Method and system for encrypting streamed data employing fast set-up single use keys and self-synchronization. Each filter is formed by applying a DC electric field to the gas stream which causes the ions to move in a direction opposite to the gas flow. The invention can be implemented to expand a narrow-neck preform or container finish to a wide-mouth preform or container finish. The invention can effectively avoid the problem of electric discharge when RF signals transmit in a vacuum chamber, resulting in more security and less transmission power loss.