LinuxSecureRandom.java

/*
 * Copyright 2014 http://Bither.net
 *
 * 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.
 *
 * Copyright 2013 Google Inc.
 *
 * 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 net.bither.xrandom;


import java.io.*;
import java.security.Provider;
import java.security.SecureRandomSpi;
import java.security.Security;

/**
 * A SecureRandom implementation that is able to override the standard JVM
 * provided implementation, and which simply serves random numbers by reading
 * /dev/urandom. That is, it delegates to the kernel on UNIX systems and is
 * unusable on other platforms. Attempts to manually set the seed are ignored.
 * There is no difference between seed bytes and non-seed bytes, they are all
 * from the same source.
 */
public class LinuxSecureRandom extends SecureRandomSpi {
    private static final FileInputStream urandom;

    private static class LinuxSecureRandomProvider extends Provider {
        public LinuxSecureRandomProvider() {
            super("LinuxSecureRandom", 1.0,
                    "A Linux specific random number provider that uses /dev/urandom");
            put("SecureRandom.LinuxSecureRandom",
                    LinuxSecureRandom.class.getName());
        }
    }

    static {
        try {
            File file = new File("/dev/urandom");
            if (file.exists()) {
                // This stream is deliberately leaked.
                urandom = new FileInputStream(file);
                // Now override the default SecureRandom implementation with
                // this one.
                Security.insertProviderAt(new LinuxSecureRandomProvider(), 1);
            } else {
                urandom = null;
            }
        } catch (FileNotFoundException e) {
            // Should never happen.
            throw new RuntimeException(e);
        }
    }

    private final DataInputStream dis;

    public LinuxSecureRandom() {
        // DataInputStream is not thread safe, so each random object has its
        // own.
        dis = new DataInputStream(urandom);
    }

    @Override
    protected void engineSetSeed(byte[] bytes) {
        // Ignore.
    }

    @Override
    protected void engineNextBytes(byte[] bytes) {
        try {
            System.out.println(LinuxSecureRandom.class.getSimpleName() + "LinuxSecureRandom get " + bytes.length + " bytes");
            dis.readFully(bytes); // This will block until all the bytes can be
            // read.
        } catch (IOException e) {
            throw new RuntimeException(e); // Fatal error. Do not attempt to
            // recover from this.
        }
    }

    @Override
    protected byte[] engineGenerateSeed(int i) {
        byte[] bits = new byte[i];
        engineNextBytes(bits);
        return bits;
    }
}