When will C# AES algorithm be FIPS compliant?

Question

Right now the only way I can get the RijndaelManaged algorithm to work on a computer with the Local Security Setting for FIPS turned on, is to disable it. It is a government computer, so I'm not sure how that will fly. I've seen posts on the msdn blog sites that say they are working on an AES FIPS compliant version, but I cant seem to find out anything more. Does anyone know when this might happen?

Answer 1

I never realized this before this question, but you're right. The constructor has this:

public RijndaelManaged()
{
    if (Utils.FipsAlgorithmPolicy == 1)
    {
        throw new InvalidOperationException(Environment.GetResourceString("Cryptography_NonCompliantFIPSAlgorithm"));
    }
}

System.Security.Cryptography.AesManaged has something similar:

public AesManaged()
{
    if (CoreCryptoConfig.EnforceFipsAlgorithms)
    {
        throw new InvalidOperationException(SR.GetString("Cryptography_NonCompliantFIPSAlgorithm"));
    }
    this.m_rijndael = new RijndaelManaged();
    this.m_rijndael.BlockSize = this.BlockSize;
    this.m_rijndael.KeySize = this.KeySize;
}

Have you tried System.Security.Cryptography.AesCryptoServiceProvider? It should work since it's using the CAPI based FIPS AES implementation built into Windows.

This question on Microsoft's .NET Base Class Library forum discusses which algorithms are FIPS compliant and has good links.

It appears that Microsoft is making a consistent effort to obey the setting of HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Lsa\FIPSAlgorithmPolicy on pre-Vista machines and use of the BCryptGetFipsAlgorithmMode API for post-Vista.

I assume there is non-trivial effort involved in certifying an implementation as FIPS compliant, that is why Microsoft probably doesn't want to repeat the process and only offers the AesCryptoServiceProvider for customers that absolutely need this requirement.

This MSDN blog post has a comment that makes it clearer:

The easy way to figure out if an algorithm is compliant or not is to look at the suffix. None of the *Managed types are FIPS certified. The *CryptoServiceProvider and *Cng types however, may well be FIPS certified. If they implement an algorithm that FIPS allows, and are using the default Microsoft providers, then they will be.

For instance, SHA256Managed is not (because it is *Managed). SHA256CryptoServiceProvider and SHA256Cng are.
MD5CryptoServiceProvider is not (because MD5 is not a FIPS algorithm).

Answer 2

The unmanaged AesCryptoServiceProvider is certified if the OS itself is certified as it calls the OS. And it will be a darned site quicker as well, at the cost of cross platform compatibility.

Answer 3

My site had to get a waver for FIPS compliance in .net.