How can I generate a cryptographically secure pseudorandom number in C#?

Is there any fast implementation of cryptographically secure pseudorandom number generator (CSPRNG) for C# 3.0 (.NET Framework 3.5), for authentication tokens?

Solution 1:

using System.Security.Cryptography;
...
using(RandomNumberGenerator rng = new RNGCryptoServiceProvider())
{
    byte[] tokenData = new byte[32];
    rng.GetBytes(tokenData);

    string token = Convert.ToBase64String(tokenData);
}

Solution 2:

That depends on what you mean by fast...

There is no really fast secure random generator. If you want fast, you should use the regular Random class. If you want secure you should use the random generator in the Cryptography namespace, but that is significantly slower. You simply can't have both.

Solution 3:

Upd 2022 in .Net 6 RNGCryptoServiceProvider() is obsolete, usage of static methods of RandomNumberGenerator is recommended

private string GetRandomlyGenerateBase64String(int count)
{
    return Convert.ToBase64String(RandomNumberGenerator.GetBytes(count));
}