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XmlDsigEnvelopedSignatureTransform Class

Represents the enveloped signature transform for an XML digital signature as defined by the W3C.

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

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

The XmlDsigEnvelopedSignatureTransform class removes the <Signature> element from an XML document before the digest is computed. With this transform, you can sign and verify all elements of an XML document except the XML digital signature elements.

Although you can create and insert a signature into an XML document, verifying the modified document using the embedded signature will fail because the document now has additional elements. This transform removes the <Signature> element and allows you to verify the document using its original form.

Use the XmlDsigEnvelopedSignatureTransform class whenever you create an enveloped signature.

For more information about the enveloped signature transform, see Section 6.6.4 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 example demonstrates how to sign an XML file using an envelope signature. The second example demonstrates how to use members of the XmlDsigEnvelopedSignatureTransform 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



Public Class SignVerifyEnvelope

   Overloads Public Shared Sub Main(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. 
   Public Shared Sub SignXmlFile(FileName As String, SignedFileName As String, 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

      ' 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. 
   Public Shared Function VerifyXmlFile(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. 
   Public Shared Sub CreateSomeXml(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, "", "MyElement", "samples")

      ' Add some text to the node.
      node.InnerText = "Example text to be signed." 

      ' Append the node to the document.
      document.AppendChild(node)

      ' 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 Class

Example #2

Imports System
Imports System.IO
Imports System.Xml
Imports System.Security.Cryptography
Imports System.Security.Cryptography.Xml
Imports System.Security.Cryptography.X509Certificates

Public Class Form1
    Inherits System.Windows.Forms.Form

    Private certificatePath As String = "..\\my509.cer" 

    ' Event handler for Run button. 
    Private Sub Button1_Click( _
        ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click

        tbxOutput.Cursor = Cursors.WaitCursor
        tbxOutput.Text = "" 

        ' Encrypt an XML message 
        Dim productsXml As XmlDocument = LoadProducts()
        ShowTransformProperties(productsXml)

        SignDocument(productsXml)
        ShowTransformProperties(productsXml)

        ' Use XmlDsigEnvelopedSignatureTransform 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)

        ' Align interface and conclude application.
        WriteLine(vbCrLf + "This sample completed successfully;" + _
            " press Exit to continue.")

        ' Reset the cursor.
        tbxOutput.Cursor = Cursors.Default
    End Sub 

    ' Encrypt the text in the specified XmlDocument. 
    Private Sub ShowTransformProperties(ByVal xmlDoc As XmlDocument)
        Dim xmlTransform As New XmlDsigEnvelopedSignatureTransform

        ' Ensure the transform is using the proper algorithm.
        xmlTransform.Algorithm = _
            SignedXml.XmlDsigEnvelopedSignatureTransformUrl

        ' Retrieve the XML representation of the current transform. 
        Dim xmlInTransform As XmlElement = xmlTransform.GetXml()

        WriteLine(vbCrLf + "Xml representation of the current transform: ")
        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. 
        For i As Int16 = 0 To validInTypes.Length Step 1
            If (validInTypes(i).Equals(xmlDoc.GetType())) Then 
                ' Load the document into the transfrom.
                xmlTransform.LoadInput(xmlDoc)

                Dim IncludeComments As Boolean = True 
                ' This transform is created for demonstration purposes. 
                Dim secondTransform As _
                    New XmlDsigEnvelopedSignatureTransform(IncludeComments)

                Dim classDescription As String = secondTransform.ToString()

                ' This call does not perform as expected. 
                ' An enveloped signature has no inner XML elements
                secondTransform.LoadInnerXml(xmlDoc.SelectNodes("//."))
                Exit For 
            End If 
        Next 

        Dim validOutTypes() As Type = xmlTransform.OutputTypes
        For i As Int16 = validOutTypes.Length - 1 To 0 Step -1
            If (validOutTypes(i).Equals(GetType(System.Xml.XmlDocument))) Then 
                Try 
                    Dim xmlDocumentType As Type
                    xmlDocumentType = GetType(System.Xml.XmlDocument)

                    Dim xmlDocumentOutput As XmlDocument
                    xmlDocumentOutput = CType( _
                        xmlTransform.GetOutput(xmlDocumentType), _
                        XmlDocument)

                    ' Display to the console the Xml before and after 
                    ' encryption.
                    WriteLine("Result of the GetOutput method call from " + _
                        "the current transform: " + _
                        xmlDocumentOutput.OuterXml)
                Catch ex As Exception
                    WriteLine("Unexpected exception caught: " + ex.ToString())

                End Try 
                Exit For 
            ElseIf (validOutTypes(i).Equals( _
                GetType(System.Xml.XmlNodeList))) Then 

                Try 
                    Dim xmlNodeListType As Type
                    xmlNodeListType = GetType(System.Xml.XmlNodeList)
                    Dim xmlNodes As XmlNodeList
                    xmlNodes = CType( _
                        xmlTransform.GetOutput(xmlNodeListType), _
                        System.Xml.XmlNodeList)

                    ' Display to the console the Xml before and after 
                    ' encryption.
                    WriteLine("Encoding the following message: " + _
                        xmlDoc.InnerText)

