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package org.bouncycastle.crypto.prng;
/**
* Takes bytes generated by an underling RandomGenerator and reverses the order in
* each small window (of configurable size).
* <p>
* Access to internals is synchronized so a single one of these can be shared.
* </p>
*/
public class ReversedWindowGenerator
implements RandomGenerator
{
private final RandomGenerator generator;
private byte[] window;
private int windowCount;
public ReversedWindowGenerator(
RandomGenerator generator,
int windowSize)
{
if (generator == null)
{
throw new IllegalArgumentException("generator cannot be null");
}
if (windowSize < 2)
{
throw new IllegalArgumentException("windowSize must be at least 2");
}
this.generator = generator;
this.window = new byte[windowSize];
}
/**
* Add more seed material to the generator.
*
* @param seed a byte array to be mixed into the generator's state.
*/
public void addSeedMaterial(
byte[] seed)
{
synchronized (this)
{
windowCount = 0;
generator.addSeedMaterial(seed);
}
}
/**
* Add more seed material to the generator.
*
* @param seed a long value to be mixed into the generator's state.
*/
public void addSeedMaterial(
long seed)
{
synchronized (this)
{
windowCount = 0;
generator.addSeedMaterial(seed);
}
}
/**
* Fill bytes with random values.
*
* @param bytes byte array to be filled.
*/
public void nextBytes(
byte[] bytes)
{
doNextBytes(bytes, 0, bytes.length);
}
/**
* Fill part of bytes with random values.
*
* @param bytes byte array to be filled.
* @param start index to start filling at.
* @param len length of segment to fill.
*/
public void nextBytes(
byte[] bytes,
int start,
int len)
{
doNextBytes(bytes, start, len);
}
private void doNextBytes(
byte[] bytes,
int start,
int len)
{
synchronized (this)
{
int done = 0;
while (done < len)
{
if (windowCount < 1)
{
generator.nextBytes(window, 0, window.length);
windowCount = window.length;
}
bytes[start + done++] = window[--windowCount];
}
}
}
}
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