(VB.NET) Verify XML Signature with External Data Reference

Demonstrates how to verify an XML digital signature where the data is external. In this case, the data is a JPG file.

This example requires Chilkat v9.5.0.69 or greater.

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

' The XML containing the Signature to be verified contains the following:
' <?xml version="1.0" encoding="UTF-8" standalone="no"?>
' <abc>
'   <xyz>
'     <jpg>
'         <name>starfish.jpg</name>
'         <url>https://www.chilkatsoft.com/images/starfish.jpg</url>
'     <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/2001/04/xmldsig-more#rsa-sha256"/><ds:Reference 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:SignedInfo><ds:SignatureValue>MbHOti6nOh9DJP/u7u1+a1u0wRYIGEdaAVk5ehxqeBhcR4qvGvCQ7wLxcfDuwFG2grSg43ANxDYngLqZTeFb5nCfywcuNBQI8FrNRVY5hkyv6kDW1BVN8ot9qPYX9oHxJp1e+nMszIiSxqHX3XDI7YnvFt/0CyeO5JaQQEzXzIwqqb8iUNcH/bJzR6CrTf1hGuQ5MPorG0bRwbYPPHHzipUqHBinK8VbHobnxL7GQHAhR8k9gDD35kZcMxf/74U7pGO19ZzTbdJW5S7q4bVVxvsuU3itTbhHI60pOE14ibrjZtIrPZLVUD3TQqIIF04TChW2NXdYOo3+ij4ZnP8x+g==</ds:SignatureValue><ds:KeyInfo><ds:KeyValue><ds:RSAKeyValue><ds:Modulus>sXeRhM55P13FbpNcXAMR3olbw2Wa6keZIHu5YTZYUBTlYWId+pNiwUz3zFIEo+0IfYR0H27ybIycQO+1IIzJofUFNMAL3tZps2OKPlsjuCPls6kXpXhv/gvhux8LrCtp4PcKWqJ6QVOZKChc7WAx40qFWzHi57ueqRTv3x0kESqGg/VjsqyTEvb55psJO2RsfhLT7+YVh3hImRM3RDaJdkTkPuOxeFyT6N7VXD09329sLuS3QkUbE9zEKDnz9X3d8dEQdJhSI9ba5fxl8R7fu8pB67ElfzFml96X1jLFtzy1pzOT5Fc4ROcaqlYckVzdBq9sxezm6MYmDBjNAcibRw==</ds:Modulus><ds:Exponent>AQAB</ds:Exponent></ds:RSAKeyValue></ds:KeyValue></ds:KeyInfo></ds:Signature></jpg>
'   </xyz>
' </abc>

' The above XML is available at https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml
' First fetch the XML..

Dim url As String = "https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml"
Dim http As New Chilkat.Http
Dim sbXml As New Chilkat.StringBuilder
Dim success As Boolean = http.QuickGetSb(url,sbXml)
If (success <> True) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


Dim verifier As New Chilkat.XmlDSig

' Load the XML containing the signatures to be verified.
' Note that this particular Signature already contains the RSA public key that will be used
' for verification.
success = verifier.LoadSignatureSb(sbXml)
If (success <> True) Then
    Debug.WriteLine(verifier.LastErrorText)
    Exit Sub
End If


' Get the Reference URI, which in this case is the URL to the binary data that was hashed.
' This fetchs the URI attribute value from:  <ds:Reference URI="https://www.chilkatsoft.com/images/starfish.jpg">
Dim refUri As String = verifier.ReferenceUri(0)
If (verifier.LastMethodSuccess <> True) Then
    Debug.WriteLine("No reference URI found.")
    Exit Sub
End If


' Download the JPG data to be verified.
Dim jpgData As New Chilkat.BinData
success = http.QuickGetBd(refUri,jpgData)
If (success <> True) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


' Provide the JPG data to the verifier
verifier.SetRefDataBd(0,jpgData)

' Verify the signature
Dim bVerified As Boolean = verifier.VerifySignature(True)
Debug.WriteLine("Signature verified = " & bVerified)