CryptographicException: Could not create hash algorithm object

Marc George 171 Reputation points

Since upgrading/migrating from .NET 4.3.1 to 6.0 and targeting a Windows Server 7 app service on Azure, I have been encountering the above error when making a call to System.Security.Cryptography.Xml.SignedXml.ComputeSignature(). The cryptography assemblies are now v6.0.0.0.

Remote debugging, I think it is the related to the results of the call to SHA256.Create() which is the DigestAlgorithm parameter in the call. It doesn't have the same content pattern as the others. The parameter values being passed are:

KeyAlgorithm: *"System.Security.Cryptography.RSACryptoServiceProvider, System.Security.Cryptography.Csp, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"*

DigestAlgorithm: *"System.Security.Cryptography.SHA256+Implementation"*

FormatterAlgorithm: *"System.Security.Cryptography.RSAPKCS1SignatureFormatter, System.Security.Cryptography.Algorithms, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"*

DeformatterAlgorithm: *"System.Security.Cryptography.RSAPKCS1SignatureDeformatter, System.Security.Cryptography.Algorithms, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"*

What should the expected value of the DigestAlgorithm be? Something similar to the others?

There have been other reports of issues with the function with the upgrade to 6. Anyone else? Solutions?

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