XmlDsigXPathTransform Class
Assembly: System.Security (in system.security.dll)
The XmlDsigXPathTransform class allows you to address an XML document using the XPath language. This class uses an XPath expression to select the XML nodes you want to sign or encrypt while removing all others from either cryptographic operation.
Use the XmlDsigXPathTransform class to sign or encrypt specific parts of an XML document using an XPath expression. For information on initializing the XmlDsigXPathTransform class to the value of an XPath transform string, see the LoadInnerXml method.
The Uniform Resource Identifier (URI) that describes the XmlDsigXPathTransform class is defined by the XmlDsigXPathTransformUrl field.
For more information about the XPath transform, see Section 6.6.3 of the XMLDSIG specification, which is available from the W3C at www.w3.org/TR/xmldsig-core/.
This section contains two code examples. The first code example shows how to sign and verify an XML document using the XmlDsigXPathTransform class with an envelope signature. This example signs an XML document and saves the signature in a new XML document. The second code example demonstrates how to call members of the XmlDsigXPathTransform class.
Example #1
' ' This example signs an XML file using an ' envelope signature. It then verifies the ' signed XML. ' Imports System Imports System.Security.Cryptography Imports System.Security.Cryptography.X509Certificates Imports System.Security.Cryptography.Xml Imports System.Text Imports System.Xml Module SignVerifyEnvelope Sub Main(ByVal args() As String) ' Generate a signing key. Dim Key As New RSACryptoServiceProvider() Try ' Create an XML file to sign. CreateSomeXml("Example.xml") Console.WriteLine("New XML file created.") ' Sign the XML that was just created and save it in a ' new file. SignXmlFile("Example.xml", "SignedExample.xml", Key, "ancestor-or-self::TempElement") Console.WriteLine("XML file signed.") ' Verify the signature of the signed XML. Console.WriteLine("Verifying signature...") Dim result As Boolean = VerifyXmlFile("SignedExample.xml") ' Display the results of the signature verification to \ ' the console. If result Then Console.WriteLine("The XML signature is valid.") Else Console.WriteLine("The XML signature is not valid.") End If Catch e As CryptographicException Console.WriteLine(e.Message) Finally Key.Clear() End Try End Sub ' Sign an XML file and save the signature in a new file. Sub SignXmlFile(ByVal FileName As String, ByVal SignedFileName As String, ByVal Key As RSA, ByVal XPathString As String) ' Create a new XML document. Dim doc As New XmlDocument() ' Format the document to ignore white spaces. doc.PreserveWhitespace = False ' Load the passed XML file using it's name. doc.Load(New XmlTextReader(FileName)) ' Create a SignedXml object. Dim signedXml As New SignedXml(doc) ' Add the key to the SignedXml document. signedXml.SigningKey = Key ' Create a reference to be signed. Dim reference As New Reference() reference.Uri = "" ' Create an XmlDsigXPathTransform object using ' the helper method 'CreateXPathTransform' defined ' later in this sample. Dim XPathTransform As XmlDsigXPathTransform = CreateXPathTransform(XPathString) ' Add the transform to the reference. reference.AddTransform(XPathTransform) ' Add the reference to the SignedXml object. signedXml.AddReference(reference) ' Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate). Dim keyInfo As New KeyInfo() keyInfo.AddClause(New RSAKeyValue(CType(Key, RSA))) signedXml.KeyInfo = keyInfo ' Compute the signature. signedXml.ComputeSignature() ' Get the XML representation of the signature and save ' it to an XmlElement object. Dim xmlDigitalSignature As XmlElement = signedXml.GetXml() ' Append the element to the XML document. doc.DocumentElement.AppendChild(doc.ImportNode(xmlDigitalSignature, True)) ' Save the signed XML document to a file specified ' using the passed string. Dim xmltw As New XmlTextWriter(SignedFileName, New UTF8Encoding(False)) doc.WriteTo(xmltw) xmltw.Close() End