How to verify digital XML signature

Question

I want to verify that the document was not be modified in any way.

From a Java web service, I receive the following Soap response with a digital XML signature:

<?xml version="1.0" encoding="UTF-8"?><Envelope xmlns="http://schemas.xmlsoap.org/soap/envelope/"><SOAP-ENV:Header xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">  
<wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" SOAP-ENV:mustUnderstand="1">
<wsse:BinarySecurityToken xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" EncodingType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary" ValueType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3" wsu:Id="CertId-38670273">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</wsse:BinarySecurityToken><ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<ds:SignedInfo>
<ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
<ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<ds:Reference URI="#id-32516734">
<ds:Transforms>
<ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
</ds:Transforms>
<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue>Rx5L4j8kF5RVYnC+spUCdvhh5N0=</ds:DigestValue>
</ds:Reference>
<ds:Reference URI="#id-7716709">
<ds:Transforms>
<ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
</ds:Transforms>
<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue>fFr2j5DoKTgpEvX1Se7gTC55bWM=</ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
<ds:SignatureValue>
jG1BaGgNbbk9JCc3R6JsJKY56p++f0+8RM2aL6TGOXS34NAGv48Sp3iAHEAuUt9+JV6w3VDAcFct
no3nCEISa0P4dVWTlPQJue3GVTWnnlcXao95tjukh9o8lIU7vZGgYHBUZLU+jgS6ZcaUlNW4KFUl
AdrPxR5DmJcFyGEtRY2yclqYhnJdnUc+ZBu5eWbRZgbJzR4MgtGsEQcgtftFe2i0CvRbOSe4mt3T
JQzbGY81ssFCnB44vitgjhVLfPd/08amSa5Xn8KRptbNatp2uq1iGXAifJLVup8T0yS0RzaqhCJg
CaHRPFVKFN3WaJcqPZex75KBwSZMZaaJDZW7lQ==
</ds:SignatureValue>
<ds:KeyInfo Id="KeyId-16708261">
<wsse:SecurityTokenReference xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" wsu:Id="STRId-32258670"><wsse:Reference URI="#CertId-38670273" ValueType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3"/></wsse:SecurityTokenReference>
</ds:KeyInfo>
</ds:Signature>
<wsu:Timestamp xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" wsu:Id="id-32516734"><wsu:Created>2017-03-31T09:04:40.352Z</wsu:Created><wsu:Expires>2017-03-31T09:09:40.352Z</wsu:Expires></wsu:Timestamp></wsse:Security><wsa:MessageID xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" SOAP-ENV:mustUnderstand="0">uuid:12b93a00-15f1-11e7-af6b-f16d80f418ae</wsa:MessageID><wsa:To xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" SOAP-ENV:mustUnderstand="0">http://schemas.xmlsoap.org/ws/2004/08/addressing/role/anonymous</wsa:To></SOAP-ENV:Header>


<SOAP-ENV:Body xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" wsu:Id="id-7716709">
...
 </SOAP-ENV:Body></Envelope>

I've found an usefull example to verify the xml file on MSDN:

  ' 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", "http://www.w3.org/2000/09/xmldsig#")

    ' Load the signature node.
    signedXml.LoadXml(CType(nodeList(0), XmlElement))

    ' Check the signature and return the result.
    Return signedXml.CheckSignature()

End Function

Unfortunately, the verification always returns false. I struggle to understand why it doesn't work.

---

UPDATE 1 according to the proposals from Henk Holterman and Simon Mourier:

 Function VerifyXmlFile(ByVal Name As String) As Boolean

    ' <SOAP-ENV:Envelope ... > ... </SOAP-ENV:Envelope>
    Dim xDoc = XDocument.Load(Name)

    ' <wsse:binarySecurityToken ... > ... </wsse:binarySecurityToken>
    Dim xBinarySecurityToken = xDoc.Root.Descendants().Skip(2).FirstOrDefault

    ' <SOAP-ENV:Body ... > ... </SOAP-ENV:Body>
    Dim xBody = xDoc.Root.Elements().Skip(1).FirstOrDefault
    Dim signedXml = New SignedXml(ToXmlElement(xBody))

    Dim xmlDocument As New XmlDocument()
    xmlDocument.PreserveWhitespace = True
    xmlDocument.Load(Name)

    Dim nodeList = xmlDocument.GetElementsByTagName("Signature", "http://www.w3.org/2000/09/xmldsig#")
    signedXml.LoadXml(CType(nodeList(0), XmlElement))

    Dim byteCert = Encoding.UTF8.GetBytes(xBinarySecurityToken.Value)
    Dim cert = New X509Certificates.X509Certificate2(byteCert)

    Return signedXml.CheckSignature(cert, True)

End Function

Public Shared Function ToXmlElement(xElement As XElement) As XmlElement
    Dim xmlDoc = New XmlDocument() With {.PreserveWhitespace = True}
    xmlDoc.Load(xElement.CreateReader())
    Return xmlDoc.DocumentElement
End Function

Resulted in a CryptographicException with the message "Malformed reference element" by calling the function CheckSignature().

