/*
 * Copyright 2011-2016 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.encrypt;

import org.springframework.security.crypto.encrypt.AesBytesEncryptor.CipherAlgorithm;
import org.springframework.security.crypto.keygen.KeyGenerators;

/**
 * Factory for commonly used encryptors. Defines the public API for constructing
 * {@link BytesEncryptor} and {@link TextEncryptor} implementations.
 *
 * @author Keith Donald
 */
public class Encryptors {

	/**
	 * Creates a standard password-based bytes encryptor using 256 bit AES encryption with
	 * Galois Counter Mode (GCM). Derives the secret key using PKCS #5's PBKDF2
	 * (Password-Based Key Derivation Function #2). Salts the password to prevent
	 * dictionary attacks against the key. The provided salt is expected to be
	 * hex-encoded; it should be random and at least 8 bytes in length. Also applies a
	 * random 16 byte initialization vector to ensure each encrypted message will be
	 * unique. Requires Java 6.
	 *
	 * @param password the password used to generate the encryptor's secret key; should
	 * not be shared
	 * @param salt a hex-encoded, random, site-global salt value to use to generate the
	 * key
	 *
	 * @see #standard(CharSequence, CharSequence) which uses the slightly weaker CBC mode
	 * (instead of GCM)
	 */
	public static BytesEncryptor stronger(CharSequence password, CharSequence salt) {
		return new AesBytesEncryptor(password.toString(), salt,
				KeyGenerators.secureRandom(16), CipherAlgorithm.GCM);
	}

	/**
	 * Creates a standard password-based bytes encryptor using 256 bit AES encryption.
	 * Derives the secret key using PKCS #5's PBKDF2 (Password-Based Key Derivation
	 * Function #2). Salts the password to prevent dictionary attacks against the key. The
	 * provided salt is expected to be hex-encoded; it should be random and at least 8
	 * bytes in length. Also applies a random 16 byte initialization vector to ensure each
	 * encrypted message will be unique. Requires Java 6.
	 *
	 * @param password the password used to generate the encryptor's secret key; should
	 * not be shared
	 * @param salt a hex-encoded, random, site-global salt value to use to generate the
	 * key
	 */
	public static BytesEncryptor standard(CharSequence password, CharSequence salt) {
		return new AesBytesEncryptor(password.toString(), salt,
				KeyGenerators.secureRandom(16));
	}

	/**
	 * Creates a text encryptor that uses "stronger" password-based encryption. Encrypted
	 * text is hex-encoded.
	 *
	 * @param password the password used to generate the encryptor's secret key; should
	 * not be shared
	 * @see Encryptors#stronger(CharSequence, CharSequence)
	 */
	public static TextEncryptor delux(CharSequence password, CharSequence salt) {
		return new HexEncodingTextEncryptor(stronger(password, salt));
	}

	/**
	 * Creates a text encryptor that uses "standard" password-based encryption. Encrypted
	 * text is hex-encoded.
	 *
	 * @param password the password used to generate the encryptor's secret key; should
	 * not be shared
	 * @see Encryptors#standard(CharSequence, CharSequence)
	 */
	public static TextEncryptor text(CharSequence password, CharSequence salt) {
		return new HexEncodingTextEncryptor(standard(password, salt));
	}

	/**
	 * Creates an encryptor for queryable text strings that uses standard password-based
	 * encryption. Uses a 16-byte all-zero initialization vector so encrypting the same
	 * data results in the same encryption result. This is done to allow encrypted data to
	 * be queried against. Encrypted text is hex-encoded.
	 *
	 * @param password the password used to generate the encryptor's secret key; should
	 * not be shared
	 * @param salt a hex-encoded, random, site-global salt value to use to generate the
	 * secret key
	 */
	public static TextEncryptor queryableText(CharSequence password, CharSequence salt) {
		return new HexEncodingTextEncryptor(new AesBytesEncryptor(password.toString(),
				salt));
	}

	/**
	 * Creates a text encryptor that performs no encryption. Useful for developer testing
	 * environments where working with plain text strings is desired for simplicity.
	 */
	public static TextEncryptor noOpText() {
		return NO_OP_TEXT_INSTANCE;
	}

	private Encryptors() {
	}

	private static final TextEncryptor NO_OP_TEXT_INSTANCE = new NoOpTextEncryptor();

	private static final class NoOpTextEncryptor implements TextEncryptor {

		public String encrypt(String text) {
			return text;
		}

		public String decrypt(String encryptedText) {
			return encryptedText;
		}

	}

}
