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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
package org.bouncycastle.crypto.prng;
/**
* Utility methods for making use of EntropySources.
*/
public class EntropyUtil
{
/**
* Generate numBytes worth of entropy from the passed in entropy source.
*
* @param entropySource the entropy source to request the data from.
* @param numBytes the number of bytes of entropy requested.
* @return a byte array populated with the random data.
*/
public static byte[] generateSeed(EntropySource entropySource, int numBytes)
{
byte[] bytes = new byte[numBytes];
if (numBytes * 8 <= entropySource.entropySize())
{
byte[] ent = entropySource.getEntropy();
System.arraycopy(ent, 0, bytes, 0, bytes.length);
}
else
{
int entSize = entropySource.entropySize() / 8;
for (int i = 0; i < bytes.length; i += entSize)
{
byte[] ent = entropySource.getEntropy();
if (ent.length <= bytes.length - i)
{
System.arraycopy(ent, 0, bytes, i, ent.length);
}
else
{
System.arraycopy(ent, 0, bytes, i, bytes.length - i);
}
}
}
return bytes;
}
}