(Excel) Create XML Signature with External XML Reference

Demonstrates how to create an XML digital signature where the referenced data is external. In this case, the data is an XML file located at the following URL: https://www.chilkatsoft.com/data/helloWorld.xml

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

' This example inserts an XML signature in the following XML:

' <?xml version="1.0" encoding="UTF-8" standalone="no"?>
' <abc>
'   <xyz>
' 	<name>helloWorld.xml</name>
' 	<url>https://www.chilkatsoft.com/data/helloWorld.xml</url>
'   </xyz>
' </abc>

' Build the above XML to be signed.
Dim xml As Chilkat.Xml
Set xml = Chilkat.NewXml
xml.Tag = "abc"
xml.UpdateChildContent "xyz|name","helloWorld.xml"
xml.UpdateChildContent "xyz|url","https://www.chilkatsoft.com/data/helloWorld.xml"

Dim cert As Chilkat.Cert
Set cert = Chilkat.NewCert


success = cert.LoadPfxFile("qa_data/pfx/test_secret.pfx","secret")
If (success = False) Then
    Debug.Print cert.LastErrorText
    Exit Sub
End If

Dim gen As Chilkat.XmlDSigGen
Set gen = Chilkat.NewXmlDSigGen

' Indicate the location within the XML the Signature will be inserted.
gen.SigLocation = "abc|xyz"

' Get the content of the XML data to be referenced.
Dim http As Chilkat.Http
Set http = Chilkat.NewHttp
Dim sbExternalXml As Chilkat.StringBuilder
Set sbExternalXml = Chilkat.NewStringBuilder
success = http.QuickGetSb("https://www.chilkatsoft.com/data/helloWorld.xml",sbExternalXml)
If (success = False) Then
    Debug.Print http.LastErrorText
    Exit Sub
End If

success = gen.AddExternalXmlRef("https://www.chilkatsoft.com/data/helloWorld.xml",sbExternalXml,"sha256","EXCL_C14N","")
If (success = False) Then
    Debug.Print gen.LastErrorText
    Exit Sub
End If

' Provide the private key for signing via the certificate, and indicate that
' we want the base64 of the certificate embedded in the KeyInfo.
gen.KeyInfoType = "X509Data"
gen.X509Type = "Certificate"


bUsePrivateKey = True
success = gen.SetX509Cert(cert,bUsePrivateKey)
If (success <> True) Then
    Debug.Print gen.LastErrorText
    Exit Sub
End If

' Indicate we want an indented signature for readability.
' This can be removed after debugging is finished..
gen.Behaviors = "IndentedSignature"

' Now create and insert the Signature
Dim sbXml As Chilkat.StringBuilder
Set sbXml = Chilkat.NewStringBuilder
Dim success As Boolean
success = xml.GetXmlSb(sbXml)
success = gen.CreateXmlDSigSb(sbXml)
If (success <> True) Then
    Debug.Print gen.LastErrorText
    Exit Sub
End If

' Examine the XML with the digital signature inserted
Debug.Print sbXml.GetAsString()

' Here is the output:

' <?xml version="1.0" encoding="utf-8"?>
' <abc>
'     <xyz>
'         <name>helloWorld.xml</name>
'         <url>https://www.chilkatsoft.com/data/helloWorld.xml</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/data/helloWorld.xml">
'       <ds:Transforms>
'         <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
'       </ds:Transforms>
'       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
'       <ds:DigestValue>H/s775OZhel6wdBhe02l4LK6m0lkplOisKxAbVwWxp0=</ds:DigestValue>
'     </ds:Reference>
'   </ds:SignedInfo>
'   <ds:SignatureValue>UruwnBqh..Ll4IzUA==</ds:SignatureValue>
'   <ds:KeyInfo>
'     <ds:X509Data>
'       <ds:X509Certificate>MIIHAz...nUZWCaDE=</ds:X509Certificate>
'     </ds:X509Data>
'   </ds:KeyInfo>
' </ds:Signature></xyz>
' </abc>

' Let's verify the signature...
Dim verifier As Chilkat.XmlDSig
Set verifier = Chilkat.NewXmlDSig
success = verifier.LoadSignatureSb(sbXml)
If (success <> True) Then
    Debug.Print verifier.LastErrorText
    Exit Sub
End If

' Let's examine the external references, and fetch the data for each..
Dim sbExternalData As Chilkat.StringBuilder
Set sbExternalData = Chilkat.NewStringBuilder

numRefs = verifier.NumReferences

i = 0
Do While i < numRefs

    bExternal = verifier.IsReferenceExternal(i)
    If (bExternal = True) Then

        uri = verifier.ReferenceUri(i)

        ' We're assuming the URI is an https:// or http:// URL...
        ' Let's also assume we know that the referenced data is text and we want the utf-8 byte representation.
        sbExternalData.Clear 
        success = http.QuickGetSb(uri,sbExternalData)
        If (success = False) Then
            Debug.Print http.LastErrorText
            Exit Sub
        End If

        ' Because the referenced external data was explicitly XML, it was the canonicalized XML that was digested.
        ' We need to canonicalize the XML in the same way as when signed.

        canonXml = verifier.CanonicalizeXml(sbExternalData.GetAsString(),"EXCL_C14N",False)
        success = sbExternalData.SetString(canonXml)

        success = verifier.SetRefDataSb(i,sbExternalData,"utf-8")
        If (success = False) Then
            Debug.Print verifier.LastErrorText
            Exit Sub
        End If

    End If

    i = i + 1
Loop

' Now that we have the external data available, we can verify the reference digest(s) and the signature.

bVerified = verifier.VerifySignature(True)
If (bVerified <> True) Then
    Debug.Print verifier.LastErrorText
    Exit Sub
End If

Debug.Print "Signature verified!"