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using System;
using Org.BouncyCastle.Crypto.Digests;
namespace Org.BouncyCastle.Crypto.Prng
{
/**
* 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
: IRandomGenerator
{
private const long CYCLE_COUNT = 10;
private long stateCounter;
private long seedCounter;
private IDigest digest;
private byte[] state;
private byte[] seed;
public DigestRandomGenerator(
IDigest 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)
{
lock (this)
{
DigestUpdate(inSeed);
DigestUpdate(seed);
DigestDoFinal(seed);
}
}
public void AddSeedMaterial(
long rSeed)
{
lock (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)
{
lock (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 seedVal)
{
ulong seed = (ulong)seedVal;
for (int i = 0; i != 8; i++)
{
digest.Update((byte)seed);
seed >>= 8;
}
}
private void DigestUpdate(byte[] inSeed)
{
digest.BlockUpdate(inSeed, 0, inSeed.Length);
}
private void DigestDoFinal(byte[] result)
{
digest.DoFinal(result, 0);
}
}
}
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