/**
     * Downloads a CRL from given LDAP url, e.g.
     * ldap://ldap.infonotary.com/dc=identity-ca,dc=infonotary,dc=com
     */
    private static X509CRL downloadCRLFromLDAP(String ldapURL) throws CertificateException, 
    NamingException, CRLException,
            CertificateVerificationException {
        Map<String, String> env = new Hashtable<String, String>();
        env.put(Context.INITIAL_CONTEXT_FACTORY,
                "com.sun.jndi.ldap.LdapCtxFactory");
        env.put(Context.PROVIDER_URL, ldapURL);

        DirContext ctx = new InitialDirContext((Hashtable)env);
        Attributes avals = ctx.getAttributes("");                            //строка, в которой кидается исключение
        Attribute aval = avals.get("certificateRevocationList;binary");
        byte[] val = (byte[]) aval.get();
        if ((val == null) || (val.length == 0)) {
            throw new CertificateVerificationException(
                    "Can not download CRL from: " + ldapURL);
        } else {
            InputStream inStream = new ByteArrayInputStream(val);
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            return (X509CRL) cf.generateCRL(inStream);
        }
    }