6th European Conference - Academic Conferences

Hind Al Falasi and Liren Zhang
therefore, creating a covert channel diminishes. The service time at the high security network is the
only factor under the control of the high security network. The other elements are controlled by the
physical environment of the network. On the other hand, if the distance between them is small, we
estimate that the i th packet is deleted from the buffer at α1 + T1 + T2 + 1/ µ2.
Another element to consider is the high security network service time, which affects the SAFP
queuing time. We are considering this element because it leads to the establishment of a timing
covert channel between the high security network and the low security network. A slow service time
eventually leads to a full buffer at the SAFP. In other words, packets from the low security network are
lost; therefore, no acknowledgments are sent from the SAFP to the low security network. From there,
the high security network can control the SAFP buffer; subsequently, it can control the rate of the
acknowledgments from the SAFP to the low security network. Therefore, it can use the delays to
signal messages to the low security network. The SAFP buffer is modeled using the M/M/1/K model
as it has a finite capacity where the maximum number of packets in the buffer is K. A packet enters
the queue if it finds fewer than K packets in the buffer and is lost otherwise. The probability of a full
buffer = blocking probability = probability of a covert channel. An illustration of the above scenario is
presented in Figure 2.
Figure 2: Communication representation between low security network, SAFP and high security
network
5. Analysis of the system using Markov chain model
Using the state transition diagram (see Figure 3), we found the blocking probability of the SAFP buffer
(PK):
Solving the equations in terms of P0:
p
p
p
(
1
2
k
1
2
p
1
0
p
K
1
2
1
2
1
2
2
p
0
2
k
2
) p
1
p
p
k
p
1
p
0
0
K 1
1
p
k 1
k
k
P
K
0
1
2
p
1
2
k 1
K
p
0
k
1
k
0
k
K
K
1
11
(1)
(2)
(3)