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The Long Term Stable (LTS) Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains the JCA/JCE provider and low-level API for the BC LTS version 2.73.7 for Java 8 and later.
package org.bouncycastle.crypto;
import java.security.SecureRandom;
import org.bouncycastle.crypto.prng.EntropySource;
import org.bouncycastle.crypto.prng.EntropySourceProvider;
class IncrementalEntropySourceProvider
implements EntropySourceProvider
{
private final SecureRandom random;
private final boolean predictionResistant;
/**
* Create a entropy source provider based on the passed in SecureRandom.
*
* @param random the SecureRandom to base EntropySource construction on.
* @param isPredictionResistant boolean indicating if the SecureRandom is based on prediction resistant entropy or not (true if it is).
*/
public IncrementalEntropySourceProvider(SecureRandom random, boolean isPredictionResistant)
{
this.random = random;
this.predictionResistant = isPredictionResistant;
}
/**
* Return an entropy source that will create bitsRequired bits of entropy on
* each invocation of getEntropy().
*
* @param bitsRequired size (in bits) of entropy to be created by the provided source.
* @return an EntropySource that generates bitsRequired bits of entropy on each call to its getEntropy() method.
*/
public EntropySource get(final int bitsRequired)
{
return new IncrementalEntropySource()
{
final int numBytes = (bitsRequired + 7) / 8;
public boolean isPredictionResistant()
{
return predictionResistant;
}
public byte[] getEntropy()
{
try
{
return getEntropy(0);
}
catch (InterruptedException e)
{
Thread.currentThread().interrupt();
throw new IllegalStateException("initial entropy fetch interrupted"); // should never happen
}
}
public byte[] getEntropy(long pause)
throws InterruptedException
{
byte[] seed = new byte[numBytes];
for (int i = 0; i < numBytes / 8; i++)
{
// we need to be mindful that we may not be the only thread/process looking for entropy
sleep(pause);
byte[] rn = random.generateSeed(8);
System.arraycopy(rn, 0, seed, i * 8, rn.length);
}
int extra = numBytes - ((numBytes / 8) * 8);
if (extra != 0)
{
sleep(pause);
byte[] rn = random.generateSeed(extra);
System.arraycopy(rn, 0, seed, seed.length - rn.length, rn.length);
}
return seed;
}
public int entropySize()
{
return bitsRequired;
}
};
}
private static void sleep(long ms)
throws InterruptedException
{
if (ms != 0)
{
Thread.sleep(ms);
}
}
}
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