FIPS validated application with HMAC function based on SHA512?

Question

I'm building a FIPS validated application and have the FIPS mode turned on on my computer. I need an HMAC function hopefully based on SHA512. I understand that the HMAC SHA1 function is FIPS validated but I have a hash function SHA512CryptoServiceProvider which is FIPS validated and I know that FIPS does in fact allow for SHA512. Is there a similar HMAC function in C# that does FIPS validated HMAC SHA512?

Catarrhine

Answer 1

There is a HMACSHA512 Class, but it uses the SHA512Managed Class internally, which is not FIPS certified.

You could try to create your own HMACSHA512 Class based on the SHA512CryptoServiceProvider Class:

public class MyHMACSHA512 : HMAC
{
    public MyHMACSHA512(byte[] key)
    {
        HashName = "System.Security.Cryptography.SHA512CryptoServiceProvider";
        HashSizeValue = 512;
        BlockSizeValue = 128;
        Key = key;
    }
}

Mainspring

Yah thats true the only problem with it is that with FIPS compatibility turned on it doesn't work. I need an HMAC SHA512 that is FIPS compatible. For instance, SHA512Cng breaks in FIPS compatibility mode, SHA512CryptoServiceProvider does not. HMACSHA512 breaks in FIPS compatibility mode HMACSHA1 does not. I would like to find an HMAC based on SHA512 that does not break FIPS compatibility. – Catarrhine

I see. The HMACSHA512 class internally uses the SHA512Managed class by default, which is not FIPS validated. You could try to create your own HMACSHA512 class based on the SHA512CryptoServiceProvider class. – Mainspring

Thanks for the response. I tried that method but I got exceptions. It looks like SHA512CryptoServiceProvider isn't a valid hash name msdn.microsoft.com/en-us/library/kczffhwa.aspx – Catarrhine

It seems you have to specify the class name including its namespace. msdn.microsoft.com/en-us/library/wet69s13.aspx – Mainspring

When we do this, we side-step the FIPS compatibility error, but is it truly FIPS-compatible? – Languorous

HashName should be AssemblyQualifiedName. It would be better to write like this: HashName = typeof(SHA256CryptoServiceProvider).AssemblyQualifiedName; – Cheriecherilyn

Answer 2

The following worked for me - I was able to create both an AES and SHA256 FIPS happy HMAC:

    /// <summary>Computes a Hash-based Message Authentication Code (HMAC) using the AES hash function.</summary>
    public class AesHmac : HMAC
    {
        /// <summary>Initializes a new instance of the AesHmac class with the specified key data.</summary>
        /// <param name="key">The secret key for AesHmac encryption.</param>
        public AesHmac(byte[] key)
        {
            HashName = "System.Security.Cryptography.AesCryptoServiceProvider";
            HashSizeValue = 128;
            BlockSizeValue = 128;
            Initialize();
            Key = (byte[])key.Clone();
        }
    }

    /// <summary>Computes a Hash-based Message Authentication Code (HMAC) using the SHA256 hash function.</summary>
    public class ShaHmac : HMAC
    {
        /// <summary>Initializes a new instance of the ShaHmac class with the specified key data.</summary>
        /// <param name="key">The secret key for ShaHmac encryption.</param>
        public ShaHmac(byte[] key)
        {
            HashName = "System.Security.Cryptography.SHA256CryptoServiceProvider";
            HashSizeValue = 256;
            BlockSizeValue = 128;
            Initialize();
            Key = (byte[])key.Clone();
        }
    }

Thanks, Ritchie

Beckiebeckley