001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.shiro.crypto;
020
021import org.apache.shiro.util.ByteSource;
022
023/**
024 * A component that can generate random number/byte values as needed.  Useful in cryptography or security scenarios
025 * where random byte arrays are needed, such as for password salts, nonces, initialization vectors and other seeds.
026 * <p/>
027 * This is essentially the same as a {@link java.security.SecureRandom SecureRandom}, and indeed implementations
028 * of this interface will probably all use {@link java.security.SecureRandom SecureRandom} instances, but this
029 * interface provides a few additional benefits to end-users:
030 * <ul>
031 * <li>It is an interface rather than the JDK's {@code SecureRandom} concrete implementation.  Implementation details
032 * can be customized as necessary based on the application's needs</li>
033 * <li>Default per-instance behavior can be customized on implementations, typically via JavaBeans mutators.</li>
034 * <li>Perhaps most important for Shiro end-users, tt can more easily be used as a source of cryptographic seed data,
035 * and the data returned is already in a more convenient {@link ByteSource ByteSource} format in case that data needs
036 * to be {@link org.apache.shiro.util.ByteSource#toHex() hex} or
037 * {@link org.apache.shiro.util.ByteSource#toBase64() base64}-encoded.</li>
038 * </ul>
039 * For example, consider the following example generating password salts for new user accounts:
040 * <pre>
041 * RandomNumberGenerator saltGenerator = new {@link org.apache.shiro.crypto.SecureRandomNumberGenerator SecureRandomNumberGenerator}();
042 * User user = new User();
043 * user.setPasswordSalt(saltGenerator.nextBytes().toBase64());
044 * userDAO.save(user);
045 * </pre>
046 *
047 * @since 1.1
048 */
049public interface RandomNumberGenerator {
050
051    /**
052     * Generates a byte array of fixed length filled with random data, often useful for generating salts,
053     * initialization vectors or other seed data.  The length is specified as a configuration
054     * value on the underlying implementation.
055     * <p/>
056     * If you'd like per-invocation control the number of bytes generated, use the
057     * {@link #nextBytes(int) nextBytes(int)} method instead.
058     *
059     * @return a byte array of fixed length filled with random data.
060     * @see #nextBytes(int)
061     */
062    ByteSource nextBytes();
063
064    /**
065     * Generates a byte array of the specified length filled with random data.
066     *
067     * @param numBytes the number of bytes to be populated with random data.
068     * @return a byte array of the specified length filled with random data.
069     * @see #nextBytes()
070     */
071    ByteSource nextBytes(int numBytes);
072}