HOTP(K,C) = Truncate(HMAC-SHA-1(K,C)) 

package com.auth.google; 
 
import java.security.InvalidKeyException; 
import java.security.NoSuchAlgorithmException; 
import java.security.SecureRandom; 
import javax.crypto.Mac; 
import javax.crypto.spec.SecretKeySpec; 
import org.apache.commons.codec.binary.Base32; 
import org.apache.commons.codec.binary.Base64; 
 
/** 
 * 
 * 
 * google身份驗證器，java服務端實現 
 * 
 * @author yangbo 
 * 
 * @version 創建時間：2017年8月14日 上午10:10:02 
 * 
 * 
 */ 
public class GoogleAuthenticator { 
 
 // 生成的key長度( Generate secret key length) 
 public static final int SECRET_SIZE = 10; 
 
 public static final String SEED = "g8GjEvTbW5oVSV7avL47357438reyhreyuryetredLDVKs2m0QN7vxRs2im5MDaNCWGmcD2rvcZx"; 
 // Java實現隨機數算法 
 public static final String RANDOM_NUMBER_ALGORITHM = "SHA1PRNG"; 
 // 最多可偏移的時間 
 int window_size = 3; // default 3 - max 17 
 
 /** 
 * set the windows size. This is an integer value representing the number of 
 * 30 second windows we allow The bigger the window, the more tolerant of 
 * clock skew we are. 
 * 
 * @param s 
 *  window size - must be >=1 and <=17. Other values are ignored 
 */ 
 public void setWindowSize(int s) { 
 if (s >= 1 && s <= 17) 
  window_size = s; 
 } 
 
 /** 
 * Generate a random secret key. This must be saved by the server and 
 * associated with the users account to verify the code displayed by Google 
 * Authenticator. The user must register this secret on their device. 
 * 生成一個隨機秘鑰 
 * 
 * @return secret key 
 */ 
 public static String generateSecretKey() { 
 SecureRandom sr = null; 
 try { 
  sr = SecureRandom.getInstance(RANDOM_NUMBER_ALGORITHM); 
  sr.setSeed(Base64.decodeBase64(SEED)); 
  byte[] buffer = sr.generateSeed(SECRET_SIZE); 
  Base32 codec = new Base32(); 
  byte[] bEncodedKey = codec.encode(buffer); 
  String encodedKey = new String(bEncodedKey); 
  return encodedKey; 
 } catch (NoSuchAlgorithmException e) { 
  // should never occur... configuration error 
 } 
 return null; 
 } 
 
 /** 
 * Return a URL that generates and displays a QR barcode. The user scans 
 * this bar code with the Google Authenticator application on their 
 * smartphone to register the auth code. They can also manually enter the 
 * secret if desired 
 * 
 * @param user 
 *  user id (e.g. fflinstone) 
 * @param host 
 *  host or system that the code is for (e.g. myapp.com) 
 * @param secret 
 *  the secret that was previously generated for this user 
 * @return the URL for the QR code to scan 
 */ 
 public static String getQRBarcodeURL(String user, String host, String secret) { 
 String format = "http://www.google.com/chart&#63;chs=200x200&chld=M%%7C0&cht=qr&chl=otpauth://totp/%s@%s&#63;secret=%s"; 
 return String.format(format, user, host, secret); 
 } 
 
 /** 
 * 生成一個google身份驗證器，識別的字符串，只需要把該方法返回值生成二維碼掃描就可以了。 
 * 
 * @param user 
 *  賬號 
 * @param secret 
 *  密鑰 
 * @return 
 */ 
 public static String getQRBarcode(String user, String secret) { 
 String format = "otpauth://totp/%s&#63;secret=%s"; 
 return String.format(format, user, secret); 
 } 
 
 /** 
 * Check the code entered by the user to see if it is valid 驗證code是否合法 
 * 
 * @param secret 
 *  The users secret. 
 * @param code 
 *  The code displayed on the users device 
 * @param t 
 *  The time in msec (System.currentTimeMillis() for example) 
 * @return 
 */ 
 public boolean check_code(String secret, long code, long timeMsec) { 
 Base32 codec = new Base32(); 
 byte[] decodedKey = codec.decode(secret); 
 // convert unix msec time into a 30 second "window" 
 // this is per the TOTP spec (see the RFC for details) 
 long t = (timeMsec / 1000L) / 30L; 
 // Window is used to check codes generated in the near past. 
 // You can use this value to tune how far you're willing to go. 
 for (int i = -window_size; i <= window_size; ++i) { 
  long hash; 
  try { 
  hash = verify_code(decodedKey, t + i); 
  } catch (Exception e) { 
  // Yes, this is bad form - but 
  // the exceptions thrown would be rare and a static 
  // configuration problem 
  e.printStackTrace(); 
  throw new RuntimeException(e.getMessage()); 
  // return false; 
  } 
  if (hash == code) { 
  return true; 
  } 
 } 
 // The validation code is invalid. 
 return false; 
 } 
 
 private static int verify_code(byte[] key, long t) throws NoSuchAlgorithmException, InvalidKeyException { 
 byte[] data = new byte[8]; 
 long value = t; 
 for (int i = 8; i-- > 0; value >>>= 8) { 
  data[i] = (byte) value; 
 } 
 SecretKeySpec signKey = new SecretKeySpec(key, "HmacSHA1"); 
 Mac mac = Mac.getInstance("HmacSHA1"); 
 mac.init(signKey); 
 byte[] hash = mac.doFinal(data); 
 int offset = hash[20 - 1] & 0xF; 
 // We're using a long because Java hasn't got unsigned int. 
 long truncatedHash = 0; 
 for (int i = 0; i < 4; ++i) { 
  truncatedHash <<= 8; 
  // We are dealing with signed bytes: 
  // we just keep the first byte. 
  truncatedHash |= (hash[offset + i] & 0xFF); 
 } 
 truncatedHash &= 0x7FFFFFFF; 
 truncatedHash %= 1000000; 
 return (int) truncatedHash; 
 } 
} 

package com.auth.google; 
 
import org.junit.Test; 
 
/** 
 * 
 * 
 * 身份認證測試 
 * 
 * @author yangbo 
 * 
 * @version 創建時間：2017年8月14日 上午11:09:23 
 * 
 * 
 */ 
public class AuthTest { 
 //當測試authTest時候，把genSecretTest生成的secret值賦值給它 
 private static String secret="R2Q3S52RNXBTFTOM"; 
 
 //@Test 
 public void genSecretTest() {// 生成密鑰 
  secret = GoogleAuthenticator.generateSecretKey(); 
 // 把這個qrcode生成二維碼，用google身份驗證器掃描二維碼就能添加成功 
 String qrcode = GoogleAuthenticator.getQRBarcode("2816661736@qq.com", secret); 
 System.out.println("qrcode:" + qrcode + ",key:" + secret); 
 } 
 /** 
 * 對app的隨機生成的code,輸入并驗證 
 */ 
 @Test 
 public void verifyTest() { 
 long code = 807337; 
 long t = System.currentTimeMillis(); 
 GoogleAuthenticator ga = new GoogleAuthenticator(); 
 ga.setWindowSize(5); 
 boolean r = ga.check_code(secret, code, t); 
 System.out.println("檢查code是否正確？" + r); 
 } 
}