/*
 * =============================================================================
 * 
 *   Copyright (c) 2019, The JASYPT team (http://www.jasypt.org)
 * 
 *   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.jasypt.iv;

import org.jasypt.exceptions.EncryptionInitializationException;

import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

 This implementation of IvGenerator holds a secure random
generator which can be used for generating random initialization vectors (IV) for encryption.


The algorithm used for random number generation can be configured at 
instantiation time. If not, the default algorithm will be used.


This class is thread-safe.

Author:
Hoki Torres
Since:
1.9.3/**
 * <p>
 * This implementation of {@link IvGenerator} holds a <b>secure</b> random
 * generator which can be used for generating random initialization vectors (IV) for encryption.
 * </p>
 * <p>
 * The algorithm used for random number generation can be configured at 
 * instantiation time. If not, the default algorithm will be used.
 * </p>
 * <p>
 * This class is <i>thread-safe</i>.
 * </p>
 * 
 * @since 1.9.3
 * 
 * @author Hoki Torres
 * 
 */
public class RandomIvGenerator implements IvGenerator {

    
The default algorithm to be used for secure random number
generation: set to SHA1PRNG.
/**
     * The default algorithm to be used for secure random number
     * generation: set to SHA1PRNG.
     */
    public static final String DEFAULT_SECURE_RANDOM_ALGORITHM = "SHA1PRNG";

    private final SecureRandom random;


    
Creates a new instance of RandomIvGenerator using the
default secure random number generation algorithm.
/**
     * Creates a new instance of <tt>RandomIvGenerator</tt> using the
     * default secure random number generation algorithm.
     */
    public RandomIvGenerator() {
        this(DEFAULT_SECURE_RANDOM_ALGORITHM);
    }


    
Creates a new instance of RandomIvGenerator specifying a
secure random number generation algorithm.
/**
     * Creates a new instance of <tt>RandomIvGenerator</tt> specifying a
     * secure random number generation algorithm.
     */
    public RandomIvGenerator(final String secureRandomAlgorithm) {
        super();
        try {
            this.random = SecureRandom.getInstance(secureRandomAlgorithm);
        } catch (NoSuchAlgorithmException e) {
            throw new EncryptionInitializationException(e);
        }
    }
    

    
Generate a random IV of the specified length in bytes.
Params:
lengthBytes – length in bytes.
Returns:
the generated IV./**
     * Generate a random IV of the specified length in bytes.
     * 
     * @param lengthBytes length in bytes.
     * @return the generated IV.
     */
    public byte[] generateIv(final int lengthBytes) {
        final byte[] iv = new byte[lengthBytes];
        synchronized (this.random) {
            this.random.nextBytes(iv);
        }
        return iv;
    }


    
This IV generator needs the IV to be included unencrypted in
encryption results, because of its being random. This method will always 
return true.
Returns:
true/**
     * This IV generator needs the IV to be included unencrypted in
     * encryption results, because of its being random. This method will always 
     * return true.
     * 
     * @return true
     */
    public boolean includePlainIvInEncryptionResults() {
        return true;
    }

    
}