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package org.spongycastle.crypto.prng;
import org.spongycastle.crypto.Digest;
/**
* Random generation based on the digest with counter. Calling addSeedMaterial will
* always increase the entropy of the hash.
* <p>
* Internal access to the digest is synchronized so a single one of these can be shared.
* </p>
*/
public class DigestRandomGenerator
implements RandomGenerator
{
private static long CYCLE_COUNT = 10;
private long stateCounter;
private long seedCounter;
private Digest digest;
private byte[] state;
private byte[] seed;
// public constructors
public DigestRandomGenerator(
Digest digest)
{
this.digest = digest;
this.seed = new byte[digest.getDigestSize()];
this.seedCounter = 1;
this.state = new byte[digest.getDigestSize()];
this.stateCounter = 1;
}
public void addSeedMaterial(byte[] inSeed)
{
synchronized (this)
{
digestUpdate(inSeed);
digestUpdate(seed);
digestDoFinal(seed);
}
}
public void addSeedMaterial(long rSeed)
{
synchronized (this)
{
digestAddCounter(rSeed);
digestUpdate(seed);
digestDoFinal(seed);
}
}
public void nextBytes(byte[] bytes)
{
nextBytes(bytes, 0, bytes.length);
}
public void nextBytes(byte[] bytes, int start, int len)
{
synchronized (this)
{
int stateOff = 0;
generateState();
int end = start + len;
for (int i = start; i != end; i++)
{
if (stateOff == state.length)
{
generateState();
stateOff = 0;
}
bytes[i] = state[stateOff++];
}
}
}
private void cycleSeed()
{
digestUpdate(seed);
digestAddCounter(seedCounter++);
digestDoFinal(seed);
}
private void generateState()
{
digestAddCounter(stateCounter++);
digestUpdate(state);
digestUpdate(seed);
digestDoFinal(state);
if ((stateCounter % CYCLE_COUNT) == 0)
{
cycleSeed();
}
}
private void digestAddCounter(long seed)
{
for (int i = 0; i != 8; i++)
{
digest.update((byte)seed);
seed >>>= 8;
}
}
private void digestUpdate(byte[] inSeed)
{
digest.update(inSeed, 0, inSeed.length);
}
private void digestDoFinal(byte[] result)
{
digest.doFinal(result, 0);
}
}
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