package org.bouncycastle.crypto.prng;

import java.security.SecureRandom;

import org.bouncycastle.crypto.prng.drbg.SP80090DRBG;

public class SP800SecureRandom
    extends SecureRandom
{
    private final DRBGProvider drbgProvider;
    private final boolean predictionResistant;
    private final SecureRandom randomSource;
    private final EntropySource entropySource;

    private SP80090DRBG drbg;

    SP800SecureRandom(SecureRandom randomSource, EntropySource entropySource, DRBGProvider drbgProvider, boolean predictionResistant)
    {
        this.randomSource = randomSource;
        this.entropySource = entropySource;
        this.drbgProvider = drbgProvider;
        this.predictionResistant = predictionResistant;
    }

    public void setSeed(byte[] seed)
    {
        synchronized (this)
        {
            if (randomSource != null)
            {
                this.randomSource.setSeed(seed);
            }
        }
    }

    public void setSeed(long seed)
    {
        synchronized (this)
        {
            // this will happen when SecureRandom() is created
            if (randomSource != null)
            {
                this.randomSource.setSeed(seed);
            }
        }
    }

    public void nextBytes(byte[] bytes)
    {
        synchronized (this)
        {
            if (drbg == null)
            {
                drbg = drbgProvider.get(entropySource);
            }

            // check if a reseed is required...
            if (drbg.generate(bytes, null, predictionResistant) < 0)
            {
                drbg.reseed(null);
                drbg.generate(bytes, null, predictionResistant);
            }
        }
    }

    public byte[] generateSeed(int numBytes)
    {
        return EntropyUtil.generateSeed(entropySource, numBytes);
    }

    /**
     * Force a reseed of the DRBG
     *
     * @param additionalInput optional additional input
     */
    public void reseed(byte[] additionalInput)
    {
        drbg.reseed(additionalInput);
    }
}

package org.bouncycastle.crypto.prng;

import java.security.SecureRandom;

import org.bouncycastle.crypto.prng.drbg.SP80090DRBG;

public class SP800SecureRandom
    extends SecureRandom
{
    private final DRBGProvider drbgProvider;
    private final boolean predictionResistant;
    private final SecureRandom randomSource;
    private final EntropySource entropySource;

    private SP80090DRBG drbg;

    SP800SecureRandom(SecureRandom randomSource, EntropySource entropySource, DRBGProvider drbgProvider, boolean predictionResistant)
    {
        this.randomSource = randomSource;
        this.entropySource = entropySource;
        this.drbgProvider = drbgProvider;
        this.predictionResistant = predictionResistant;
    }

    public void setSeed(byte[] seed)
    {
        synchronized (this)
        {
            if (randomSource != null)
            {
                this.randomSource.setSeed(seed);
            }
        }
    }

    public void setSeed(long seed)
    {
        synchronized (this)
        {
            // this will happen when SecureRandom() is created
            if (randomSource != null)
            {
                this.randomSource.setSeed(seed);
            }
        }
    }

    public void nextBytes(byte[] bytes)
    {
        synchronized (this)
        {
            if (drbg == null)
            {
                drbg = drbgProvider.get(entropySource);
            }

            // check if a reseed is required...
            if (drbg.generate(bytes, null, predictionResistant) < 0)
            {
                drbg.reseed(null);
                drbg.generate(bytes, null, predictionResistant);
            }
        }
    }

    public byte[] generateSeed(int numBytes)
    {
        return EntropyUtil.generateSeed(entropySource, numBytes);
    }

    /**
     * Force a reseed of the DRBG
     *
     * @param additionalInput optional additional input
     */
    public void reseed(byte[] additionalInput)
    {
        synchronized (this)
        {
            if (drbg == null)
            {
                drbg = drbgProvider.get(entropySource);
            }

            drbg.reseed(additionalInput);
        }
    }
}

Fix race condition