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XmlDsigExcC14NTransform Class

Represents the exclusive C14N XML canonicalization transform for a digital signature as defined by the World Wide Web Consortium (W3C), without comments.

Namespace:  System.Security.Cryptography.Xml
Assembly:  System.Security (in System.Security.dll)

'Declaration
Public Class XmlDsigExcC14NTransform _
	Inherits Transform
'Usage
Dim instance As XmlDsigExcC14NTransform

The XmlDsigExcC14NTransform class represents the exclusive C14N XML canonicalization transform without comments. This class is similar to the XmlDsigC14NTransform class, which allows a signer to create a digest using the canonical form of an XML document. However, the XmlDsigExcC14NTransform class excludes ancestor context from a canonicalized subdocument.

Use the XmlDsigC14NTransform class when you need to canonicalize an XML subdocument so that it is independent from its XML context. For example, applications such as Web services that use signed XML within complex communication protocols often need to canonicalize XML in this manner. Such applications often envelop XML within various dynamically constructed elements, which can substantially change the document and cause XML signature verification to fail. The XmlDsigExcC14NTransform class solves this problem by excluding such ancestor context from the canonical subdocument.

Typically, you do not create a new instance of a canonicalization transform class. To specify a canonicalization transform, pass the Uniform Resource Identifier (URI) that describes a transform to the CanonicalizationMethod property, which is accessible from the SignedInfo property. To acquire a reference to the canonicalization transform, use the CanonicalizationMethodObject property, which is accessible from the SignedInfo property.

You are required to create a new instance of a canonicalization transform class only when you want to manually hash an XML document or use your own canonicalization algorithm.

The URI that describes the XmlDsigExcC14NWithCommentsTransform class is defined by the XmlDsigExcC14NWithCommentsTransformUrl field.

The URI that describes the XmlDsigExcC14NTransform class is defined by the XmlDsigExcC14NTransformUrl field.

For more information about the exclusive C14N transform, see the XMLDSIG specification, which is available from the World Wide Web Consortium (W3C) at www.w3.org/TR/xmldsig-core/. The canonicalization algorithm is defined in the W3C Canonical XML specification, which is available at www.w3.org/2001/10/xml-exc-c14n.

The following code example shows how to sign an XML document with the XmlDsigExcC14NTransform class using an envelope signature.


' 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)
        Try 
            ' Generate a signing key. 
            Dim Key As New RSACryptoServiceProvider()

            ' 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)
            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)
        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)
        ' 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

        ' Specify a canonicalization method.
        signedXml.SignedInfo.CanonicalizationMethod = signedXml.XmlDsigExcC14NTransformUrl

        ' Set the InclusiveNamespacesPrefixList property.  
        Dim canMethod As XmlDsigExcC14NTransform = CType(signedXml.SignedInfo.CanonicalizationMethodObject, XmlDsigExcC14NTransform)
        canMethod.InclusiveNamespacesPrefixList = "Sign" 

        ' Create a reference to be signed. 
        Dim reference As New Reference()
        reference.Uri = "" 

        ' Add an enveloped transformation to the reference. 
        Dim env As New XmlDsigEnvelopedSignatureTransform()
        reference.AddTransform(env)

        ' 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))


        If TypeOf doc.FirstChild Is XmlDeclaration Then
            doc.RemoveChild(doc.FirstChild)
        End If 

        ' 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 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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0
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