(Visual FoxPro) Verify XML Signature with External Data Reference

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.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL lcUrl
LOCAL loHttp
LOCAL loSbXml
LOCAL lnSuccess
LOCAL loVerifier
LOCAL lcRefUri
LOCAL loJpgData
LOCAL lnBVerified

* 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..

lcUrl = "https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml"
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Http')
loHttp = CreateObject('Chilkat.Http')
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbXml = CreateObject('Chilkat.StringBuilder')
lnSuccess = loHttp.QuickGetSb(lcUrl,loSbXml)
IF (lnSuccess <> 1) THEN
    ? loHttp.LastErrorText
    RELEASE loHttp
    RELEASE loSbXml
    CANCEL
ENDIF

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.XmlDSig')
loVerifier = CreateObject('Chilkat.XmlDSig')

* 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.
lnSuccess = loVerifier.LoadSignatureSb(loSbXml)
IF (lnSuccess <> 1) THEN
    ? loVerifier.LastErrorText
    RELEASE loHttp
    RELEASE loSbXml
    RELEASE loVerifier
    CANCEL
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">
lcRefUri = loVerifier.ReferenceUri(0)
IF (loVerifier.LastMethodSuccess <> 1) THEN
    ? "No reference URI found."
    RELEASE loHttp
    RELEASE loSbXml
    RELEASE loVerifier
    CANCEL
ENDIF

* Download the JPG data to be verified.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.BinData')
loJpgData = CreateObject('Chilkat.BinData')
lnSuccess = loHttp.QuickGetBd(lcRefUri,loJpgData)
IF (lnSuccess <> 1) THEN
    ? loHttp.LastErrorText
    RELEASE loHttp
    RELEASE loSbXml
    RELEASE loVerifier
    RELEASE loJpgData
    CANCEL
ENDIF

* Provide the JPG data to the verifier
loVerifier.SetRefDataBd(0,loJpgData)

* Verify the signature
lnBVerified = loVerifier.VerifySignature(1)
? "Signature verified = " + STR(lnBVerified)

RELEASE loHttp
RELEASE loSbXml
RELEASE loVerifier
RELEASE loJpgData