PHP

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. Chilkat2 PHP

<?php

use Chilkat2\BinData;
use Chilkat2\Http;
use Chilkat2\StringBuilder;
use Chilkat2\XmlDSig;

// 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 = new XmlDSig();
$http = new Http();

// First load the signed XML
$sbSignedXml = new StringBuilder();
try {
    $sbSignedXml->LoadFile('qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml', 'utf-8');
} catch (\Chilkat2\Exception $e) {
    echo "Failed to load signed XML.\n";
    exit;
}

try {
    $verifier->LoadSignatureSb($sbSignedXml);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

// Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
$sbRefUri = new StringBuilder();
$bd = new BinData();
$numRefs = $verifier->NumReferences;
$i = 0;
while ($i < $numRefs) {
    if ($verifier->IsReferenceExternal($i)) {
        $sbRefUri->Clear();
        $sbRefUri->Append($verifier->ReferenceUri($i));
        if ($sbRefUri->StartsWith('https://', false)) {
            echo 'External URL Reference: ', $sbRefUri->GetAsString(), "\n";

            // Download the data at the URL and provide to the verifier.
            try {
                $http->DownloadBd($sbRefUri->GetAsString(), $bd);

                $verifier->SetRefDataBd($i, $bd);
            } catch (\Chilkat2\Exception $e) {
                echo $e->getMessage(), "\n";
                exit;
            }
        }
    }

    $i = $i + 1;
}

// Now that we have the external data, verify the signature..
try {
    $verifier->VerifySignature(true);
    $bVerified = true;
} catch (\Chilkat2\Exception $e) {
    $bVerified = false;
}
if (!$bVerified) {
    echo $verifier->LastErrorText, "\n";
}

echo 'Signature verified = ', ($bVerified ? 'true' : 'false'), "\n";