Add a better random number generator

Geekbot.net/Lib/RandomNumberGenerator/IRandomNumberGenerator.cs

@@ -0,0 +1,7 @@
+namespace Geekbot.net.Lib.RandomNumberGenerator
+{
+    public interface IRandomNumberGenerator
+    {
+        int Next(int minValue, int maxExclusiveValue);
+    }
+}

Geekbot.net/Lib/RandomNumberGenerator/RandomNumberGenerator.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Security.Cryptography;
+
+namespace Geekbot.net.Lib.RandomNumberGenerator
+{
+    public class RandomNumberGenerator : IRandomNumberGenerator
+    {
+        readonly RNGCryptoServiceProvider csp;
+
+        public RandomNumberGenerator()
+        {
+            csp = new RNGCryptoServiceProvider();
+        }
+
+        public int Next(int minValue, int maxExclusiveValue)
+        {
+            if (minValue >= maxExclusiveValue)
+            {
+                throw new ArgumentOutOfRangeException("minValue must be lower than maxExclusiveValue");
+            }
+
+            var diff = (long)maxExclusiveValue - minValue;
+            var upperBound = uint.MaxValue / diff * diff;
+
+            uint ui;
+            do
+            {
+                ui = GetRandomUInt();
+            } while (ui >= upperBound);
+            return (int)(minValue + (ui % diff));
+        }
+
+        private uint GetRandomUInt()
+        {
+            var randomBytes = GenerateRandomBytes(sizeof(uint));
+            return BitConverter.ToUInt32(randomBytes, 0);
+        }
+
+        private byte[] GenerateRandomBytes(int bytesNumber)
+        {
+            var buffer = new byte[bytesNumber];
+            csp.GetBytes(buffer);
+            return buffer;
+        }
+    }
+}