/*
 * Copyright 2002-2018 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
 *
 *      https://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.password;

import java.util.Base64;

import org.springframework.security.crypto.codec.Hex;
import org.springframework.security.crypto.codec.Utf8;
import org.springframework.security.crypto.keygen.Base64StringKeyGenerator;
import org.springframework.security.crypto.keygen.StringKeyGenerator;

/**
 * This {@link PasswordEncoder} is provided for legacy purposes only and is not considered
 * secure.
 *
 * Encodes passwords using MD4. The general format of the password is:
 *
 * <pre>
 * s = salt == null ? "" : "{" + salt + "}"
 * s + md4(password + s)
 * </pre>
 *
 * Such that "salt" is the salt, md4 is the digest method, and password is the actual
 * password. For example with a password of "password", and a salt of "thisissalt":
 *
 * <pre>
 * String s = salt == null ? "" : "{" + salt + "}";
 * s + md4(password + s)
 * "{thisissalt}" + md4(password + "{thisissalt}")
 * "{thisissalt}6cc7924dad12ade79dfb99e424f25260"
 * </pre>
 *
 * If the salt does not exist, then omit "{salt}" like this:
 *
 * <pre>
 * md4(password)
 * </pre>
 *
 * If the salt is an empty String, then only use "{}" like this:
 *
 * <pre>
 * "{}" + md4(password + "{}")
 * </pre>
 *
 * The format is intended to work with the Md4PasswordEncoder that was found in the Spring
 * Security core module. However, the passwords will need to be migrated to include any
 * salt with the password since this API provides Salt internally vs making it the
 * responsibility of the user. To migrate passwords from the SaltSource use the following:
 *
 * <pre>
 * String salt = saltSource.getSalt(user);
 * String s = salt == null ? null : "{" + salt + "}";
 * String migratedPassword = s + user.getPassword();
 * </pre>
 *
 * @author Ray Krueger
 * @author Luke Taylor
 * @author Rob winch
 * @since 5.0
 * @deprecated Digest based password encoding is not considered secure. Instead use an
 * adaptive one way function like BCryptPasswordEncoder, Pbkdf2PasswordEncoder, or
 * SCryptPasswordEncoder. Even better use {@link DelegatingPasswordEncoder} which supports
 * password upgrades. There are no plans to remove this support. It is deprecated to
 * indicate that this is a legacy implementation and using it is considered insecure.
 */
@Deprecated
public class Md4PasswordEncoder implements PasswordEncoder {

	private static final String PREFIX = "{";

	private static final String SUFFIX = "}";

	private StringKeyGenerator saltGenerator = new Base64StringKeyGenerator();

	private boolean encodeHashAsBase64;

	public void setEncodeHashAsBase64(boolean encodeHashAsBase64) {
		this.encodeHashAsBase64 = encodeHashAsBase64;
	}

	/**
	 * Encodes the rawPass using a MessageDigest. If a salt is specified it will be merged
	 * with the password before encoding.
	 * @param rawPassword The plain text password
	 * @return Hex string of password digest (or base64 encoded string if
	 * encodeHashAsBase64 is enabled.
	 */
	@Override
	public String encode(CharSequence rawPassword) {
		String salt = PREFIX + this.saltGenerator.generateKey() + SUFFIX;
		return digest(salt, rawPassword);
	}

	private String digest(String salt, CharSequence rawPassword) {
		if (rawPassword == null) {
			rawPassword = "";
		}
		String saltedPassword = rawPassword + salt;
		byte[] saltedPasswordBytes = Utf8.encode(saltedPassword);
		Md4 md4 = new Md4();
		md4.update(saltedPasswordBytes, 0, saltedPasswordBytes.length);
		byte[] digest = md4.digest();
		String encoded = encode(digest);
		return salt + encoded;
	}

	private String encode(byte[] digest) {
		if (this.encodeHashAsBase64) {
			return Utf8.decode(Base64.getEncoder().encode(digest));
		}
		return new String(Hex.encode(digest));
	}

	/**
	 * Takes a previously encoded password and compares it with a rawpassword after mixing
	 * in the salt and encoding that value
	 * @param rawPassword plain text password
	 * @param encodedPassword previously encoded password
	 * @return true or false
	 */
	@Override
	public boolean matches(CharSequence rawPassword, String encodedPassword) {
		String salt = extractSalt(encodedPassword);
		String rawPasswordEncoded = digest(salt, rawPassword);
		return PasswordEncoderUtils.equals(encodedPassword.toString(), rawPasswordEncoded);
	}

	private String extractSalt(String prefixEncodedPassword) {
		int start = prefixEncodedPassword.indexOf(PREFIX);
		if (start != 0) {
			return "";
		}
		int end = prefixEncodedPassword.indexOf(SUFFIX, start);
		if (end < 0) {
			return "";
		}
		return prefixEncodedPassword.substring(start, end + 1);
	}

}