Sub ' Verify the signature of an XML file and return the result. Function VerifyXmlFile(ByVal Name As String) As [Boolean] ' Create a new XML document. Dim xmlDocument As New XmlDocument() ' Format using white spaces. xmlDocument.PreserveWhitespace = True ' Load the passed XML file into the document. xmlDocument.Load(Name) ' Create a new SignedXml object and pass it ' the XML document class. Dim signedXml As New SignedXml(xmlDocument) ' Find the "Signature" node and create a new ' XmlNodeList object. Dim nodeList As XmlNodeList = xmlDocument.GetElementsByTagName("Signature") ' Load the signature node. signedXml.LoadXml(CType(nodeList(0), XmlElement)) ' Check the signature and return the result. Return signedXml.CheckSignature() End Function ' Create the XML that represents the transform. Function CreateXPathTransform(ByVal XPathString As String) As XmlDsigXPathTransform ' Create a new XMLDocument object. Dim doc As New XmlDocument() ' Create a new XmlElement. Dim xPathElem As XmlElement = doc.CreateElement("XPath") ' Set the element text to the value ' of the XPath string. xPathElem.InnerText = XPathString ' Create a new XmlDsigXPathTransform object. Dim xForm As New XmlDsigXPathTransform() ' Load the XPath XML from the element. xForm.LoadInnerXml(xPathElem.SelectNodes(".")) ' Return the XML that represents the transform. Return xForm End Function ' Create example data to sign. Sub CreateSomeXml(ByVal FileName As String) ' Create a new XmlDocument object. Dim document As New XmlDocument() ' Create a new XmlNode object. Dim node As XmlNode = document.CreateNode(XmlNodeType.Element, "", "MyXML", "Don't_Sign") ' Append the node to the document. document.AppendChild(node) ' Create a new XmlNode object. Dim subnode As XmlNode = document.CreateNode(XmlNodeType.Element, "", "TempElement", "Sign") ' Add some text to the node. subnode.InnerText = "Here is some data to sign." ' Append the node to the document. document.DocumentElement.AppendChild(subnode) ' Save the XML document to the file name specified. Dim xmltw As New XmlTextWriter(FileName, New UTF8Encoding(False)) document.WriteTo(xmltw) xmltw.Close() End Sub End Module
Example #2
Imports System Imports System.IO Imports System.Xml Imports System.Security.Cryptography Imports System.Security.Cryptography.Xml Class Class1 <STAThread()> _ Shared Sub Main(ByVal args() As String) ' Encrypt a sample XML string. Dim productsXml As XmlDocument = LoadProducts() ShowTransformProperties(productsXml) ' Encrypt an XPath Xml string. Dim transformXml As XmlDocument = LoadTransformByXml() ShowTransformProperties(transformXml) ' Use XmlDsigXPathTransform to resolve a Uri. Dim baseUri As New Uri("http://www.contoso.com") Dim relativeUri As String = "xml" Dim absoluteUri As Uri = ResolveUris(baseUri, relativeUri) Console.WriteLine("This sample completed successfully; " + "press Enter to exit.") Console.ReadLine() End Sub 'Main ' Encrypt the text in the specified XmlDocument. Private Shared Sub ShowTransformProperties(ByVal xmlDoc As XmlDocument) ' Create a new XMLDocument object. Dim doc As New XmlDocument() ' Create a new XmlElement. Dim xPathElem As XmlElement = doc.CreateElement("XPath") ' Set the element text to the value ' of the XPath string. xPathElem.InnerText = "ancestor-or-self::PRODUCTS" ' Create a new XmlDsigXPathTransform object. Dim xmlTransform As New XmlDsigXPathTransform() ' Load the XPath XML from the element. xmlTransform.LoadInnerXml(xPathElem.SelectNodes(".")) ' Ensure the transform is using the proper algorithm. xmlTransform.Algorithm = SignedXml.XmlDsigXPathTransformUrl ' Retrieve the XML representation of the current transform. Dim xmlInTransform As XmlElement = xmlTransform.GetXml() Console.WriteLine(vbLf + "Xml representation of the current transform: ") Console.WriteLine(xmlInTransform.OuterXml) ' Retrieve the valid input types for the current transform. Dim validInTypes As Type() = xmlTransform.InputTypes ' Verify the xmlTransform can accept the XMLDocument as an ' input type. Dim i As Integer For i = 0 