Java example source code file (StrongSeedReader.java)

This example Java source code file (StrongSeedReader.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

byte, exception, fileoutputstream, nativeprng, net, network, securerandom, security, sha1prng, strongseedreader, windows

The StrongSeedReader.java Java example source code

 /*
 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/**
 * @test
 * @bug 6425477
 * @summary Better support for generation of high entropy random numbers
 * @run main/othervm StrongSeedReader
 */

import java.io.*;
import java.net.*;
import java.security.SecureRandom;

/**
 * A simple test which takes into account knowledge about the underlying
 * implementation. This may change if the implementations change.
 *
 * Create a new EGD file with known bytes, then set the EGD System property. The
 * data read should be the same as what was written.
 */
public class StrongSeedReader {

    public static void main(String[] args) throws Exception {
        // Skip Windows, the SHA1PRNG uses CryptGenRandom.
        if (System.getProperty("os.name", "unknown").startsWith("Windows")) {
            return;
        }

        File file = null;
        try {
            file = new File(System.getProperty("java.io.tmpdir"),
                    "StrongSeedReader.tmpdata");

            // write a bunch of 0's to the file.
            FileOutputStream fos = new FileOutputStream(file);
            fos.write(new byte[2048]);

            System.setProperty("java.security.egd", file.toURI().toString());
            testSeed("NativePRNG");
            testSeed("SHA1PRNG");
        } finally {
            if (file != null) {
                file.delete();
            }
        }
    }

    private static void testSeed(String alg) throws Exception {
        System.out.println("Testing: " + alg);
        SecureRandom sr = SecureRandom.getInstance(alg);
        byte[] ba = sr.generateSeed(20);

        // We should get back a bunch of zeros from the file.
        for (byte b : ba) {
            if (b != 0) {
                throw new Exception("Byte != 0");
            }
        }
    }
}