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SignedXml Class

Provides a wrapper on a core XML signature object to facilitate creating XML signatures.

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

'Declaration
Public Class SignedXml
'Usage
Dim instance As SignedXml

The SignedXml class is the main class used for XML signing and verification (XMLDSIG) in the .NET Framework. XMLDSIG is a standards-based, interoperable way to sign and verify all or part of an XML document or other data that is addressable from a Uniform Resource Identifier (URI). The .NET Framework XMLDSIG classes implement the World Wide Web Consortium (W3C) specification for XML signing and verification located at http://www.w3.org/TR/xmldsig-core/.

Use the SignedXml class whenever you need to share signed XML data between applications or organizations in a standard way. Any data signed using this class can be verified by any conforming implementation of the W3C specification for XMLDSIG.

XMLDSIG creates a <Signature> element, which contains a digital signature of an XML document or other data that is addressable from a URI. The <Signature> element can optionally contain information about where to find a key that will verify the signature and which cryptographic algorithm was used for signing.

The SignedXml class allows you to create the following three kinds of XML digital signatures:

Signature Type

Description

Enveloped signature

The signature is contained within the XML document being signed.

Enveloping signature

The signed XML is contained within the <Signature> element.

Detached signature

The signature is in a separate document from the data being signed.

Use one of the following methods to exchange key information:

  • Do not include any key information. If you choose this option, both parties must agree on an algorithm and key before they exchange a digital signature.

  • Include a public key in the <EncryptedKey> element.

  • Include the location of the key in the URI attribute of the <RetrievalMethod> element. Both parties must agree on the key location ahead of time and this location must be kept secret.

  • Include a string name that maps to a key in the <KeyName> element. Both parties must agree on the key name mapping before they exchange encrypted data and this mapping must be kept secret.

The following code example shows how to sign and verify an entire XML document using an enveloped 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



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", Key)

         ' 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. This method does not   
   ' save the public key within the XML file.  This file cannot be verified unless   
   ' the verifying code has the key with which it was signed. 
   Public Shared Sub SignXmlFile(FileName As String, SignedFileName As String, Key As RSA)
      ' Create a new XML document. 
      Dim doc As New XmlDocument()

      ' Load the passed XML file using its 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)

      ' 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 against an asymetric  
   ' algorithm and return the result. 
   Public Shared Function VerifyXmlFile(Name As [String], Key As RSA) As [Boolean]
      ' Create a new XML document. 
      Dim xmlDocument As New XmlDocument()

      ' 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(Key)
   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

The following code example shows how to sign and verify an object that is addressable from a Uniform Resource Identifier, using a detached signature.


' This example signs a file specified by a URI  
' using a detached signature. It then verifies   
' the signed XML. 

Imports System
Imports System.Security.Cryptography
Imports System.Security.Cryptography.Xml
Imports System.Text
Imports System.Xml




Class XMLDSIGDetached


   <STAThread()>  _
   Overloads Shared Sub Main(args() As String)
      ' The URI to sign. 
      Dim resourceToSign As String = "http://www.microsoft.com" 

      ' The name of the file to which to save the XML signature. 
      Dim XmlFileName As String = "xmldsig.xml" 

      Try 

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

         Console.WriteLine("Signing: {0}", resourceToSign)

         ' Sign the detached resourceand save the signature in an XML file.
         SignDetachedResource(resourceToSign, XmlFileName, Key)

         Console.WriteLine("XML Signature was succesfully computed and saved to {0}.", XmlFileName)

         ' Verify the signature of the signed XML.
         Console.WriteLine("Verifying signature...")

         'Verify the XML signature in the XML file against the key. 
         Dim result As Boolean = VerifyDetachedSignature(XmlFileName, Key)

         ' 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. This method does not   
   ' save the public key within the XML file.  This file cannot be verified unless   
   ' the verifying code has the key with which it was signed. 
   Public Shared Sub SignDetachedResource(URIString As String, XmlSigFileName As String, Key As RSA)
      ' Create a SignedXml object. 
      Dim signedXml As New SignedXml()

      ' Assign the key to the SignedXml object.
      signedXml.SigningKey = Key

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

      ' Add the passed URI to the reference object.
      reference.Uri = URIString

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

      ' 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()

      ' Save the signed XML document to a file specified 
      ' using the passed string. 
      Dim xmltw As New XmlTextWriter(XmlSigFileName, New UTF8Encoding(False))
      xmlDigitalSignature.WriteTo(xmltw)
      xmltw.Close()
   End Sub  


   ' Verify the signature of an XML file against an asymetric  
   ' algorithm and return the result. 
   Public Shared Function VerifyDetachedSignature(XmlSigFileName As String, Key As RSA) As [Boolean]
      ' Create a new XML document. 
      Dim xmlDocument As New XmlDocument()

      ' Load the passedXML file into the document.
      xmlDocument.Load(XmlSigFileName)

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

      ' 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 against the passed asymetric key 
      ' and return the result. 
      Return signedXml.CheckSignature(Key)
   End Function  
End Class

The following code example shows how to sign and verify a single element of an XML document using an enveloping 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.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 
            ' Specify an element to sign.  
            Dim elements As String() = New String() {"#tag1"}

            ' Sign an XML file and save the signature to a  
            ' new file.
            SignXmlFile("Test.xml", "SignedExample.xml", Key, elements)
            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 
            ' Clear resources associated with the  
            ' RSACryptoServiceProvider.
            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 ElementsToSign() As String)
        ' Check the arguments.   
        If FileName Is Nothing Then 
            Throw New ArgumentNullException("FileName")
        End If 
        If SignedFileName Is Nothing Then 
            Throw New ArgumentNullException("SignedFileName")
        End If 
        If Key Is Nothing Then 
            Throw New ArgumentNullException("Key")
        End If 
        If ElementsToSign Is Nothing Then 
            Throw New ArgumentNullException("ElementsToSign")
        End If 
        ' 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

        ' Loop through each passed element to sign  
        ' and create a reference. 
        Dim s As String 
        For Each s In ElementsToSign
            ' Create a reference to be signed. 
            Dim reference As New Reference()
            reference.Uri = s

            ' 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)
        Next s

        ' 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]
        ' Check the arguments.   
        If Name Is Nothing Then 
            Throw New ArgumentNullException("Name")
        End If 
        ' 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 
End Module

System.Object
  System.Security.Cryptography.Xml.SignedXml

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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