To validInTypes.Length If validInTypes(i).Equals(xmlDoc.GetType()) Then ' Load the document into the transfrom. xmlTransform.LoadInput(xmlDoc) Try ' This transform is created for demonstration purposes. Dim secondTransform As New XmlDsigXPathTransform() Dim classDescription As String = secondTransform.ToString() xmlTransform.LoadInnerXml(xPathElem.SelectNodes(".")) Catch Console.WriteLine("Caught exception while trying to " + "load the specified Xml document. The document " + "requires an XPath element to be valid.") End Try Exit For End If Next i Dim validOutTypes As Type() = xmlTransform.OutputTypes For i = validOutTypes.Length - 1 To 0 Step -1 If validOutTypes(i).Equals(GetType(System.Xml.XmlDocument)) Then Try Dim xmlDocumentType As Type = GetType(System.Xml.XmlDocument) Dim xmlDocumentOutput As XmlDocument = CType(xmlTransform.GetOutput(xmlDocumentType), XmlDocument) ' Display to the console the Xml before and after ' encryption. Console.WriteLine("Result of the GetOutput method call" + " from the current transform: " + xmlDocumentOutput.OuterXml) Catch ex As Exception Console.WriteLine("Unexpected exception caught: " + ex.ToString()) End Try Exit For ElseIf validOutTypes(i).Equals(GetType(System.Xml.XmlNodeList)) Then Try Dim xmlNodeListType As Type = GetType(System.Xml.XmlNodeList) Dim xmlNodes As XmlNodeList = CType(xmlTransform.GetOutput(xmlNodeListType), XmlNodeList) ' Display to the console the Xml before and after ' encryption. Console.WriteLine("Encoding the following message: " + xmlDoc.InnerText) Console.WriteLine("Nodes of the XmlNodeList retrieved " + "from GetOutput:") Dim j As Integer For j = 0 To xmlNodes.Count Console.WriteLine("Node " + j + " has the following name: " + xmlNodes.Item(j).Name + " and the following InnerXml: " + xmlNodes.Item(j).InnerXml) Next j Catch ex As Exception Console.WriteLine("Unexpected exception caught: " + ex.ToString()) End Try Exit For Else Dim outputObject As Object = xmlTransform.GetOutput() End If Next i End Sub 'ShowTransformProperties ' Create an XML document for the dsig namespace. Private Shared Function LoadTransformByXml() As XmlDocument Dim xmlDoc As New XmlDocument() Dim transformXml As String = "<Signature><Reference URI=''><Transforms>" transformXml += "<Transform><XPath " transformXml += "xmlns:dsig='http://www.w3.org/2000/09/xmldsig#'>" transformXml += "not(ancestor-or-self::dsig:Signature)" transformXml += "</XPath></Transform>" transformXml += "</Transforms></Reference></Signature>" xmlDoc.LoadXml(transformXml) Return xmlDoc End Function 'LoadTransformByXml ' Create an XML document describing various products. Private Shared Function LoadProducts() As XmlDocument Dim xmlDoc As New XmlDocument() Dim contosoProducts As String = "<PRODUCTS>" contosoProducts += "<PRODUCT><ID>123</ID>" contosoProducts += "<DESCRIPTION>Router</DESCRIPTION></PRODUCT>" contosoProducts += "<PRODUCT><ID>456</ID>" contosoProducts += "<DESCRIPTION>Keyboard</DESCRIPTION></PRODUCT>" contosoProducts += "<PRODUCT><ID>789</ID>" contosoProducts += "<DESCRIPTION>Monitor</DESCRIPTION></PRODUCT>" contosoProducts += "</PRODUCTS>" xmlDoc.LoadXml(contosoProducts) Return xmlDoc End Function 'LoadProducts ' Resolve the specified base and relative Uri's . Private Shared Function ResolveUris(ByVal baseUri As Uri, ByVal relativeUri As String) As Uri Dim xmlResolver As New XmlUrlResolver() xmlResolver.Credentials = System.Net.CredentialCache.DefaultCredentials Dim xmlTransform As New XmlDsigXPathTransform() xmlTransform.Resolver = xmlResolver Dim absoluteUri As Uri = xmlResolver.ResolveUri(baseUri, relativeUri) If Not (absoluteUri Is Nothing) Then Console.WriteLine(vbLf + "Resolved the base Uri and relative Uri to the following:") Console.WriteLine(absoluteUri.ToString()) Else Console.WriteLine("Unable to resolve the base Uri and relative Uri") End If Return absoluteUri End Function End Class
System.Security.Cryptography.Xml.Transform
System.Security.Cryptography.Xml.XmlDsigXPathTransform
Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.