Robust encryption for secure image transmission over wireless channels

The security of multimedia data transmitted over wireless networks is of increased interest. Encryption mechanisms securely transmit multimedia data over insecure networks. A major issue that has received very little attention so far is that the very same properties that gives ciphers (encryption mechanisms) their cryptographic strength make them sensitive to channel errors as well. In addition, this would enhance the error propagation inherent in compressed data. Therefore provision of security for multimedia transmission over wireless channel results in throughput loss. Nevertheless this lost throughput is traded for increased security. To our knowledge there has been no substantial effort to optimize this tradeoff. Opportunistic encryption proposed in this work is a way to optimize the tradeoff between security offered and the throughput lost due to a cipher. We show that opportunistic encryption methods that adapt to channel variations will lead to an overall increase in the system performance. Two broad scenarios based on channel knowledge are considered, (a) exact channel state information up to a finite time horizon is known and (b) only the average signal-to-noise ratio (SNR) is known. Proposed opportunistic encryption framework is found to achieve significant gains in throughput compared to fixed block length encryption methods for a wide range of average SNR values. We have shown that applying opportunistic encryption on JPEG compressed image results in a better quality of received image and improved security compared to fixed block length encryption.