_accessKey;
        $parameters['SignatureVersion'] = $this->_signatureVersion;
        $parameters['Version']          = $this->_apiVersion;
        $parameters['SignatureMethod']  = $this->_signatureMethod;
        if(!isset($parameters['Timestamp'])) {
            $parameters['Timestamp']    = gmdate('Y-m-d\TH:i:s\Z', time()+10);
        }
        $data = $this->_signParameters($url, $parameters);
        return $data;
    }
    /**
     * Set http request type to POST or GET
     * @param string $method
     */
    public function setHttpMethod($method = "POST") {
        $this->_httpMethod = strtoupper($method);
    }
    /**
     * Get the current http request type
     * @return string
     */
    public function getHttpMethod()
    {
        return $this->_httpMethod;
    }
    /**
     * 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 = $this->_httpMethod . "\n";
        $data .= parse_url($url, PHP_URL_HOST) . "\n";
        $data .= ('' == $path = parse_url($url, PHP_URL_PATH)) ? '/' : $path;
        $data .= "\n";
        uksort($paramaters, 'strcmp');
        unset($paramaters['Signature']);
        $arrData = array();
        foreach($paramaters as $key => $value) {
            $arrData[] = $key . '=' . str_replace('%7E', '~', rawurlencode($value));
        }
        $data .= implode('&', $arrData);
        $hmac = Zend_Crypt_Hmac::compute($this->_secretKey, 'SHA256', $data, Zend_Crypt_Hmac::BINARY);
        $paramaters['Signature'] = base64_encode($hmac);
        return $data;
    }
}