(PureBasic) Create/Verify XML Signature with External Text Reference

See more XML Digital Signatures Examples

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

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IncludeFile "CkHttp.pb"
IncludeFile "CkXml.pb"
IncludeFile "CkXmlDSig.pb"
IncludeFile "CkXmlDSigGen.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkCert.pb"

Procedure ChilkatExample()

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

    ; This example inserts an XML signature into the following XML:

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

    ; Build the above XML to be signed.
    xml.i = CkXml::ckCreate()
    If xml.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkXml::setCkTag(xml, "abc")
    CkXml::ckUpdateChildContent(xml,"xyz|name","helloWorld.txt")
    CkXml::ckUpdateChildContent(xml,"xyz|url","https://www.chilkatsoft.com/helloWorld.txt")

    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkCert::ckLoadPfxFile(cert,"qa_data/pfx/test_secret.pfx","secret")
    If success = 0
        Debug CkCert::ckLastErrorText(cert)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    gen.i = CkXmlDSigGen::ckCreate()
    If gen.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Indicate the location within the XML the Signature will be inserted.
    CkXmlDSigGen::setCkSigLocation(gen, "abc|xyz")

    ; Get the content of the text data to be referenced.
    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    sbExternalTxt.i = CkStringBuilder::ckCreate()
    If sbExternalTxt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkHttp::ckQuickGetSb(http,"https://www.chilkatsoft.com/helloWorld.txt",sbExternalTxt)
    If success = 0
        Debug CkHttp::ckLastErrorText(http)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        ProcedureReturn
    EndIf

    success = CkXmlDSigGen::ckAddExternalTextRef(gen,"https://www.chilkatsoft.com/helloWorld.txt",sbExternalTxt,"utf-8",0,"sha256","")
    If success = 0
        Debug CkXmlDSigGen::ckLastErrorText(gen)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        ProcedureReturn
    EndIf

    ; Provide the private key for signing via the certificate, and indicate that
    ; we want the base64 of the certificate embedded in the KeyInfo.
    CkXmlDSigGen::setCkKeyInfoType(gen, "X509Data")
    CkXmlDSigGen::setCkX509Type(gen, "Certificate")

    bUsePrivateKey.i = 1
    success = CkXmlDSigGen::ckSetX509Cert(gen,cert,bUsePrivateKey)
    If success <> 1
        Debug CkXmlDSigGen::ckLastErrorText(gen)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        ProcedureReturn
    EndIf

    ; Indicate we want an indented signature for readability.
    ; This can be removed after debugging is finished..
    CkXmlDSigGen::setCkBehaviors(gen, "IndentedSignature")

    ; Now create and insert the Signature
    sbXml.i = CkStringBuilder::ckCreate()
    If sbXml.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkXml::ckGetXmlSb(xml,sbXml)
    success = CkXmlDSigGen::ckCreateXmlDSigSb(gen,sbXml)
    If success <> 1
        Debug CkXmlDSigGen::ckLastErrorText(gen)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        CkStringBuilder::ckDispose(sbXml)
        ProcedureReturn
    EndIf

    ; Examine the XML with the digital signature inserted
    Debug CkStringBuilder::ckGetAsString(sbXml)

    ; Here is the output:

    ; <?xml version="1.0" encoding="utf-8"?>
    ; <abc>
    ;     <xyz>
    ;         <name>helloWorld.txt</name>
    ;         <url>https://www.chilkatsoft.com/helloWorld.txt</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/helloWorld.txt">
    ;       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
    ;       <ds:DigestValue>f4OxZX/x/FO5LcGBSKHWXfwtSx+j1ncoSt3SABJtkGk=</ds:DigestValue>
    ;     </ds:Reference>
    ;   </ds:SignedInfo>
    ;   <ds:SignatureValue>syFSl...pZDiFQ==</ds:SignatureValue>
    ;   <ds:KeyInfo>
    ;     <ds:X509Data>
    ;       <ds:X509Certificate>MIIHAz...GwnUZWCaDE=</ds:X509Certificate>
    ;     </ds:X509Data>
    ;   </ds:KeyInfo>
    ; </ds:Signature></xyz>
    ; </abc>

    ; Let's verify the signature...
    verifier.i = CkXmlDSig::ckCreate()
    If verifier.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkXmlDSig::ckLoadSignatureSb(verifier,sbXml)
    If success <> 1
        Debug CkXmlDSig::ckLastErrorText(verifier)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        CkStringBuilder::ckDispose(sbXml)
        CkXmlDSig::ckDispose(verifier)
        ProcedureReturn
    EndIf

    ; Let's examine the external references, and fetch the data for each..
    sbExternalData.i = CkStringBuilder::ckCreate()
    If sbExternalData.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    numRefs.i = CkXmlDSig::ckNumReferences(verifier)
    i.i = 0
    While i < numRefs
        bExternal.i = CkXmlDSig::ckIsReferenceExternal(verifier,i)
        If bExternal = 1
            uri.s = CkXmlDSig::ckReferenceUri(verifier,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.
            CkStringBuilder::ckClear(sbExternalData)
            success = CkHttp::ckQuickGetSb(http,uri,sbExternalData)
            If success = 0
                Debug CkHttp::ckLastErrorText(http)
                CkXml::ckDispose(xml)
                CkCert::ckDispose(cert)
                CkXmlDSigGen::ckDispose(gen)
                CkHttp::ckDispose(http)
                CkStringBuilder::ckDispose(sbExternalTxt)
                CkStringBuilder::ckDispose(sbXml)
                CkXmlDSig::ckDispose(verifier)
                CkStringBuilder::ckDispose(sbExternalData)
                ProcedureReturn
            EndIf

            success = CkXmlDSig::ckSetRefDataSb(verifier,i,sbExternalData,"utf-8")
            If success = 0
                Debug CkXmlDSig::ckLastErrorText(verifier)
                CkXml::ckDispose(xml)
                CkCert::ckDispose(cert)
                CkXmlDSigGen::ckDispose(gen)
                CkHttp::ckDispose(http)
                CkStringBuilder::ckDispose(sbExternalTxt)
                CkStringBuilder::ckDispose(sbXml)
                CkXmlDSig::ckDispose(verifier)
                CkStringBuilder::ckDispose(sbExternalData)
                ProcedureReturn
            EndIf

        EndIf

        i = i + 1
    Wend

    ; Now that we have the external data available, we can verify the reference digest(s) and the signature.
    bVerified.i = CkXmlDSig::ckVerifySignature(verifier,1)
    If bVerified <> 1
        Debug CkXmlDSig::ckLastErrorText(verifier)
        CkXml::ckDispose(xml)
        CkCert::ckDispose(cert)
        CkXmlDSigGen::ckDispose(gen)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbExternalTxt)
        CkStringBuilder::ckDispose(sbXml)
        CkXmlDSig::ckDispose(verifier)
        CkStringBuilder::ckDispose(sbExternalData)
        ProcedureReturn
    EndIf

    Debug "Signature verified!"


    CkXml::ckDispose(xml)
    CkCert::ckDispose(cert)
    CkXmlDSigGen::ckDispose(gen)
    CkHttp::ckDispose(http)
    CkStringBuilder::ckDispose(sbExternalTxt)
    CkStringBuilder::ckDispose(sbXml)
    CkXmlDSig::ckDispose(verifier)
    CkStringBuilder::ckDispose(sbExternalData)


    ProcedureReturn
EndProcedure