1. Design of the multi-level security network switch system which restricts covert channel Conference: Communication Software and Networks (ICCSN), 2011 IEEE 3rd International Conference on Authors: Xiong Liu, Haiwei Xue, Xiaoping Feng, Yiqi Dai, Department of Computer Science and Technology, Tsinghua University, Beijing 10084, China 1

2. Covert channel In computer security, a covert channel is a type of computer security attack that creates a capability to transfer information objects between processes that are not supposed to be allowed to communicate by the computer security policy. 2

3. Multi-level Security Local Area Network system (MSL) The low level host can send data packet to high level host, but high level host cannot send data packet to low level host. TCP/IP SYN/ACK packet cannot be sent back in the above mechanism. So it must allow the sending of SYN/ACK. The SYN/ACK may become a loophole for the covert channel. 3 Low level High level host

4. System architecture Monitor in each hosts Controller Filter 4

5. System architecture- Monitor The system can monitor the hosts’ actions to specify the hosts’ security level by the monitors. The user must install the monitor in their computer. Monitor communicate to the controller. 5

6. System architecture- controller Functions: –Host registering: Make sure that all the hosts and switches connected to the network are authorized. –Flow computing: Compute the packet’s flow path based on the network’s topological structure. It can make sure all of the data flow paths are compatible with the system’s security policy 6 Level: 2Level: 3

7. System architecture- controller (cont.d) –Flow updating: When the flow path has been computed, the Controller updates the flow tables of switches which locate on the path to set up it. 7

8. System architecture- filter Content check module –Level 1: Check the data field and flags field. –Level 2: Check the unused fields and optional field. –Level 3: Check the sequence number and acknowledgement number. –Level 4: Check the covert channel which uses packet retransmission or packet loss to send information. 8

9. Experiment 9

10. Conclusion This paper proposed a design of multi- level security network switch system which can restrict covert channel. The design can guarantee the availability and security of the information exchange among hosts in multi-level security network system. The experiment showed that the design is available. 10

11. Reference http://en.wikipedia.org/wiki/Covert_channel [L-BLP security model in local area network],http://www.ejournal.org.cn/CN/ab stract/abstract44.shtmlhttp://www.ejournal.org.cn/CN/ab stract/abstract44.shtml 11