Abstract
The communication network has experienced enormous growth in the past few decades. The growth of communication network requires the data to be transmitted at a high speed as well as in a secure scheme. The traditional ways of providing communication security are based on the existing network infrastructure. These methods consume the capacity of the network and thus the security is achieved at the cost of transmission speed. Moreover, since the network infrastructure in the physical layer is not designed for security purpose, protection schemes based on the infrastructure is limited by its functions and cannot achieve ideal and effective protection. This thesis focuses on optical steganography and optical encryption techniques to improve the physical infrastructure of the communication network for secure purpose. The network is effectively protected without compromising the transmission speed.
Optical steganography methods in which amplifier noise is used as the signal carrier are proposed and experimentally demonstrated. Since the optical amplifiers are widely used in the fiber optic network, using the amplifier noise as the signal carrier creates extra network capacity without consuming extra power. The noise carried signals are effectively hidden in both time domain and frequency domain. To deploy optical steganography in the communication network, the system performances of the stealth channel, including the bit error rate (BER) and dispersion effect are theoretically analyzed and experimentally demonstrated. Besides optical steganography, an optical encryption method is demonstrated. The encrypted signal is protected by analog radio frequency noise. Without decrypting the signal in real time, the data cannot be digitized and will be loss permanently.
The security techniques studied in this thesis can solve security problems that cannot be solved by the traditional software based methods. On the other hand, the functions of physical layer techniques can be optimized if physical layer techniques are combined with the traditional software based techniques. This thesis studies the software interface between physical layer techniques and application level network. Steganography Assisted Tor (SAT) is demonstrated as an interface and it can effectively protect the privacy and anonymity of the network.