                    WriteLine("Nodes of the XmlNodeList retrieved from " + _
                        "GetOutput:")

                    For j As Int16 = 0 To xmlNodes.Count - 1 Step 1
                        WriteLine("Node " + j.ToString() + " has the " + _
                            "following name: " + xmlNodes.Item(j).Name + _
                            " and the following InnerXml: " + _
                            xmlNodes.Item(j).InnerXml)
                    Next 
                Catch ex As Exception
                    WriteLine("Unexpected exception caught: " + ex.ToString())
                End Try 

                Exit For 
            Else 
                Dim outputObject As Object = xmlTransform.GetOutput()
            End If 
        Next 
    End Sub 

    Private 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 

    ' Create a signature and add it to the specified document. 
    Private Sub SignDocument(ByRef xmlDoc As XmlDocument)
        ' Generate a signing key. 
        Dim Key As New RSACryptoServiceProvider

        ' Create a SignedXml object. 
        Dim signedXml As New SignedXml(xmlDoc)

        ' Add the key to the SignedXml document. 
        signedXml.SigningKey = Key

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

        ' Add an enveloped transformation to the reference.
        Reference.AddTransform(New XmlDsigEnvelopedSignatureTransform)

        ' Add the reference to the SignedXml object.
        SignedXml.AddReference(Reference)

        Try 
            ' Create a new KeyInfo object. 
            Dim keyInfo As New keyInfo

            ' Load the X509 certificate. 
            Dim MSCert As X509Certificate
            MSCert = X509Certificate.CreateFromCertFile(certificatePath)

            ' Load the certificate into a KeyInfoX509Data object 
            ' and add it to the KeyInfo object.
            keyInfo.AddClause(New KeyInfoX509Data(MSCert))

            ' Add the KeyInfo object to the SignedXml object.
            signedXml.KeyInfo = keyInfo

        Catch ex As FileNotFoundException
            WriteLine("Unable to load the following file: " + certificatePath)

        End Try 
        ' Compute the signature.
        signedXml.ComputeSignature()

        ' Add the signature branch to the original tree so it is enveloped.
        xmlDoc.DocumentElement.AppendChild(signedXml.GetXml())
    End Sub 

    ' Resolve the specified base and relative Uri's . 
    Private 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 XmlDsigEnvelopedSignatureTransform
        xmlTransform.Resolver = xmlResolver

        Dim absoluteUri As Uri = xmlResolver.ResolveUri(baseUri, relativeUri)

        If Not absoluteUri Is Nothing Then
            WriteLine(vbCrLf + "Resolved the base Uri and relative Uri " + _
                "to the following:")
            WriteLine(absoluteUri.ToString())
        Else
            WriteLine("Unable to resolve the base Uri and relative Uri")
        End If 

        Return absoluteUri
    End Function 

    ' Write specified message and carriage return to the output textbox. 
    Private Sub WriteLine(ByVal message As String)
        tbxOutput.AppendText(Message + vbCrLf)

    End Sub 

    ' Event handler for Exit button. 
    Private Sub Button2_Click( _
        ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button2.Click

        Application.Exit()
    End Sub
#Region " Windows Form Designer generated code " 

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call 

    End Sub 

    'Form overrides dispose to clean up the component list. 
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then 
            If Not (components Is Nothing) Then
                components.Dispose()
            End If 
        End If 
        MyBase.Dispose(disposing)
    End Sub 

    'Required by the Windows Form Designer 
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer 
    'It can be modified using the Windows Form Designer.   
    'Do not modify it using the code editor. 
    Friend WithEvents Panel2 As System.Windows.Forms.Panel
    Friend WithEvents Panel1 As System.Windows.Forms.Panel
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Button2 As System.Windows.Forms.Button
    Friend WithEvents tbxOutput As System.Windows.Forms.RichTextBox
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.Panel2 = New System.Windows.Forms.Panel
        Me.Button1 = New System.Windows.Forms.Button
        Me.Button2 = New System.Windows.Forms.Button
        Me.Panel1 = New System.Windows.Forms.Panel
        Me.tbxOutput = New System.Windows.Forms.RichTextBox
        Me.Panel2.SuspendLayout()
        Me.Panel1.SuspendLayout()
        Me.SuspendLayout()
        
        'Panel2 
        
        Me.Panel2.Controls.Add(Me.Button1)
        Me.Panel2.Controls.Add(Me.Button2)
        Me.Panel2.Dock = System.Windows.Forms.DockStyle.Bottom
        Me.Panel2.DockPadding.All = 20
        Me.Panel2.Location = New System.Drawing.Point(0, 320)
        Me.Panel2.Name = "Panel2" 
        Me.Panel2.Size = New System.Drawing.Size(616, 64)
        Me.Panel2.TabIndex = 1
        
        'Button1 
        
        Me.Button1.Dock = System.Windows.Forms.DockStyle.Right
        Me.Button1.Font = New System.Drawing.Font( _
            "Microsoft Sans Serif", _
            9.0!, _
            System.Drawing.FontStyle.Regular, _
            System.Drawing.GraphicsUnit.Point, _
            CType(0, Byte))
        Me.Button1.Location = New System.Drawing.Point(446, 20)
        Me.Button1.Name = "Button1" 
        Me.Button1.Size = New System.Drawing.Size(75, 24)
        Me.Button1.TabIndex = 2
        Me.Button1.Text = "&Run" 
        
