C# SignatureDescription for SHA256

Question

I am working on a c# signing application. At one point, a System.Security.Cryptography.SignatureDescription needs to be obtained. Does anyone know why description1 below contains a valid structure, while description2 is null? Changing from .Net3.5 to .Net4.5.1 did not help.

SignatureDescription description1 = CryptoConfig.CreateFromName("http://www.w3.org/2000/09/xmldsig#rsa-sha1") as SignatureDescription; SignatureDescription description2 = CryptoConfig.CreateFromName("http://www.w3.org/2001/04/xmldsig-more#rsa-sha256") as SignatureDescription;

It didn't work for SHA512 either. URIs obtained from here.

Create from name doesn't mean you need to enter a URL. Why should changing to .NET 4.5.1 yield another result (if that was true, .NET was very badly backwards compatible). — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jul 15, 2014 at 11:08
re .Net, I figured, however sometimes it doesn't harm to try. Regarding CreateFromName(), I tried using the URI because that works for SHA1. If there are any similar methods to create a SignatureDescription given a particular hashing algorithm, that would be fine. — user2707674
– user2707674, Commented Jul 15, 2014 at 11:43
Btw, one could pass "SHA1" or "SHA256" to CreateFromName(), however the SignatureDescription is not available then for either algorithms. So it seems the full URI is required to get the SignatureDescription. — user2707674
– user2707674, Commented Jul 15, 2014 at 12:35
I am now specifying the signature description strings myself. Once again, this is working for SHA1 but not for SHA256. Any thoughts? SignatureDescription desc = new SignatureDescription(); desc.DeformatterAlgorithm = "System.Security.Cryptography.RSAPKCS1SignatureDeformatter"; desc.DigestAlgorithm = "System.Security.Cryptography.SHA256CryptoServiceProvider"; desc.FormatterAlgorithm = "System.Security.Cryptography.RSAPKCS1SignatureFormatter"; desc.KeyAlgorithm = "System.Security.Cryptography.RSACryptoServiceProvider"; HashAlgorithm hash = desc.CreateDigest(); — user2707674
– user2707674, Commented Jul 23, 2014 at 13:53

user2707674 · Accepted Answer · 2014-07-28 11:38:55Z

1

Apparently RSA-SHA256 is not supported in .Net 3.5. However there's a workaround which can be found here: http://social.msdn.microsoft.com/Forums/vstudio/en-US/6438011b-92fb-4123-a22f-ad071efddf85/xml-digital-signature-with-sha256-algorithm

answered Jul 28, 2014 at 11:38

user2707674

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Cleptus Over a year ago

The workaround it says there is kinda odd. It calls CryptoConfig.AddAlgorithm which is not implemented in 3.5 but in 4.0... If you stick to 3.5 and follow that workaround you should consider Codeplex CryptoConfig2 otherwise it is unlikely you would get it working.

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