function loadCA($cert)
    {
        $olddn = $this->dn;
        $oldcert = $this->currentCert;
        $oldsigsubj = $this->signatureSubject;

        $cert = $this->loadX509($cert);
        if (!$cert) {
            $this->dn = $olddn;
            $this->currentCert = $oldcert;
            $this->signatureSubject = $oldsigsubj;

            return false;
        }

        /* From RFC5280 "PKIX Certificate and CRL Profile":

           If the keyUsage extension is present, then the subject public key
           MUST NOT be used to verify signatures on certificates or CRLs unless
           the corresponding keyCertSign or cRLSign bit is set. */
        //$keyUsage = $this->getExtension('id-ce-keyUsage');
        //if ($keyUsage && !in_array('keyCertSign', $keyUsage)) {
        //    return false;
        //}

        /* From RFC5280 "PKIX Certificate and CRL Profile":

           The cA boolean indicates whether the certified public key may be used
           to verify certificate signatures.  If the cA boolean is not asserted,
           then the keyCertSign bit in the key usage extension MUST NOT be
           asserted.  If the basic constraints extension is not present in a
           version 3 certificate, or the extension is present but the cA boolean
           is not asserted, then the certified public key MUST NOT be used to
           verify certificate signatures. */
        //$basicConstraints = $this->getExtension('id-ce-basicConstraints');
        //if (!$basicConstraints || !$basicConstraints['cA']) {
        //    return false;
        //}

        $this->CAs[] = $cert;

        $this->dn = $olddn;
        $this->currentCert = $oldcert;
        $this->signatureSubject = $oldsigsubj;

        return true;
    }