How to get the Certificate information from clickonce deployment manifest xml file

I'm trying to parse the xml file to get the Certificate info from ClickOnce Manifest. What I need is the X509Certificate information. Example file looks like this:

<?xml version="1.0" encoding="utf-8"?>
<asmv1:assembly xsi:schemaLocation="urn:schemas-microsoft-com:asm.v1 assembly.adaptive.xsd" manifestVersion="1.0" xmlns:asmv1="urn:schemas-microsoft-com:asm.v1" xmlns="urn:schemas-microsoft-com:asm.v2" xmlns:asmv2="urn:schemas-microsoft-com:asm.v2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:co.v1="urn:schemas-microsoft-com:clickonce.v1" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3" xmlns:dsig="http://www.w3.org/2000/09/xmldsig#" xmlns:co.v2="urn:schemas-microsoft-com:clickonce.v2">
  <asmv1:assemblyIdentity name="someName.Xbap.exe" version="2.5.18.1" publicKeyToken="3i3cc7f44s0b9526" language="neutral" processorArchitecture="msil" type="win32" />
  <application />
  <entryPoint>
    <assemblyIdentity name="someName.AFW.Xbap" version="2.5.18.1" language="neutral" processorArchitecture="msil" />
    <commandLine file="someName.AFW.Xbap.exe" parameters="" />
    <hostInBrowser xmlns="urn:schemas-microsoft-com:asm.v3" />
  </entryPoint>
  <publisherIdentity name="CN=HOSTNAME" issuerKeyHash="4534734c4984227c4fa0asdd4eb114524aaed397" />
  <Signature Id="StrongNameSignature" xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo>
      <CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
      <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" />
          <Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
        </Transforms>
        <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
        <DigestValue>MVvHBmUFm2j7PwKjbzig0y7jdBo=</DigestValue>
      </Reference>
    </SignedInfo>
    <SignatureValue>someRandomSignatureValue</SignatureValue>
    <KeyInfo Id="StrongNameKeyInfo">
      <KeyValue>
        <RSAKeyValue>
          <Modulus>someRandomModulusValue</Modulus>
          <Exponent>AQAB</Exponent>
        </RSAKeyValue>
      </KeyValue>
      <msrel:RelData xmlns:msrel="http://schemas.microsoft.com/windows/rel/2005/reldata">
        <r:license xmlns:r="urn:mpeg:mpeg21:2003:01-REL-R-NS" xmlns:as="http://schemas.microsoft.com/windows/pki/2005/Authenticode">
          <r:grant>
            <as:ManifestInformation Hash="manifesthash" Description="" Url="">
              <as:assemblyIdentity name="Somename.Xbap.exe" version="1.0.18.51" publicKeyToken="3b3bc7b44b4b8810" language="neutral" processorArchitecture="msil" type="win32" />
            </as:ManifestInformation>
            <as:SignedBy />
            <as:AuthenticodePublisher>
              <as:X509SubjectName>CN=HostName</as:X509SubjectName>
            </as:AuthenticodePublisher>
          </r:grant>
          <r:issuer>
            <Signature Id="AuthenticodeSignature" xmlns="http://www.w3.org/2000/09/xmldsig#">
              <SignedInfo>
                <CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
                <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" />
                    <Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
                  </Transforms>
                  <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
                  <DigestValue>asdasda+asdaasdasdad=</DigestValue>
                </Reference>
              </SignedInfo>
              <SignatureValue>someRandomSignatureValue==</SignatureValue>
              <KeyInfo>
                <KeyValue>
                  <RSAKeyValue>
                    <Modulus>someRandomSignatureValue</Modulus>
                    <Exponent>AQAB</Exponent>
                  </RSAKeyValue>
                </KeyValue>
                <X509Data>
                  <X509Certificate>!!!this is the required certificate information!!!</X509Certificate>
                </X509Data>
              </KeyInfo>
            </Signature>
          </r:issuer>
        </r:license>
      </msrel:RelData>
    </KeyInfo>
  </Signature>
</asmv1:assembly>

I try to parse it like:

XmlDocument xmlDoc = new XmlDocument();
    xmlDoc.Load(filePath);
    XmlNode securityNode = xmlDoc.SelectSingleNode("/Signature/KeyInfo/msrel:RelData/r:license/r:issuer/Signature/KeyInfo/X509Data/X509Certificate");

When I execute it, I get XPathException

I've also tried one namespace variant.

Solution

These are some steps you missed. First, you need to use XmlNamespaceManager to register prefix-to-namespaceUri mapping :

var nsMapping = new XmlNamespaceManager(xmlDoc.NameTable);
nsMapping.AddNamespace("msrel", "http://schemas.microsoft.com/windows/rel/2005/reldata");
nsMapping.AddNamespace("r", "urn:mpeg:mpeg21:2003:01-REL-R-NS");

Second, besides above 2 namespaces, you also need to register the default namespace (the namespace which declared without prefix) for use in the XPath :

nsMapping.AddNamespace("d", "http://www.w3.org/2000/09/xmldsig#");

Third, pass the namespace manager as second parameter of SelectSingleNode() in addition to using registered prefixes properly in the XPath :

var xpath = "//d:Signature/d:KeyInfo/msrel:RelData/r:license/r:issuer/d:Signature/d:KeyInfo/d:X509Data/d:X509Certificate";
XmlNode securityNode = xmlDoc.SelectSingleNode(xpath, nsMapping);

Missing above particularly step will trigger XPathException as you mentioned in the question. And btw, the following much simpler XPath should also works for this case:

var xpath = "//d:X509Certificate";