Information Technology Reference
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sert or loss of packets). If we assume, that there are a few mistakes, the excess of the
number of even distances over the given threshold can be considered, as the signal to
the agent to become active and to begin the following stage of reception of the in-
structions from the adversary in a global network.
The procedure of the transition of a natural parameter
k
or to allocate
k
of the given
sets of addresses {
f
−
−
(
s
) ,…,
f
(
s
)} does not differ from the procedure of activa-
tion of an agent.
Determination of these parameters allows for construction of
some languages for
transmission of covert information from PC(0,2) to PC(0,1).
Let
k
=2. In the first language PC(0,2) uses code for 1 with a pair of packets with
source addresses
s
and
s
so, that
s
is on an odd place (concerning the fixed be-
ginning of a flow), and
s
- on an even place. Code for 0 demands to place a packet
with
s
on an even place, and a packet with
s
on an odd place. In intervals between
the packets with source addresses
s
it is possible to insert any sequences of
other packets, which are not breaking the specified rules.
Let
k
=3 and a monotonously growing sequence of addresses
s
,
s
,
s
means 1.
A monotonously decreasing sequence of addresses
s
,
s
,
s
means 0. The loss or
insert of one of these addresses in a combination of 0 or 1 follows revealing of a mis-
take. Thus packets with other addresses can be arbitrary placed between the packets
with addresses of a code.
To transfer the information by the ordered vectors of addresses of length
k
(
k
is
known) it is necessary to carry out training. We consider, that the set
S
is linearly
ordered for example,
s
<
s
< … <
s
. The procedure of training is necessary to
restore at PC(0,1) the order ≤ on set
f
−
(
S
). Thus we consider, that if
x
and
y
belong
f
−
(
s
), then
x = y
. The procedure of training consists of the following. Having re-
ceived
k
from packets with source addresses
s
and
s
, PC(0,2) orders them
according to the relation ≤ (less or equally) and sends the given packets to the protec-
tion device for the subsequent transfer to PC(0,1).
The opportunity of feedback from PC(0,1) to PC(0,2) is the essential acceleration
of the training procedure of the agents at PC(0,1). Such acceleration uses a leaving
flow of packets, in which the destination addresses repeat a sequence transferred from
PC(0,2) to PC(0,1).
,
s
, …,
s
3
Some Properties of the Covert Channels
Let's consider the problem of revealing the existence of the covert channel by the
warden. Let the warden
U
be in PD(
i
) and calculate frequency of pairs of addresses
in a flow of packets with the purpose of revealing the covert channel between PC(
i
,2)
and PC(
i
,1),
. Activation of the agent can be revealed by supervision of
pairs of addresses. When the described method of activation is used any pair of ad-
dresses (
s
,
s
) cannot appear.
=
