TOTP 概念
TOTP - Time-based One-time Password Algorithm is an extension of the HMAC-based One Time Password algorithm HOTP to support a time based moving factor.
TOTP（基于时间的一次性密码算法）是支持时间作为动态因素基于HMAC一次性密码算法的扩展。它是OTP算法的一种
算法如下: TOTP = Truncate(HMAC-SHA-1(K, (T - T0) / X))
K 共享密钥 T 时间 T0 开始计数的时间步长 X 时间步长
代码实现
最简实现需要如下两个类 1.Base32.java
public class Base32 {
private static final char[] ALPHABET = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '2', '3', '4', '5', '6', '7' };
private static final byte[] DECODE_TABLE;
static {
DECODE_TABLE = new byte[128];
for (int i = 0; i < DECODE_TABLE.length; i++) {
DECODE_TABLE[i] = (byte) 0xFF;
}
for (int i = 0; i < ALPHABET.length; i++) {
DECODE_TABLE[(int) ALPHABET[i]] = (byte) i;
if (i < 24) {
DECODE_TABLE[(int) Character.toLowerCase(ALPHABET[i])] = (byte) i;
}
}
}
public static String encode(byte[] data) {
char[] chars = new char[((data.length * 8) / 5) + ((data.length % 5) != 0 ? 1 : 0)];
for (int i = 0, j = 0, index = 0; i < chars.length; i++) {
if (index > 3) {
int b = data[j] & (0xFF >> index);
index = (index + 5) % 8;
b <<= index;
if (j < data.length - 1) {
b |= (data[j + 1] & 0xFF) >> (8 - index);
}
chars[i] = ALPHABET[b];
j++;
} else {
chars[i] = ALPHABET[((data[j] >> (8 - (index + 5))) & 0x1F)];
index = (index + 5) % 8;
if (index == 0) {
j++;
}
}
}
return new String(chars);
}
public static byte[] decode(String s) throws Exception {
char[] stringData = s.toCharArray();
byte[] data = new byte[(stringData.length * 5) / 8];
for (int i = 0, j = 0, index = 0; i < stringData.length; i++) {
int val;
try {
val = DECODE_TABLE[stringData[i]];
} catch (ArrayIndexOutOfBoundsException e) {
throw new Exception("Illegal character");
}
if (val == 0xFF) {
throw new Exception("Illegal character");
}
if (index <= 3) {
index = (index + 5) % 8;
if (index == 0) {
data[j++] |= val;
} else {
data[j] |= val << (8 - index);
}
} else {
index = (index + 5) % 8;
data[j++] |= (val >> index);
if (j < data.length) {
data[j] |= val << (8 - index);
}
}
}
return data;
}
}
2.GoogleAuthenticator.java
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Base64;
import javax.crypto.Mac;
public class GoogleAuthenticator {
// taken from Google pam docs - we probably don't need to mess with these
public static final int SECRET_SIZE = 10;
public static final String SEED = "g8GjEvTbW5oVSV7avLBdwIHqGlUYNzKFI7izOF8GwLDVKs2m0QN7vxRs2im5MDaNCWGmcD2rvcZx";
public static final String RANDOM_NUMBER_ALGORITHM = "SHA1PRNG";
int window_size = 3; // default 3 - max 17 (from google docs)最多可偏移的时间
/**
* 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.
* @return secret key
*/
public static String generateSecretKey() {
SecureRandom sr = null;
try {
sr = SecureRandom.getInstance(RANDOM_NUMBER_ALGORITHM);
sr.setSeed(Base64.getDecoder().decode(SEED));
byte[] buffer = sr.generateSeed(SECRET_SIZE);
Base32 codec = new Base32();
byte[] bEncodedKey = codec.encode(buffer).getBytes();
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 = "https://www.google.com/chart?chs=200x200&chld=M%%7C0&cht=qr&chl=otpauth://totp/%s@%s%%3Fsecret%%3D%s";
return String.format(format, user, host, secret);
}
/**
* Check the code entered by the user to see if it is valid
* @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
* @throws Exception
*/
public boolean check_code(String secret, long code, long timeMsec) throws Exception {
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;
}
}
测试类如下:
import org.junit.Test;
public class GoogleAuthTest {
@Test
public void genSecretTest() {
String secret = GoogleAuthenticator.generateSecretKey();
System.out.println("secret="+secret);
String url = GoogleAuthenticator.getQRBarcodeURL("testuser", "testhost", secret);
System.out.println("Please register " + url);
System.out.println("Secret key is " + secret);
}
// Change this to the saved secret from the running the above test.
static String savedSecret = "VGH25A7M54QPME5F";
@Test
public void authTest() throws Exception {
// enter the code shown on device. Edit this and run it fast before the code expires!
long code = 146841;
long t = System.currentTimeMillis();
GoogleAuthenticator ga = new GoogleAuthenticator();
ga.setWindowSize(5); //should give 5 * 30 seconds of grace...
boolean r = ga.check_code(savedSecret, code, t);
System.out.println("Check code = " + r);
}
}
OTP Auth协议
在实际使用中,通常把secret嵌入一段URL中并以二维码的形式发布,这个URL一般称为otpauth协议.其URL如下所示: otpauth://totp/testuser@testhost?secret=VGH25A7M54QPME5F&algorithm=SHA1&digits=6&period=30