(VB.NET UWP/WinRT) Verify an XML Signature with Multiple References

Demonstrates how to verify an XML digital signature that contains multiple references.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

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

' An example of an enveloping XML signature with mulitple references is available at
' https://www.chilkatsoft.com/exampleData/envelopedMultipleRefs.xml

' This example will show how to verify the signature and all references, and also how
' to verify each reference individually.  This is useful to distinguish which part
' of the XML signature validation failed.  It could be that one or more of the references
' failed because of a hash computation mismatch.  Or it could be that the signature over
' the SignedInfo failed.  

' First, let's grab the sample XML signature.
Dim http As New Chilkat.Http
Dim sbXml As New Chilkat.StringBuilder
Dim success As Boolean = Await http.QuickGetSbAsync("https://www.chilkatsoft.com/exampleData/envelopedMultipleRefs.xml",sbXml)
If (success <> True) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


' Load the XML containing the signature to be verified.
Dim verifier As New Chilkat.XmlDSig
success = verifier.LoadSignatureSb(sbXml)
If (success <> True) Then
    Debug.WriteLine(verifier.LastErrorText)
    Exit Sub
End If


Dim verifyReferenceDigests As Boolean = True

' The quick way to validate all references and the signature over the SignedInfo
' is to call VerifySignature with verifyReferenceDigests equal to True.
Dim verified As Boolean = verifier.VerifySignature(verifyReferenceDigests)
Debug.WriteLine("Signature and all reference digests verified = " & verified)


' Let's pretend the call to VerifySignature returned False.  Something did not validate.
' Was it one or more of the References that did not hash to the correct value?
' Or was it the signature over the SignedInfo that failed?
' We can check just the signature over the SignedInfo by passing False to VerifySignature.
' This allows us to skip the hashing and checking each Reference.  
verifyReferenceDigests = False
Dim signedInfoVerified As Boolean = verifier.VerifySignature(verifyReferenceDigests)
Debug.WriteLine("Neglecting the reference hashes, the SignedInfo validation result = " & signedInfoVerified)


' We can also verify each reference digest separately
Dim numRefs As Integer = verifier.NumReferences
Dim i As Integer = 0
While i < numRefs
    Dim refDigestVerified As Boolean = verifier.VerifyReferenceDigest(i)
    Debug.WriteLine("Reference " & i & " digest verified = " & refDigestVerified)
    i = i + 1
End While

' For this sample XML signature with 3 References, we get the following output:

' Signature and all reference digests verified = True
' Neglecting the reference hashes, the SignedInfo validation result = True
' Reference 0 digest verified = True
' Reference 1 digest verified = True
' Reference 2 digest verified = Tru