Initial Commit

iTechSharp/srcbc/crypto/prng/ReversedWindowGenerator.cs

@@ -0,0 +1,98 @@
+using System;
+
+namespace Org.BouncyCastle.Crypto.Prng
+{
+	/// <remarks>
+	/// 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>
+	/// </remarks>
+	public class ReversedWindowGenerator
+		: IRandomGenerator
+	{
+		private readonly IRandomGenerator generator;
+
+		private byte[] window;
+		private int windowCount;
+
+		public ReversedWindowGenerator(
+			IRandomGenerator	generator,
+			int					windowSize)
+		{
+			if (generator == null)
+				throw new ArgumentNullException("generator");
+			if (windowSize < 2)
+				throw new ArgumentException("Window size must be at least 2", "windowSize");
+
+			this.generator = generator;
+			this.window = new byte[windowSize];
+		}
+
+		/// <summary>Add more seed material to the generator.</summary>
+		/// <param name="seed">A byte array to be mixed into the generator's state.</param>
+		public virtual void AddSeedMaterial(
+			byte[] seed)
+		{
+			lock (this)
+			{
+				windowCount = 0;
+				generator.AddSeedMaterial(seed);
+			}
+		}
+
+		/// <summary>Add more seed material to the generator.</summary>
+		/// <param name="seed">A long value to be mixed into the generator's state.</param>
+		public virtual void AddSeedMaterial(
+			long seed)
+		{
+			lock (this)
+			{
+				windowCount = 0;
+				generator.AddSeedMaterial(seed);
+			}
+		}
+
+		/// <summary>Fill byte array with random values.</summary>
+		/// <param name="bytes">Array to be filled.</param>
+		public virtual void NextBytes(
+			byte[] bytes)
+		{
+			doNextBytes(bytes, 0, bytes.Length);
+		}
+
+		/// <summary>Fill byte array with random values.</summary>
+		/// <param name="bytes">Array to receive bytes.</param>
+		/// <param name="start">Index to start filling at.</param>
+		/// <param name="len">Length of segment to fill.</param>
+		public virtual void NextBytes(
+			byte[]	bytes,
+			int		start,
+			int		len)
+		{
+			doNextBytes(bytes, start, len);
+		}
+
+		private void doNextBytes(
+			byte[]	bytes,
+			int		start,
+			int		len)
+		{
+			lock (this)
+			{
+				int done = 0;
+				while (done < len)
+				{
+					if (windowCount < 1)
+					{
+						generator.NextBytes(window, 0, window.Length);
+						windowCount = window.Length;
+					}
+
+					bytes[start + done++] = window[--windowCount];
+				}
+			}
+		}
+	}
+}