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/*
 * Copyright 2017 ~ 2025 the original author or authors. James Wong 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.wl4g.infra.common.crypto.hmac;

import static com.wl4g.infra.common.lang.Assert2.hasTextOf;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

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

/**
 * PBKDF2 deriveKey utility.
 * 
 * @author James Wong James Wong 
 * @version v1.0 2019年1月20日
 * @since
 */
public class Pbkdf2Utils {

    /**
     * Calculate pbkdf2 value.
     * 
     * @param password
     * @param salt
     * @param iterations
     * @param dkLen
     * @return
     * @throws InvalidKeyException
     * @throws NoSuchAlgorithmException
     */
    public static String pbkdf2(String password, String salt, int iterations, int dkLen)
            throws InvalidKeyException, NoSuchAlgorithmException {
        hasTextOf(password, "Password");
        hasTextOf(salt, "Salt");

        if (dkLen != 16 && dkLen != 24 && dkLen != 32) {
            dkLen = 16;
        }
        if (iterations < 0) {
            iterations = 0;
        }

        byte[] _password = password.getBytes();
        byte[] _salt = salt.getBytes();
        byte[] key = Pbkdf2Utils.deriveKey(_password, _salt, iterations, dkLen);
        return new String(key);
    }

    private static byte[] deriveKey(byte[] password, byte[] salt, int iterationCount, int dkLen)
            throws NoSuchAlgorithmException, InvalidKeyException {
        SecretKeySpec keyspec = new SecretKeySpec(password, "HmacSHA256");
        Mac prf = Mac.getInstance("HmacSHA256");
        prf.init(keyspec);

        // Note: hLen, dkLen, l, r, T, F, etc. are horrible names for
        // variables and functions in this day and age, but they
        // reflect the terse symbols used in RFC 2898 to describe
        // the PBKDF2 algorithm, which improves validation of the
        // code vs. the RFC.
        //
        // dklen is expressed in bytes. (16 for a 128-bit key)

        int hLen = prf.getMacLength(); // 20 for SHA1
        int l = Math.max(dkLen, hLen); // 1 for 128bit (16-byte) keys
        int r = dkLen - (l - 1) * hLen; // 16 for 128bit (16-byte) keys
        byte T[] = new byte[l * hLen];
        int ti_offset = 0;
        for (int i = 1; i <= l; i++) {
            F(T, ti_offset, prf, salt, iterationCount, i);
            ti_offset += hLen;
        }

        if (r < hLen) {
            // Incomplete last block
            byte DK[] = new byte[dkLen];
            System.arraycopy(T, 0, DK, 0, dkLen);
            return DK;
        }
        return T;
    }

    private static void F(byte[] dest, int offset, Mac prf, byte[] S, int c, int blockIndex) {
        final int hLen = prf.getMacLength();
        byte U_r[] = new byte[hLen];
        // U0 = S || INT (i);
        byte U_i[] = new byte[S.length + 4];
        System.arraycopy(S, 0, U_i, 0, S.length);
        INT(U_i, S.length, blockIndex);
        for (int i = 0; i < c; i++) {
            U_i = prf.doFinal(U_i);
            xor(U_r, U_i);
        }

        System.arraycopy(U_r, 0, dest, offset, hLen);
    }

    private static void xor(byte[] dest, byte[] src) {
        for (int i = 0; i < dest.length; i++) {
            dest[i] ^= src[i];
        }
    }

    private static void INT(byte[] dest, int offset, int i) {
        dest[offset + 0] = (byte) (i / (256 * 256 * 256));
        dest[offset + 1] = (byte) (i / (256 * 256));
        dest[offset + 2] = (byte) (i / (256));
        dest[offset + 3] = (byte) (i);
    }

}