---

UPDATE 2 and SOLUTION according to the proposals from @SimonMourier and @lax1089

Private Function VerifyXmlfile(Name As String) As Boolean
    CryptoConfig.AddAlgorithm(GetType(MyXmlDsigC14NTransform), "http://www.w3.org/TR/2001/REC-xml-c14n-20010315")

    Dim xmlDocument As New XmlDocument()
    xmlDocument.PreserveWhitespace = True
    xmlDocument.Load(Name)
    MyXmlDsigC14NTransform.document = xmlDocument

    Dim soapBody As XmlElement = xmlDocument.GetElementsByTagName("SOAP-ENV:Body")(0)
    Dim securityToken = xmlDocument.GetElementsByTagName("SOAP-ENV:Header")(0).FirstChild.NextSibling.FirstChild.NextSibling.InnerText

    Dim signedXml = New SignedXmlWithId(soapBody)

    Dim nodeList = xmlDocument.GetElementsByTagName("Signature", "http://www.w3.org/2000/09/xmldsig#")
    signedXml.LoadXml(CType(nodeList(0), XmlElement))

    Dim byteCert = Convert.FromBase64String(securityToken)
    Dim cert = New X509Certificates.X509Certificate2(byteCert)

    Return signedXml.CheckSignature(cert, True)

End Function

A helper class stolen from Dog Ears

Public Class SignedXmlWithId
Inherits SignedXml

Public Sub New(xml As XmlDocument)
    MyBase.New(xml)
End Sub

Public Sub New(xmlElement As XmlElement)
    MyBase.New(xmlElement)
End Sub

Public Overrides Function GetIdElement(doc As XmlDocument, id As String) As XmlElement
    ' check to see if it's a standard ID reference
    Dim idElem As XmlElement = MyBase.GetIdElement(doc, id)

    If idElem Is Nothing Then
        Dim nsManager As New XmlNamespaceManager(doc.NameTable)
        nsManager.AddNamespace("wsu", "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd")

        idElem = TryCast(doc.SelectSingleNode((Convert.ToString("//*[@wsu:Id=""") & id) + """]", nsManager), XmlElement)
    End If

    Return idElem
End Function

End Class

Credits to @SimonMourier and @CarlosLopez-MSFT

Answer 1

Actually this is a known and documented issue:

The Canonicalization implementation between .NET 3.5 and .NET 4.0 has changed.

I don't know if this works on all XML signatures, but it works from the testing that I've done.

Add the following C14N Transform class to your project:

public class MyXmlDsigC14NTransform: XmlDsigC14NTransform {
  static XmlDocument _document;
  public static XmlDocument document {
    set {
      _document = value;
    }
  }

  public MyXmlDsigC14NTransform() {}

  public override Object GetOutput() {
    return base.GetOutput();
  }

  public override void LoadInnerXml(XmlNodeList nodeList) {
    base.LoadInnerXml(nodeList);
  }

  protected override XmlNodeList GetInnerXml() {
    XmlNodeList nodeList = base.GetInnerXml();
    return nodeList;
  }

  public XmlElement GetXml() {
    return base.GetXml();
  }

  public override void LoadInput(Object obj) {
    int n;
    bool fDefaultNS = true;

    XmlElement element = ((XmlDocument) obj).DocumentElement;

    if (element.Name.Contains("SignedInfo")) {
      XmlNodeList DigestValue = element.GetElementsByTagName("DigestValue", element.NamespaceURI);
      string strHash = DigestValue[0].InnerText;
      XmlNodeList nodeList = _document.GetElementsByTagName(element.Name);

      for (n = 0; n < nodeList.Count; n++) {
        XmlNodeList DigestValue2 = ((XmlElement) nodeList[n]).GetElementsByTagName("DigestValue", ((XmlElement) nodeList[n]).NamespaceURI);
        string strHash2 = DigestValue2[0].InnerText;
        if (strHash == strHash2) break;
      }

      XmlNode node = nodeList[n];

      while (node.ParentNode != null) {
        XmlAttributeCollection attrColl = node.ParentNode.Attributes;
        if (attrColl != null) {
          for (n = 0; n < attrColl.Count; n++) {
            XmlAttribute attr = attrColl[n];
            if (attr.Prefix == "xmlns") {
              element.SetAttribute(attr.Name, attr.Value);
            } else if (attr.Name == "xmlns") {
              if (fDefaultNS) {
                element.SetAttribute(attr.Name, attr.Value);
                fDefaultNS = false;
              }
            }
          }
        }

        node = node.ParentNode;
      }
    }

    base.LoadInput(obj);
  }
}

And register the class using the CryptoConfig.AddAlgorithm method as demonstrated below:

CryptoConfig.AddAlgorithm(typeof(MyXmlDsigC14NTransform), "http://www.w3.org/TR/2001/REC-xml-c14n-20010315"); 

var message = new XmlDocument();
message.PreserveWhitespace = true;
message.Load("XmlSig.xml");

MyXmlDsigC14NTransform.document = message; // The transform class needs the xml document

// Validate signature as normal.  

This should allow you to properly verify an XML signature and resolve your issue.