Create a cryptographically secure random GUID in .NET

Question

I want to create a cryptographically secure GUID (v4) in .NET.

.NET's Guid.NewGuid() function is not cryptographically secure, but .NET does provide the System.Security.Cryptography.RNGCryptoServiceProvider class.

I would like to be able to pass a random number function as a delegate to Guid.NewGuid (or even pass some class that provides a generator interface) but it doesn't look as though that is possible with the default implementation.

Can I create a cryptographically secure GUID by using System.GUID and System.Security.Cryptography.RNGCryptoServiceProvider together?

Answer 1

Yes you can, Guid allows you to create a Guid using a byte array, and RNGCryptoServiceProvider can generate a random byte array, so you can use the output to feed a new Guid:

public Guid CreateCryptographicallySecureGuid() 
{
    using (var provider = new RNGCryptoServiceProvider()) 
    {
        var bytes = new byte[16];
        provider.GetBytes(bytes);

        return new Guid(bytes);
    }
}