Generate UUIDs using urandom (nonblocking random number entropy)

DevUrandomSeedGenerator.java

// ============================================================================
//   Copyright 2006-2010 Daniel W. Dyer
//
//   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.
// ============================================================================
//
// The original file is part of the maths.uncommons.org project.
// This is modified to use /dev/urandom as its source of entropy.
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.uncommons.maths.random.SeedException;
import org.uncommons.maths.random.SeedGenerator;

/**
 * RNG seed strategy that gets data from {@literal /dev/urandom} on systems that
 * provide it (e.g. Solaris/Linux). If {@literal /dev/urandom} does not exist or
 * is not accessible, a {@link SeedException} is thrown.
 *
 * @author Daniel Dyer
 */
public class DevUrandomSeedGenerator implements SeedGenerator {
    private static final File DEV_URANDOM = new File("/dev/urandom");

    /**
     * {@inheritDoc}
     *
     * @return The requested number of random bytes, read directly from
     * {@literal /dev/urandom}.
     * @throws SeedException If {@literal /dev/urandom} does not exist or is not
     *                       accessible
     */
    @Override
    public byte[] generateSeed(int length) throws SeedException {
        try (FileInputStream file = new FileInputStream(DEV_URANDOM)) {
            byte[] randomSeed = new byte[length];
            int count = 0;
            while (count < length) {
                int bytesRead = file.read(randomSeed, count, length - count);
                if (bytesRead == -1) {
                    throw new SeedException("EOF encountered reading random data.");
                }
                count += bytesRead;
            }
            return randomSeed;
        } catch (IOException ex) {
            throw new SeedException("Failed reading from " + DEV_URANDOM.getName(), ex);
        } catch (SecurityException ex) {
            // Might be thrown if resource access is restricted (such as in
            // an applet sandbox).
            throw new SeedException("SecurityManager prevented access to " + DEV_URANDOM.getName(), ex);
        }
    }

    @Override
    public String toString() {
        return "/dev/urandom";
    }
}

UUIDGenerator.java

import java.security.GeneralSecurityException;
import java.util.Random;
import java.util.UUID;

import org.slf4j.LoggerFactory;
import org.uncommons.maths.random.AESCounterRNG;
import org.uncommons.maths.random.SeedException;

import com.fasterxml.uuid.Generators;
import com.fasterxml.uuid.impl.RandomBasedGenerator;



public enum UUIDgenerator {
    INSTANCE;
    private final RandomBasedGenerator rbg;
    
    @SuppressWarnings("FieldCanBeLocal")
    private final Random random = new Random();


    UUIDGenerator() {
        Random rng = random;
        try {
            try {
                rng = new AESCounterRNG(new DevUrandomSeedGenerator());
            } catch (SeedException se) {
                LoggerFactory.getLogger(UUIDGenerator.class)
                    .warn("Unable to initialize AESCounterRNG - /dev/urandom seed failed", se);
                byte[] seed = new byte[16];
                random.nextBytes(seed);
                rng = new AESCounterRNG(seed);
            }
        } catch (GeneralSecurityException gse) {
            LoggerFactory.getLogger(UUIDGenerator.class).error("Unable to initialize AES cipher for AESCounterRNG",
                gse);
        }
        this.rbg = Generators.randomBasedGenerator(rng);
    }

    public static UUID randomUUID() {
        return INSTANCE.rbg.generate();
    }
}