(PowerShell) Verify XML Signature with External URL References

Demonstrates how to verify an XML digital signature that includes references to URLs where the data to be digested is on a web server.

Chilkat .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# The signed XML we wish to verify contains external references such as this:

#     <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref0" URI="https://www.chilkatsoft.com/images/starfish.jpg">
#       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
#       <ds:DigestValue>AOU810yJV5Np/DnO29qpObqiTSTTCDvxGsX5ayiTYXI=</ds:DigestValue>
#     </ds:Reference>
#     <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref1" URI="https://www.chilkatsoft.com/hamlet.xml">
#       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
#       <ds:DigestValue>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</ds:DigestValue>
#     </ds:Reference>

$verifier = New-Object Chilkat.XmlDSig
$http = New-Object Chilkat.Http

# First load the signed XML
$sbSignedXml = New-Object Chilkat.StringBuilder
$success = $sbSignedXml.LoadFile("qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml","utf-8")
if ($success -eq $false) {
    $("Failed to load signed XML.")
    exit
}

$success = $verifier.LoadSignatureSb($sbSignedXml)
if ($success -eq $false) {
    $($verifier.LastErrorText)
    exit
}

# Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
$sbRefUri = New-Object Chilkat.StringBuilder
$bd = New-Object Chilkat.BinData
$numRefs = $verifier.NumReferences
$i = 0
while ($i -lt $numRefs) {
    if ($verifier.IsReferenceExternal($i) -eq $true) {
        $sbRefUri.Clear()
        $sbRefUri.Append($verifier.ReferenceUri($i))
        if ($sbRefUri.StartsWith("https://",$false) -eq $true) {
            $("External URL Reference: " + $sbRefUri.GetAsString())

            # Download the data at the URL and provide to the verifier.
            $success = $http.DownloadBd($sbRefUri.GetAsString(),$bd)
            if ($success -eq $false) {
                $($http.LastErrorText)
                exit
            }

            $success = $verifier.SetRefDataBd($i,$bd)
            if ($success -eq $false) {
                $($verifier.LastErrorText)
                exit
            }

        }

    }

    $i = $i + 1
}

# Now that we have the external data, verify the signature..
$bVerified = $verifier.VerifySignature($true)
if ($bVerified -eq $false) {
    $($verifier.LastErrorText)
}

$("Signature verified = " + $bVerified)