_accessKey;
        $parameters['SignatureVersion'] = $this->_signatureVersion;
        $parameters['Version']          = $this->_apiVersion;
        if(!isset($parameters['Timestamp'])) {
            $parameters['Timestamp']    = gmdate('Y-m-d\TH:i:s\Z', time()+10);
        }
        $data = $this->_signParameters($url, $parameters);
        return $data;
    }
    /**
     * Computes the RFC 2104-compliant HMAC signature for request parameters
     *
     * This implements the Amazon Web Services signature, as per the following
     * specification:
     *
     * 1. Sort all request parameters (including SignatureVersion and
     *    excluding Signature, the value of which is being created),
     *    ignoring case.
     *
     * 2. Iterate over the sorted list and append the parameter name (in its
     *    original case) and then its value. Do not URL-encode the parameter
     *    values before constructing this string. Do not use any separator
     *    characters when appending strings.
     *
     * @param  string $queue_url  Queue URL
     * @param  array  $parameters the parameters for which to get the signature.
     *
     * @return string the signed data.
     */
    protected function _signParameters($url, array &$paramaters)
    {
        $data = '';
        uksort($paramaters, 'strcasecmp');
        unset($paramaters['Signature']);
        foreach($paramaters as $key => $value) {
            $data .= $key . $value;
        }
        $hmac = Zend_Crypt_Hmac::compute($this->_secretKey, 'SHA1', $data, Zend_Crypt_Hmac::BINARY);
        $paramaters['Signature'] = base64_encode($hmac);
        return $data;
    }
}