如何在一定范围内生成密码安全的随机整数? [英] How to generate a cryptographically secure random integer within a range?

问题描述

我必须在给定范围内为生成密码的程序生成一个统一的，安全的随机整数.现在我用这个:

I have to generate a uniform, secure random integer within a given range for a program that generates passwords. Right now I use this :

RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
byte[] rand = new byte[4];
rng.GetBytes(rand);
int i = BitConverter.ToUInt16(rand, 0);
int result = i%max;   //max is the range's upper bound (the lower is 0)

此方法可安全用于加密目的吗?如果没有，我该怎么办?

Is this method safe to use for cryptographic purposes ? If not, how should I do it ?

推荐答案

您可以查看从 https://gist.github.com/1017834 ，这是Stephen Toub和Shawn Farkas的原始版本.在此类中，他们实现了一些随机生成器，这些生成器似乎在密码上是安全的.

You can have a look to CryptoRandom class taken from https://gist.github.com/1017834 which is the Original version by Stephen Toub and Shawn Farkas. In this class they implement several random generators that seem to be cryptographically secures.

我在项目中使用了以下版本进行随机int生成.

I have used the following version in my projects for random int generation.

public class RandomGenerator
{
    readonly RNGCryptoServiceProvider csp;

    public RandomGenerator()
    {
        csp = new RNGCryptoServiceProvider();
    }

    public int Next(int minValue, int maxExclusiveValue)
    {
        if (minValue >= maxExclusiveValue)
            throw new ArgumentOutOfRangeException("minValue must be lower than maxExclusiveValue");

        long diff = (long)maxExclusiveValue - minValue;
        long 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)
    {
        byte[] buffer = new byte[bytesNumber];
        csp.GetBytes(buffer);
        return buffer;
    }
}

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