如何使用RNGCryptoServiceProvider获取大于256的随机数？

Question

如何使用RNGCryptoServiceProvider获得大于256的随机数？

码:

private static RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

byte[] randomNumber = new byte[1];

//Fill the array with a random value.   

rngCsp.GetBytes(randomNumber);

Answer 1

填充1到8个字节的数组,并使用BitConverter提取整数.

    static ulong RandomUInt64()
    {
        var rng = new RNGCryptoServiceProvider();
        var bytes = new byte[8];
        rng.GetBytes(bytes);
        return BitConverter.ToUInt64(bytes);
    }

如果要生成特定范围内的随机数并且还想保留分布,则应生成一系列数字并丢弃不在预期范围内的值(蒙特卡罗方法).我怀疑如果你正在考虑一个安全的加密随机数生成器,这就是你想要的行为.

    static int Random(RandomNumberGenerator rng, int min, int max)
    {
        if (min > max) throw new ArgumentException(nameof(min));
        if (min == max) return min;

        var bytes = new byte[4];

        long diff = max - min;

        while (true)
        {
            rng.GetBytes(bytes);

            var rand = BitConverter.ToUInt32(bytes);
            var remainder = (1 + (long) uint.MaxValue) % diff;

            if (rand < max - remainder)
            {
                return (int) (min + (rand % diff));
            }
        }
    }

调用提供程序时会产生很大的开销,因此请考虑缓冲对GetBytes的调用.要更快地生成数字,您还可以从随机缓冲区中选择最多日志(范围)/ log(2)位,此外还要丢弃超出范围的样本(以保留分布).

public class RandomGenerator
{
    private readonly RandomNumberGenerator _rng;

    public RandomGenerator(RandomNumberGenerator rng)
    {
        _rng = rng;
    }

    public IEnumerable<int> Next(ulong range)
    {
        var buffer = new byte[8 * 512];
        var bits = (int) Math.Ceiling(Math.Log(range) / Math.Log(2));
        var mask = (ulong) ~(~0 << bits);

        while (true)
        {
            _rng.GetBytes(buffer);

            for (var i = 0; i < buffer.Length / 8; i += 8)
            {
                var num = BitConverter.ToUInt64(buffer, i);
                var n = num & mask;

                if (n <= range - 1)
                {
                    yield return (int) n;
                }
            }
        }
    }

    public IEnumerable<int> Next(int min, int max)
    {
        if (min > max) throw new ArgumentOutOfRangeException(nameof(min));
        var range = (ulong) Math.Abs(max - min);
        return Next(range).Select(r => r + min);
    }
}

这将为您提供有用的API:

  var rng = new RNGCryptoServiceProvider();
  var random = new RandomGenerator(rng);
  var randomValues = random.Next(-1000, 1000).Take(100).ToArray();