PureBasic

Verify XML Signature with External URL References

See more XML Digital Signatures Examples

Demonstrates how to verify an XML digital signature that includes references to URLs where the data to be digested is on a web server. PureBasic

IncludeFile "CkBinData.pb"
IncludeFile "CkHttp.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkXmlDSig.pb"

Procedure ChilkatExample()

    success.i = 0

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

    ; The signed XML we wish to verify contains external references such as this:

    ;     <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref0" 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:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref1" URI="https://www.chilkatsoft.com/hamlet.xml">
    ;       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
    ;       <ds:DigestValue>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</ds:DigestValue>
    ;     </ds:Reference>

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

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

    ; First load the signed XML
    sbSignedXml.i = CkStringBuilder::ckCreate()
    If sbSignedXml.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkStringBuilder::ckLoadFile(sbSignedXml,"qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml","utf-8")
    If success = 0
        Debug "Failed to load signed XML."
        CkXmlDSig::ckDispose(verifier)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbSignedXml)
        ProcedureReturn
    EndIf

    success = CkXmlDSig::ckLoadSignatureSb(verifier,sbSignedXml)
    If success = 0
        Debug CkXmlDSig::ckLastErrorText(verifier)
        CkXmlDSig::ckDispose(verifier)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbSignedXml)
        ProcedureReturn
    EndIf

    ; Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
    sbRefUri.i = CkStringBuilder::ckCreate()
    If sbRefUri.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

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

    numRefs.i = CkXmlDSig::ckNumReferences(verifier)
    i.i = 0
    While i < numRefs
        If CkXmlDSig::ckIsReferenceExternal(verifier,i) = 1
            CkStringBuilder::ckClear(sbRefUri)
            CkStringBuilder::ckAppend(sbRefUri,CkXmlDSig::ckReferenceUri(verifier,i))
            If CkStringBuilder::ckStartsWith(sbRefUri,"https://",0) = 1
                Debug "External URL Reference: " + CkStringBuilder::ckGetAsString(sbRefUri)

                ; Download the data at the URL and provide to the verifier.
                success = CkHttp::ckDownloadBd(http,CkStringBuilder::ckGetAsString(sbRefUri),bd)
                If success = 0
                    Debug CkHttp::ckLastErrorText(http)
                    CkXmlDSig::ckDispose(verifier)
                    CkHttp::ckDispose(http)
                    CkStringBuilder::ckDispose(sbSignedXml)
                    CkStringBuilder::ckDispose(sbRefUri)
                    CkBinData::ckDispose(bd)
                    ProcedureReturn
                EndIf

                success = CkXmlDSig::ckSetRefDataBd(verifier,i,bd)
                If success = 0
                    Debug CkXmlDSig::ckLastErrorText(verifier)
                    CkXmlDSig::ckDispose(verifier)
                    CkHttp::ckDispose(http)
                    CkStringBuilder::ckDispose(sbSignedXml)
                    CkStringBuilder::ckDispose(sbRefUri)
                    CkBinData::ckDispose(bd)
                    ProcedureReturn
                EndIf

            EndIf

        EndIf

        i = i + 1
    Wend

    ; Now that we have the external data, verify the signature..
    bVerified.i = CkXmlDSig::ckVerifySignature(verifier,1)
    If bVerified = 0
        Debug CkXmlDSig::ckLastErrorText(verifier)
    EndIf

    Debug "Signature verified = " + Str(bVerified)


    CkXmlDSig::ckDispose(verifier)
    CkHttp::ckDispose(http)
    CkStringBuilder::ckDispose(sbSignedXml)
    CkStringBuilder::ckDispose(sbRefUri)
    CkBinData::ckDispose(bd)


    ProcedureReturn
EndProcedure