package util;
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import java.security.InvalidKeyException;
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import java.security.NoSuchAlgorithmException;
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import java.security.SecureRandom;
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import javax.crypto.Mac;
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import javax.crypto.spec.SecretKeySpec;
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import org.apache.commons.codec.binary.Base32;
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import org.apache.commons.codec.binary.Base64;
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/**
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* Java Server side class for Google Authenticator's TOTP generator Thanks to
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* Enrico's blog for the sample code:
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*
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* @see http://thegreyblog.blogspot.com/2011/12/google-authenticator-using-it-in-your.html
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* @see http://code.google.com/p/google-authenticator
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* @see http://tools.ietf.org/id/draft-mraihi-totp-timebased-06.txt
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*/
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public class GoogleAuthenticator {
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// taken from Google pam docs - we probably don't need to mess with these
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public static final int SECRET_SIZE = 10;
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public static final String SEED = "H8GjEvTbW5oVSV7avFDdwIHqGlUYNzKFI7izOF8GwGEKIs2mEdN7vxRs2im5REaNCWGmcD2rvTex";
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public static final String RANDOM_NUMBER_ALGORITHM = "SHA1PRNG";
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int window_size = 3; // default 3 - max 17 (from google docs)最多可偏移的时间
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/**
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* set the windows size. This is an integer value representing the number of 30
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* second windows we allow The bigger the window, the more tolerant of clock
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* skew we are.
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*
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* @param s window size - must be >=1 and <=17. Other values are ignored
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*/
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public void setWindowSize(int s) {
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if (s >= 1 && s <= 17)
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window_size = s;
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}
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/**
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* Generate a random secret key. This must be saved by the server and associated
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* with the users account to verify the code displayed by Google Authenticator.
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* The user must register this secret on their device.
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*
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* @return secret key
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*/
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public static String generateSecretKey() {
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SecureRandom sr = null;
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try {
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sr = SecureRandom.getInstance(RANDOM_NUMBER_ALGORITHM);
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sr.setSeed(Base64.decodeBase64(SEED));
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byte[] buffer = sr.generateSeed(SECRET_SIZE);
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Base32 codec = new Base32();
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byte[] bEncodedKey = codec.encode(buffer);
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String encodedKey = new String(bEncodedKey);
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return encodedKey;
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} catch (NoSuchAlgorithmException e) {
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// should never occur... configuration error
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}
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return null;
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}
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/**
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* Return a URL that generates and displays a QR barcode. The user scans this
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* bar code with the Google Authenticator application on their smartphone to
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* register the auth code. They can also manually enter the secret if desired
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*
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* @param user user id (e.g. fflinstone)
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* @param host host or system that the code is for (e.g. myapp.com)
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* @param secret the secret that was previously generated for this user
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* @return the URL for the QR code to scan
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*/
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public static String getQRBarcodeURL(String user, String host, String secret) {
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String format = "https://www.google.com/chart?chs=200x200&chld=M%%7C0&cht=qr&chl=otpauth://totp/%s@%s%%3Fsecret%%3D%s";
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return String.format(format, user, host, secret);
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}
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/**
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* Check the code entered by the user to see if it is valid
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*
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* @param secret The users secret.
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* @param code The code displayed on the users device
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* @param t The time in msec (System.currentTimeMillis() for example)
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* @return
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*/
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public boolean check_code(String secret, long code, long timeMsec) {
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Base32 codec = new Base32();
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byte[] decodedKey = codec.decode(secret);
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// convert unix msec time into a 30 second "window"
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// this is per the TOTP spec (see the RFC for details)
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long t = (timeMsec / 1000L) / 30L;
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// Window is used to check codes generated in the near past.
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// You can use this value to tune how far you're willing to go.
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for (int i = -window_size; i <= window_size; ++i) {
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long hash;
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try {
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hash = verify_code(decodedKey, t + i);
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} catch (Exception e) {
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// Yes, this is bad form - but
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// the exceptions thrown would be rare and a static configuration problem
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e.printStackTrace();
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throw new RuntimeException(e.getMessage());
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// return false;
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}
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if (hash == code) {
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return true;
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}
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}
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// The validation code is invalid.
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return false;
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}
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private static int verify_code(byte[] key, long t) throws NoSuchAlgorithmException, InvalidKeyException {
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byte[] data = new byte[8];
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long value = t;
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for (int i = 8; i-- > 0; value >>>= 8) {
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data[i] = (byte) value;
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}
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SecretKeySpec signKey = new SecretKeySpec(key, "HmacSHA1");
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Mac mac = Mac.getInstance("HmacSHA1");
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mac.init(signKey);
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byte[] hash = mac.doFinal(data);
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int offset = hash[20 - 1] & 0xF;
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// We're using a long because Java hasn't got unsigned int.
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long truncatedHash = 0;
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for (int i = 0; i < 4; ++i) {
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truncatedHash <<= 8;
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// We are dealing with signed bytes:
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// we just keep the first byte.
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truncatedHash |= (hash[offset + i] & 0xFF);
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}
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truncatedHash &= 0x7FFFFFFF;
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truncatedHash %= 1000000;
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return (int) truncatedHash;
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}
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}
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