TOTP.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 games647 and contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.github.games647.flexiblelogin.hasher;

import com.google.common.io.BaseEncoding;
import com.google.common.primitives.Ints;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Date;
import java.util.concurrent.TimeUnit;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class TOTP implements Hasher {

    private static final int SCRET_BYTE = 10;
    private static final int SCRATCH_CODES = 5;
    private static final int BYTES_PER_SCRATCH_CODE = 4;

    private static final int TIME_PRECISION = 3;
    private static final String CRYPTO_ALGO = "HmacSHA1";

    public static String generateSecretKey() {
        // Allocating the buffer
        byte[] buffer = new byte[SCRET_BYTE + SCRATCH_CODES * BYTES_PER_SCRATCH_CODE];

        // Filling the buffer with random numbers.
        // Notice: you want to reuse the same random generator
        // while generating larger random number sequences.
        new SecureRandom().nextBytes(buffer);

        // Getting the key and converting it to Base32
        byte[] secretKey = Arrays.copyOf(buffer, SCRET_BYTE);
        return BaseEncoding.base32().encode(secretKey);
    }

    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);
    }

    private static boolean check_code(String secret, long code, long time)
            throws NoSuchAlgorithmException, InvalidKeyException {
        byte[] decodedKey = BaseEncoding.base32().decode(secret);

        // 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.
        int window = TIME_PRECISION;
        for (int i = -window; i <= window; ++i) {
            long hash = verify_code(decodedKey, time + i);

            if (hash == code) {
                return true;
            }
        }

        // The validation code is invalid.
        return false;
    }

    private static int verify_code(byte[] key, long time) throws NoSuchAlgorithmException, InvalidKeyException {
        byte[] data = new byte[8];
        long value = time;
        for (int i = 8; i-- > 0; value >>>= 8) {
            data[i] = (byte) value;
        }

        SecretKeySpec signKey = new SecretKeySpec(key, CRYPTO_ALGO);
        Mac mac = Mac.getInstance(CRYPTO_ALGO);
        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 &= 0x7FFF_FFFF;
        truncatedHash %= 1_000_000;

        return (int) truncatedHash;
    }

    @Override
    public String hash(String rawPassword) {
        //it's the secret code. We need to save it here
        return generateSecretKey();
    }

    @Override
    public boolean checkPassword(String passwordHash, String userInput) throws Exception {
        Integer code = Ints.tryParse(userInput);
        if (code == null) {
            return false;
        }

        long currentTime = new Date().getTime() / TimeUnit.SECONDS.toMillis(30);
        return check_code(passwordHash, code, currentTime);
    }
}