google身份认证器服务端key的生成和它生成的随机密码的验证：
客户端和服务器事先协商好一个密钥K，用于一次性密码的生成过程，此密钥不被任何第三方所知道。此外，客户端和服务器各有一个计数器C，并且事先将计数值同步。进行验证时，客户端对密钥和计数器的组合(K,C)使用HMAC（Hash-based Message Authentication Code）算法计算一次性密码，公式如下：
上面采用了HMAC-SHA-1，当然也可以使用HMAC-MD5等。HMAC算法得出的值位数比较多，不方便用户输入，因此需要截断（Truncate）成为一组不太长十进制数（例如6位）。计算完成之后客户端计数器C计数值加1。用户将这一组十进制数输入并且提交之后，服务器端同样的计算，并且与用户提交的数值比较，如果相同，则验证通过，服务器端将计数值C增加1。如果不相同，则验证失败。
import java.security.InvalidKeyException;import java.security.NoSuchAlgorithmException;import java.security.SecureRandom;import javax.crypto.Mac;import javax.crypto.spec.SecretKeySpec;import mons.codec.binary.Base32;import mons.codec.binary.Base64;/*** google身份验证器，java服务端实现*/public class GoogleAuthenticator {// 生成的key长度( Generate secret key length)public static final int SECRET_SIZE = 10;public static final String SEED = "g8GjEvTbW5oVSV7avL47357438reyhreyuryetredLDVKs2m0QN7vxRs2im5MDaNCWGmcD2rvcZx";// Java实现随机数算法public static final String RANDOM_NUMBER_ALGORITHM = "SHA1PRNG";// 最多可偏移的时间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.* 生成一个随机秘钥** @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. )* @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 = "/chart?chs=200x200&chld=M%%7C0&cht=qr&chl=otpauth://totp/%s@%s?secret=%s";return String.format(format, user, host, secret);}/*** 生成一个google身份验证器，识别的字符串，只需要把该方法返回值生成二维码扫描就可以了。** @param user 账号* @param secret 密钥* @return*/public static String getQRBarcode(String user, String secret) {String format = "otpauth://totp/%s?secret=%s";return String.format(format, user, secret);}/*** Check the code entered by the user to see if it is valid 验证code是否合法** @param secret The users secret.* @param codeThe code displayed on the users device* @param timeMsec 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);System.out.println(hash);} catch (Exception e) {// Yes, this is bad form - but// the exceptions thrown would be rare and a static// configuration probleme.printStackTrace();throw new RuntimeException(e.getMessage());// return false;}System.out.println(code);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;}}
测试代码：
import org.junit.Test;/*** 身份认证测试*/public class AuthTest {//当测试authTest时候，把genSecretTest生成的secret值赋值给它private static String secret = "R2Q3S52RNXBTFTOM";//@Testpublic void genSecretTest() {// 生成密钥secret = GoogleAuthenticator.generateSecretKey();// 把这个qrcode生成二维码，用google身份验证器扫描二维码就能添加成功String qrcode = GoogleAuthenticator.getQRBarcode("2816661736@", secret);System.out.println("qrcode:" + qrcode + ",key:" + secret);}/*** 对app的随机生成的code,输入并验证*/@Testpublic 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("检查code是否正确？" + r);}}
具体使用方式(iOS演示)：
第一步：进入iphone的appstore，在搜索框中输入 google身份验证器，如下图：
选择上图中的 google authenticator 并安装。
第二步：运行下面链接中下载的demo中的 AuthTest 的 genSecretTest 方法，控制台打印的结果如下图：
key：为app与服务端约定的秘钥，用于双方的认证。
qrcode：是app扫码能够识别的就是二维码值，把它生成二维码如下图：
第三步:打开 google authenticator app 软件选择扫描条形码按扭打开相机对二维码扫描加入账号，如下图：
第四步：把 app 中的数字，在 AuthTest 的 verifyTest 进行验证，如下图：
