"An internal error ocurred" when using SHA-2 algorithms with SignedCMS

Hi all,

The other day a customer of mine got this exception when trying to use SHA-2 algorithms with SignedCms class in their .NET 3.5 application:

Exception type: System.Security.Cryptography.CryptographicException
Message: An internal error occurred.

They got the exception on Windows Vista SP2/Server 2008 SP2 and later versions when using using a third-party CSP. Why?

SignedCMS class uses CAPI2 (CryptMsg* API) behind the scenes. CAPI2 requires a CNG provider for any algorithm that is not on this list:

CryptFindOIDInfo Function
Hash Algorithms:


Algorithms that are not listed are supported by using Cryptography API: Next Generation (CNG) only;

In customer's scenario, third-party CSP was a legacy CSP and not a CNG provider.

Summing up, if you want to work with i.e. SHA256, SHA384 & SHA512 algorithms, you will need a CNG provider.

Now, I will post about this in greater detail soon, but SignedCMS class doesn't support CNG. So basically, we cannot use SHA-2 algorithms with that class under this scenario.

I hope this helps.

Alex (Alejandro Campos Magencio)