XML Signature element is not declared

Question

I created XSD using Visual StudioXML Tools. And I use following C# code to validate XML and facing this error.

Error

The elem

Answer 1

If you don't want to change anything to xsd or xml - do the following:

1. (optional) Download xsd from w3 site and save to local disk. W3 site is VERY slow because a lot of software worldwide constantly request those schemas. If you will use that xsd directly - you will often fail by timeout. Some validation tools already have such schemas cached locally, but not .NET validator.

2. Modify your validation method from UPDATE 2 the following way:

   public static bool IsValidXml1(string xmlFilePath, string xsdFilePath, string namespaceName)
   {
       XDocument xdoc = null;
       var settings = new XmlReaderSettings();
       settings.DtdProcessing = DtdProcessing.Ignore;
   
       try
       {
           using (XmlReader xr = XmlReader.Create(xmlFilePath, settings))
           {
               xdoc = XDocument.Load(xr);
               var schemas = new XmlSchemaSet();                    
               schemas.Add(namespaceName, xsdFilePath);                   
               using (var fs = File.OpenRead(@"D:\Temp\xmldsig-core-schema.xsd")) 
               using (var reader = XmlReader.Create(fs, new XmlReaderSettings() {
                   DtdProcessing = DtdProcessing.Ignore // important
               })) {
                   schemas.Add(@"http://www.w3.org/2000/09/xmldsig#", reader);
               }
   
               xdoc.Validate(schemas, null);
   
               return true;
           }
       }
       catch (XmlSchemaValidationException ex)
       {
           // throw;
       }
   
       return false;
   }
   

You have to add that schema using XmlReader and not directly, because if you add directly (like in your update 2) - it will fail to parse DTD block, because when you add XmlSchema to XmlSchemaSet using url (or file path) - it will read that file using XmlReaderSettings with DtdProcessing = DtdProcessing.Prohibit. We need to change that to DtdProcessing.Ignore or DtdProcessing.Parse. After that your validation method will work fine for target xsd and xml file, without any changes (and will correctly fail in case xml does not match xsd).