PureBasic

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.

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 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..

    url.s = "https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml"
    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

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

    success = CkHttp::ckQuickGetSb(http,url,sbXml)
    If success <> 1
        Debug CkHttp::ckLastErrorText(http)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbXml)
        ProcedureReturn
    EndIf

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

    ; 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 = CkXmlDSig::ckLoadSignatureSb(verifier,sbXml)
    If success <> 1
        Debug CkXmlDSig::ckLastErrorText(verifier)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbXml)
        CkXmlDSig::ckDispose(verifier)
        ProcedureReturn
    EndIf

    ; 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">
    refUri.s = CkXmlDSig::ckReferenceUri(verifier,0)
    If CkXmlDSig::ckLastMethodSuccess(verifier) <> 1
        Debug "No reference URI found."
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbXml)
        CkXmlDSig::ckDispose(verifier)
        ProcedureReturn
    EndIf

    ; Download the JPG data to be verified.
    jpgData.i = CkBinData::ckCreate()
    If jpgData.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkHttp::ckQuickGetBd(http,refUri,jpgData)
    If success <> 1
        Debug CkHttp::ckLastErrorText(http)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbXml)
        CkXmlDSig::ckDispose(verifier)
        CkBinData::ckDispose(jpgData)
        ProcedureReturn
    EndIf

    ; Provide the JPG data to the verifier
    CkXmlDSig::ckSetRefDataBd(verifier,0,jpgData)

    ; Verify the signature
    bVerified.i = CkXmlDSig::ckVerifySignature(verifier,1)
    Debug "Signature verified = " + Str(bVerified)


    CkHttp::ckDispose(http)
    CkStringBuilder::ckDispose(sbXml)
    CkXmlDSig::ckDispose(verifier)
    CkBinData::ckDispose(jpgData)


    ProcedureReturn
EndProcedure