RandomBytesGenerator.java

/*
 * Copyright 2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except
 * in compliance with the License. A copy of the License is located at
 *
 * http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.encryptionsdk.internal;

import java.security.SecureRandom;

public class RandomBytesGenerator {
    private static final SecureRandom RND = new SecureRandom();

    /* Some Providers (such as the FIPS certified Bouncy Castle) enforce a
     * maximum number of bytes that may be requested from SecureRandom. If
     * the requested len is larger than this value, the Secure Random will
     * be called multiple times to achieve the requested total length. */
    private static final int MAX_BYTES = 1 << 15;

    /**
     * Generates a byte array of random data of the given length.
     *
     * @param len The length of the byte array.
     * @return The byte array.
     */
    public static byte[] generate(final int len) {
        final byte[] result = new byte[len];
        int bytesGenerated = 0;

        while (bytesGenerated < len) {
            final int requestSize = Math.min(MAX_BYTES, len - bytesGenerated);
            final byte[] request = new byte[requestSize];
            RND.nextBytes(request);
            System.arraycopy(request, 0, result, bytesGenerated, requestSize);
            bytesGenerated += requestSize;
        }

        return result;
    }

}