99 lines
2.3 KiB
C#
99 lines
2.3 KiB
C#
using System;
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namespace Org.BouncyCastle.Crypto.Prng
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{
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/// <remarks>
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/// Takes bytes generated by an underling RandomGenerator and reverses the order in
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/// each small window (of configurable size).
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/// <p>
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/// Access to internals is synchronized so a single one of these can be shared.
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/// </p>
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/// </remarks>
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public class ReversedWindowGenerator
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: IRandomGenerator
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{
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private readonly IRandomGenerator generator;
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private byte[] window;
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private int windowCount;
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public ReversedWindowGenerator(
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IRandomGenerator generator,
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int windowSize)
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{
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if (generator == null)
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throw new ArgumentNullException("generator");
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if (windowSize < 2)
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throw new ArgumentException("Window size must be at least 2", "windowSize");
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this.generator = generator;
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this.window = new byte[windowSize];
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}
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/// <summary>Add more seed material to the generator.</summary>
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/// <param name="seed">A byte array to be mixed into the generator's state.</param>
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public virtual void AddSeedMaterial(
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byte[] seed)
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{
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lock (this)
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{
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windowCount = 0;
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generator.AddSeedMaterial(seed);
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}
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}
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/// <summary>Add more seed material to the generator.</summary>
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/// <param name="seed">A long value to be mixed into the generator's state.</param>
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public virtual void AddSeedMaterial(
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long seed)
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{
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lock (this)
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{
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windowCount = 0;
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generator.AddSeedMaterial(seed);
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}
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}
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/// <summary>Fill byte array with random values.</summary>
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/// <param name="bytes">Array to be filled.</param>
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public virtual void NextBytes(
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byte[] bytes)
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{
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doNextBytes(bytes, 0, bytes.Length);
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}
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/// <summary>Fill byte array with random values.</summary>
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/// <param name="bytes">Array to receive bytes.</param>
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/// <param name="start">Index to start filling at.</param>
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/// <param name="len">Length of segment to fill.</param>
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public virtual void NextBytes(
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byte[] bytes,
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int start,
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int len)
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{
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doNextBytes(bytes, start, len);
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}
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private void doNextBytes(
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byte[] bytes,
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int start,
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int len)
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{
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lock (this)
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{
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int done = 0;
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while (done < len)
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{
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if (windowCount < 1)
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{
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generator.NextBytes(window, 0, window.Length);
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windowCount = window.Length;
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}
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bytes[start + done++] = window[--windowCount];
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}
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}
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}
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}
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}
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