTimeMillis() - timeOffset) / 1000;long count = currentTimeSeconds / getIntervalPeriod();if (isCreated) {long i = getIntervalPeriod()- (currentTimeSeconds % getIntervalPeriod());Message msg = new Message();msg.what = MainActivity.UPDATE_COUNTDOWN;msg.arg1 = (int) i;handler.sendMessage(msg);}return count;}public int getIntervalPeriod() {return intervalPeriod;}};interface IntervalClock {int getIntervalPeriod();long getCurrentInterval();}