        'Button2 
        
        Me.Button2.Dock = System.Windows.Forms.DockStyle.Right
        Me.Button2.Font = New System.Drawing.Font( _
            "Microsoft Sans Serif", _
            9.0!, _
            System.Drawing.FontStyle.Regular, _
            System.Drawing.GraphicsUnit.Point, _
            CType(0, Byte))
        Me.Button2.Location = New System.Drawing.Point(521, 20)
        Me.Button2.Name = "Button2" 
        Me.Button2.Size = New System.Drawing.Size(75, 24)
        Me.Button2.TabIndex = 3
        Me.Button2.Text = "E&xit" 
        
        'Panel1 
        
        Me.Panel1.Controls.Add(Me.tbxOutput)
        Me.Panel1.Dock = System.Windows.Forms.DockStyle.Fill
        Me.Panel1.DockPadding.All = 20
        Me.Panel1.Location = New System.Drawing.Point(0, 0)
        Me.Panel1.Name = "Panel1" 
        Me.Panel1.Size = New System.Drawing.Size(616, 320)
        Me.Panel1.TabIndex = 2
        
        'tbxOutput 
        
        Me.tbxOutput.AccessibleDescription = _
            "Displays output from application." 
        Me.tbxOutput.AccessibleName = "Output textbox." 
        Me.tbxOutput.Dock = System.Windows.Forms.DockStyle.Fill
        Me.tbxOutput.Location = New System.Drawing.Point(20, 20)
        Me.tbxOutput.Name = "tbxOutput" 
        Me.tbxOutput.Size = New System.Drawing.Size(576, 280)
        Me.tbxOutput.TabIndex = 1
        Me.tbxOutput.Text = "Click the Run button to run the application." 
        
        'Form1 
        
        Me.AutoScaleBaseSize = New System.Drawing.Size(6, 15)
        Me.ClientSize = New System.Drawing.Size(616, 384)
        Me.Controls.Add(Me.Panel1)
        Me.Controls.Add(Me.Panel2)
        Me.Name = "Form1" 
        Me.Text = "XmlDsigEnvelopedSignatureTransform" 
        Me.Panel2.ResumeLayout(False)
        Me.Panel1.ResumeLayout(False)
        Me.ResumeLayout(False)

    End Sub

#End Region
End Class 

' This sample produces the following output: 

' Xml representation of the current transform:  
' <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" 
' xmlns="http://www.w3.org/2000/09/xmldsig#" /> 
' Result of the GetOutput method call from the current transform: <PRODUCTS> 
' <PRODUCT><ID>123</ID><DESCRIPTION>Router</DESCRIPTION></PRODUCT><PRODUCT> 
' <ID>456</ID><DESCRIPTION>Keyboard</DESCRIPTION></PRODUCT><PRODUCT><ID>789 
' </ID><DESCRIPTION>Monitor</DESCRIPTION></PRODUCT></PRODUCTS> 
' Unable to load the following file: ..\\my509.cer 
'  
' Xml representation of the current transform:  
' <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" 
'  xmlns="http://www.w3.org/2000/09/xmldsig#" /> 
' Result of the GetOutput method call from the current transform: <PRODUCTS> 
' <PRODUCT><ID>123</ID><DESCRIPTION>Router</DESCRIPTION></PRODUCT><PRODUCT> 
' <ID>456</ID><DESCRIPTION>Keyboard</DESCRIPTION></PRODUCT><PRODUCT><ID>789 
' </ID><DESCRIPTION>Monitor</DESCRIPTION></PRODUCT><Signature xmlns= 
' "http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod  
' Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" /> 
' <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" /> 
' <Reference URI=""><Transforms><Transform Algorithm="http://www.w3.org/2000 
' /09/xmldsig#enveloped-signature" /></Transforms><DigestMethod Algorithm= 
' "http://www.w3.org/2000/09/xmldsig#sha1" /><DigestValue>KvPW6HUiIUMEDS0YSoTg 
' po2JPbA=</DigestValue></Reference></SignedInfo><SignatureValue>c/njCGDru/aWA 
' mWG83I+mWO040xOzxvmNx0b0o8ZyPc9j5VwApdAt103OGBtB1H6EkOvt7Ekw+PVuUo8m5LzLPyaT 
' xUDMbb2kZZ5itSkGD4rmMUMUMuzrkAoquJZjxeOydBJ2CMehV2rE3RMPLIwRX176DZVy5JKU6Cb7 
' PR2Rpw=</SignatureValue></Signature></PRODUCTS> 
'  
' Resolved the base Uri and relative Uri to the following: 
' http://www.contoso.com/xml 
'  
' This sample completed successfully; press Exit to continue.

System.Object
  System.Security.Cryptography.Xml.Transform
    System.Security.Cryptography.Xml.XmlDsigEnvelopedSignatureTransform

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, 1.1, 1.0
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