/*
 * Copyright 2002-2017 the original author or authors.
 *
 * 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 org.springframework.security.crypto.scrypt;

import java.util.Base64;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.bouncycastle.crypto.generators.SCrypt;
import org.springframework.security.crypto.codec.Utf8;
import org.springframework.security.crypto.keygen.BytesKeyGenerator;
import org.springframework.security.crypto.keygen.KeyGenerators;
import org.springframework.security.crypto.password.PasswordEncoder;

/**
 * <p>
 * Implementation of PasswordEncoder that uses the SCrypt hashing function.
 * Clients can optionally supply a cpu cost parameter, a memory cost parameter
 * and a parallelization parameter.
 * </p>
 *
 * <p>
 * A few <a href=
 * "http://bouncy-castle.1462172.n4.nabble.com/Java-Bouncy-Castle-scrypt-implementation-td4656832.html">
 * warnings</a>:
 * </p>
 *
 * <ul>
 * <li>The currently implementation uses Bouncy castle which does not exploit
 * parallelism/optimizations that password crackers will, so there is an
 * unnecessary asymmetry between attacker and defender.</li>
 * <li>Scrypt is based on Salsa20 which performs poorly in Java (on par with
 * AES) but performs awesome (~4-5x faster) on SIMD capable platforms</li>
 * <li>While there are some that would disagree, consider reading -
 * <a href="http://blog.ircmaxell.com/2014/03/why-i-dont-recommend-scrypt.html">
 * Why I Don't Recommend Scrypt</a> (for password storage)</li>
 * </ul>
 *
 * @author Shazin Sadakath
 * @author Rob Winch
 *
 */
public class SCryptPasswordEncoder implements PasswordEncoder {

	private final Log logger = LogFactory.getLog(getClass());

	private final int cpuCost;

	private final int memoryCost;

	private final int parallelization;

	private final int keyLength;

	private final BytesKeyGenerator saltGenerator;

	public SCryptPasswordEncoder() {
		this(16384, 8, 1, 32, 64);
	}

	/**
	 * Creates a new instance
	 *
	 * @param cpuCost
	 *            cpu cost of the algorithm (as defined in scrypt this is N).
	 *            must be power of 2 greater than 1. Default is currently 16,348
	 *            or 2^14)
	 * @param memoryCost
	 *            memory cost of the algorithm (as defined in scrypt this is r)
	 *            Default is currently 8.
	 * @param parallelization
	 *            the parallelization of the algorithm (as defined in scrypt
	 *            this is p) Default is currently 1. Note that the
	 *            implementation does not currently take advantage of
	 *            parallelization.
	 * @param keyLength
	 *            key length for the algorithm (as defined in scrypt this is
	 *            dkLen). The default is currently 32.
	 * @param saltLength
	 *            salt length (as defined in scrypt this is the length of S).
	 *            The default is currently 64.
	 */
	public SCryptPasswordEncoder(int cpuCost, int memoryCost, int parallelization, int keyLength, int saltLength) {
		if (cpuCost <= 1) {
			throw new IllegalArgumentException("Cpu cost parameter must be > 1.");
		}
		if (memoryCost == 1 && cpuCost > 65536) {
			throw new IllegalArgumentException("Cpu cost parameter must be > 1 and < 65536.");
		}
		if (memoryCost < 1) {
			throw new IllegalArgumentException("Memory cost must be >= 1.");
		}
		int maxParallel = Integer.MAX_VALUE / (128 * memoryCost * 8);
		if (parallelization < 1 || parallelization > maxParallel) {
			throw new IllegalArgumentException("Parallelisation parameter p must be >= 1 and <= " + maxParallel
					+ " (based on block size r of " + memoryCost + ")");
		}
		if (keyLength < 1 || keyLength > Integer.MAX_VALUE) {
			throw new IllegalArgumentException("Key length must be >= 1 and <= " + Integer.MAX_VALUE);
		}
		if (saltLength < 1 || saltLength > Integer.MAX_VALUE) {
			throw new IllegalArgumentException("Salt length must be >= 1 and <= " + Integer.MAX_VALUE);
		}

		this.cpuCost = cpuCost;
		this.memoryCost = memoryCost;
		this.parallelization = parallelization;
		this.keyLength = keyLength;
		this.saltGenerator = KeyGenerators.secureRandom(saltLength);
	}

	public String encode(CharSequence rawPassword) {
		return digest(rawPassword, saltGenerator.generateKey());
	}

	public boolean matches(CharSequence rawPassword, String encodedPassword) {
		if (encodedPassword == null || encodedPassword.length() < keyLength) {
			logger.warn("Empty encoded password");
			return false;
		}
		return decodeAndCheckMatches(rawPassword, encodedPassword);
	}

	private boolean decodeAndCheckMatches(CharSequence rawPassword, String encodedPassword) {
		String[] parts = encodedPassword.split("\\$");

		if (parts.length != 4) {
			return false;
		}

		long params = Long.parseLong(parts[1], 16);
		byte[] salt = decodePart(parts[2]);
		byte[] derived = decodePart(parts[3]);

		int cpuCost = (int) Math.pow(2, params >> 16 & 0xffff);
		int memoryCost = (int) params >> 8 & 0xff;
		int parallelization = (int) params & 0xff;

		byte[] generated = SCrypt.generate(Utf8.encode(rawPassword), salt, cpuCost, memoryCost, parallelization,
				keyLength);

		if (derived.length != generated.length) {
			return false;
		}

		int result = 0;
		for (int i = 0; i < derived.length; i++) {
			result |= derived[i] ^ generated[i];
		}
		return result == 0;
	}

	private String digest(CharSequence rawPassword, byte[] salt) {
		byte[] derived = SCrypt.generate(Utf8.encode(rawPassword), salt, cpuCost, memoryCost, parallelization, keyLength);

		String params = Long
				.toString(((int) (Math.log(cpuCost) / Math.log(2)) << 16L) | memoryCost << 8 | parallelization, 16);

		StringBuilder sb = new StringBuilder((salt.length + derived.length) * 2);
		sb.append("$").append(params).append('$');
		sb.append(encodePart(salt)).append('$');
		sb.append(encodePart(derived));

		return sb.toString();
	}

	private byte[] decodePart(String part) {
		return Base64.getDecoder().decode(Utf8.encode(part));
	}

	private String encodePart(byte[] part) {
		return Utf8.decode(Base64.getEncoder().encode(part));
	}
}
