B4X

Verify XML Signature with External Data Reference

See more XML Digital Signatures Examples

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.

B4X

Dim success As Boolean = False

'  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 ChilkatHttp
http.Initialize("http")
Dim sbXml As ChilkatStringBuilder
sbXml.Initialize
success = http.QuickGetSb(url, sbXml)
If success <> True Then
    Log(http.LastErrorText)
    Return
End If


Dim verifier As ChilkatXmlDSig
verifier.Initialize

'  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
    Log(verifier.LastErrorText)
    Return
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
    Log("No reference URI found.")
    Return
End If


'  Download the JPG data to be verified.
Dim jpgData As ChilkatBinData
jpgData.Initialize
success = http.QuickGetBd(refUri, jpgData)
If success <> True Then
    Log(http.LastErrorText)
    Return
End If


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

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