Cryptographically-strong random number generator in C#.

CryptoRandom.cs

// Cryptographically-strong random number generator 
// Source: MSDN Magazine > 2007 > September > .NET Matters: Tales from the CryptoRandom
// Source URL: http://msdn.microsoft.com/en-us/magazine/cc163367.aspx
// Authors: Stephen Toub & Shawn Farkas

public class CryptoRandom : Random
{
    private RNGCryptoServiceProvider cryptoProvider = new RNGCryptoServiceProvider();
    private byte[] uint32Buffer = new byte[4];

    /// <summary>
    /// An implementation of System.Random used for cryptographically-strong random number generation.
    /// </summary>
    public CryptoRandom() { }

    /// <summary>
    /// An implementation of System.Random used for cryptographically-strong random number generation.
    /// </summary>
    public CryptoRandom(Int32 seedIgnored) { }

    /// <summary>
    /// Returns a nonnegative random number.
    /// </summary>
    /// <returns>
    /// A 32-bit signed integer greater than or equal to zero and less than <see cref="F:System.Int32.MaxValue"/>.
    /// </returns>
    public override Int32 Next()
    {
        cryptoProvider.GetBytes(uint32Buffer);
        return BitConverter.ToInt32(uint32Buffer, 0) & 0x7FFFFFFF;
    }

    /// <summary>
    /// Returns a nonnegative random number less than the specified maximum.
    /// </summary>
    /// <returns>
    /// A 32-bit signed integer greater than or equal to zero, and less than <paramref name="maxValue"/>; that is, the range of return values ordinarily includes zero but not <paramref name="maxValue"/>. However, if <paramref name="maxValue"/> equals zero, <paramref name="maxValue"/> is returned.
    /// </returns>
    /// <param name="maxValue">The exclusive upper bound of the random number to be generated. <paramref name="maxValue"/> must be greater than or equal to zero.</param>
    /// <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="maxValue"/> is less than zero.</exception>
    public override Int32 Next(Int32 maxValue)
    {
        if (maxValue < 0) throw new ArgumentOutOfRangeException("maxValue");
        return Next(0, maxValue);
    }

    /// <summary>
    /// Returns a random number within a specified range.
    /// </summary>
    /// <returns>
    /// A 32-bit signed integer greater than or equal to <paramref name="minValue"/> and less than <paramref name="maxValue"/>; that is, the range of return values includes <paramref name="minValue"/> but not <paramref name="maxValue"/>. If <paramref name="minValue"/> equals <paramref name="maxValue"/>, <paramref name="minValue"/> is returned.
    /// </returns>
    /// <param name="minValue">The inclusive lower bound of the random number returned.</param>
    /// <param name="maxValue">The exclusive upper bound of the random number returned. <paramref name="maxValue"/> must be greater than or equal to <paramref name="minValue"/>.</param>
    /// <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="minValue"/> is greater than <paramref name="maxValue"/>.</exception>
    public override Int32 Next(Int32 minValue, Int32 maxValue)
    {
        if (minValue > maxValue) throw new ArgumentOutOfRangeException("minValue");
        if (minValue == maxValue) return minValue;
        Int64 diff = maxValue - minValue;

        while (true)
        {
            cryptoProvider.GetBytes(uint32Buffer);
            UInt32 rand = BitConverter.ToUInt32(uint32Buffer, 0);

            Int64 max = (1 + (Int64)UInt32.MaxValue);
            Int64 remainder = max % diff;
            if (rand < max - remainder)
            {
                return (Int32)(minValue + (rand % diff));
            }
        }
    }

    /// <summary>
    /// Returns a random number between 0.0 and 1.0.
    /// </summary>
    /// <returns>
    /// A double-precision floating point number greater than or equal to 0.0, and less than 1.0.
    /// </returns>
    public override double NextDouble()
    {
        cryptoProvider.GetBytes(uint32Buffer);
        UInt32 rand = BitConverter.ToUInt32(uint32Buffer, 0);
        return rand / (1.0 + UInt32.MaxValue);
    }

    /// <summary>
    /// Fills the elements of a specified array of bytes with random numbers.
    /// </summary>
    /// <param name="buffer">An array of bytes to contain random numbers.</param>
    /// <exception cref="T:System.ArgumentNullException"><paramref name="buffer"/> is null.
    public override void NextBytes(byte[] buffer)
    {
        if (buffer == null) throw new ArgumentNullException("buffer");
        cryptoProvider.GetBytes(buffer);
    }
}