Covert Communication Techniques Based On Network Flow

With the increasing information being shared and transmitted through communication networks, network security is becoming more and more crucial for securing information. Information may be stolen or tampered while being processed or transmitted, resulting in huge losses. Especially for national security, once the confidential information is attacked, the consequences could be disastrous. Although information can be protected using cryptography, the ciphertext can be easily noticed by attackers. Moreover, with the rapid development of decipher technology and computer hardware, the performance of deciphering has been greatly improved, presenting a big challenge to existing cryptography technology. Therefore, a new technology called information hiding techniques has been proposed. As a branch of information security technology, information hiding technology aims to protect the secret information by hiding confidential information behind some information carriers. Since a lot of data streams are transmitted by communication networks, such network packet streams can be utilized as a ideal carrier for hidden communication.After analyzing existing covert communications based on Internet protocols, this paper focuses on the design and implementation of covert timing channels. Based on the modeling and analysis of covert timing channels, information theory was utilized to analyze the performance of covert timing channels. To improve the efficiency of covert channels, an adaptive receiving covert timing channel was proposed and implemented. Furthermore, in order to improve the secrecy of the covert channel, a novel covert timing channel based on simulating packet flow characteristics was further proposed.The proposed covert timing channels are implemented on Linux platform, which are based on network packet flows. The performance is verified by testing and comparing with the general ones. Both the theoretical and empirical results demonstrated that the proposed covert timing channels can be effectively used to transmitted confidential information. Furthermore, this paper also points out the direction of future research.