C# 产生真随机数（RNGCryptoServiceProv

```csharp
public static string Generate(string dictionary, int length)
{
    string result = "";

RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();

byte[] data = new byte[8];
    int max = dictionary.Length - 1;
    for (int i = 0; i < length; i++)
    {
        rng.GetBytes(data);
        int rnd = (int)Math.Round(Math.Abs(BitConverter.ToInt64(data, 0)) / (decimal)long.MaxValue * max, 0);

result += dictionary.Substring(rnd, 1);
    }

return result;
}
```

RNGCryptoServiceProvider

命名空间:   System.Security.Cryptography

程序集:  mscorlib（位于 mscorlib.dll）

微软有自带产生密码的（System.Web.Security.Membership.GeneratePassword），当然也是用到了随机数，它是怎样的呢？其源代码如下：

```csharp
// System.Web.Security.Membership
public static string GeneratePassword(int length, int numberOfNonAlphanumericCharacters)
{
    if (length < 1 || length > 128)
    {
        throw new ArgumentException(SR.GetString("Membership_password_length_incorrect"));
    }
    if (numberOfNonAlphanumericCharacters > length || numberOfNonAlphanumericCharacters < 0)
    {
        throw new ArgumentException(SR.GetString("Membership_min_required_non_alphanumeric_characters_incorrect", new obje-ct[]
        {
            "numberOfNonAlphanumericCharacters"
        }));
    }
    string text;
    int num4;
    do
    {
        byte[] array = new byte[length];
        char[] array2 = new char[length];
        int num = 0;
        new RNGCryptoServiceProvider().GetBytes(array);
        for (int i = 0; i < length; i++)
        {
            int num2 = (int)(array[i] % 87);
            if (num2 < 10)
            {
                array2[i] = (char)(48 + num2);
            }
            else
            {
                if (num2 < 36)
                {
                    array2[i] = (char)(65 + num2 - 10);
                }
                else
                {
                    if (num2 < 62)
                    {
                        array2[i] = (char)(97 + num2 - 36);
                    }
                    else
                    {
                        array2[i] = Membership.punctuations[num2 - 62];
                        num++;
                    }
                }
            }
        }
        if (num < numberOfNonAlphanumericCharacters)
        {
            Random random = new Random();
            for (int j = 0; j < numberOfNonAlphanumericCharacters - num; j++)
            {
                int num3;
                do
                {
                    num3 = random.Next(0, length);
                }
                while (!char.IsLetterOrDigit(array2[num3]));
                array2[num3] = Membership.punctuations[random.Next(0, Membership.punctuations.Length)];
            }
        }
        text = new string(array2);
    }
    while (CrossSitescri-ptingValidation.IsDangerousString(text, out num4));
    return text;
}
```

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