A method for secure communications over a public fiber- optical network

We develop a spread-spectrum based approach to secure communications over existing fiber-optical networks. Secure transmission for a dedicated user is achieved by overlaying a covert channel onto a host channel in the existing active fiber link. The covert channel is optically encoded and temporally spread, and has average power below the noise floor in the fiber, making it hidden for a direct detection thus allowing for cryptographic and steganographic security capabilities. The presence for the host channel in the network provides an ad hoc security expansion and increases the difficulty for an eavesdropper to intercept and decode the secure signal. (c) 2006 Optical Society of America.