XMLSecurityDSig::validateReference PHP Method

    public function validateReference()
    {
        $docElem = $this->sigNode->ownerDocument->documentElement;
        if (!$docElem->isSameNode($this->sigNode)) {
            $this->sigNode->parentNode->removeChild($this->sigNode);
        }
        $xpath = $this->getXPathObj();
        $query = "./secdsig:SignedInfo/secdsig:Reference";
        $nodeset = $xpath->query($query, $this->sigNode);
        if ($nodeset->length == 0) {
            throw new Exception("Reference nodes not found");
        }
        /* Initialize/reset the list of validated nodes. */
        $this->validatedNodes = array();
        foreach ($nodeset as $refNode) {
            if (!$this->processRefNode($refNode)) {
                /* Clear the list of validated nodes. */
                $this->validatedNodes = null;
                throw new Exception("Reference validation failed");
            }
        }
        return true;
    }

 /**
  * @return bool
  * @throws Exception
  */
 public function isValid()
 {
     $objXMLSecDSig = new XMLSecurityDSig();
     $objDSig = $objXMLSecDSig->locateSignature($this->_document);
     if (!$objDSig) {
         throw new Exception('Cannot locate Signature Node');
     }
     $objXMLSecDSig->canonicalizeSignedInfo();
     $objXMLSecDSig->idKeys = array('ID');
     $retVal = $objXMLSecDSig->validateReference();
     if (!$retVal) {
         throw new Exception('Reference Validation Failed');
     }
     $singleAssertion = $this->validateNumAssertions();
     if (!$singleAssertion) {
         throw new Exception('Multiple assertions are not supported');
     }
     $validTimestamps = $this->validateTimestamps();
     if (!$validTimestamps) {
         throw new Exception('Timing issues (please check your clock settings)
         ');
     }
     $objKey = $objXMLSecDSig->locateKey();
     if (!$objKey) {
         throw new Exception('We have no idea about the key');
     }
     XMLSecEnc::staticLocateKeyInfo($objKey, $objDSig);
     $objKey->loadKey($this->_settings->idpPublicCertificate, FALSE, TRUE);
     return $objXMLSecDSig->verify($objKey) === 1;
 }