failures, defects events, “human factors” or computer
viruses events on time line, etc.
To analyse an impact of information security on
the performance of standard processes there are
proposed the formalization for the general technology
used in process performance. The technology is based
on periodical diagnostics of modelled system
integrity, that is carried out to detect danger sources
penetration into a modelled system or consequences
of negative influences (see Figure 2). The lost
modelled system integrity can be detect only as a
result of diagnostics, after which the system recovery
is started. Dangerous influence on modelled system
is acted step-by step: at first a danger source
penetrates into the system and then after its activation
begins to influence. The system integrity can’t be lost
before penetrated danger source is activated. A
danger is considered to be realized only after a danger
source has influenced on the modelled system.
Figure 2: Some accident events in modelled system.
(left – correct operation, right – a lose of integrity
during prognostic period T
req
)
There are recommended some “Black box”
models for which probabilistic space (
, B, P) is
created (see for example Kostogryzov, 2008, 2012,
2020 etc.), where:
- is a limited space of elementary
events; B – a class of all subspace of
-space,
satisfied to the properties of
-algebra; P – is a
probability measure on a space of elementary events
. Because,
={
k
} is limited, there is enough to
establish a reflection
k
p
k
=P(
k
) like that p
k
0
and
1
k
k
p
.
It is supposed that used diagnostic tools allow to
provide necessary integrity recovery after revealing
danger sources penetration into modelled system or
the consequences of influences. Using the
probabilistic models (described in details in
Kostogryzov, 2008, 2012) the measures 𝑅
𝑇
and
𝑅
𝑇
can be estimated in terms “success” or
“failure” considering uncertainty conditions,
periodical diagnostics, monitoring between
diagnostics, recovery of the lost integrity for “Black
box”. There are the next input for probabilistic
modeling (Kostogryzov, 2008-2020):
- frequency of the occurrences of potential
threats (or mean time between the moments of the
occurrences of potential threats which equals to
1/frequency);
- mean activation time of threats;
T
betw
- time between the end of diagnostics and the
beginning of the next diagnostics;
T
diag
- diagnostics time;
T
recov
- recovery time
T - given prognostic period.
3.2.2 About Modeling for Complex System
For a complex systems with parallel or serial
structure there are proposed the next method to
generate adequate probabilistic models
(Kostogryzov, 2008-2020 etc.) This method uses the
usual way of probability theory for independent
random variables, it is described below.
Let's consider the elementary structure from two
independent parallel or series elements. Let’s PDF of
time between losses of i-th element integrity is В
i
(t)
=Р (τ
i
≤ t), then:
1) time between losses of integrity for modelled
system combined from series connected independent
elements is equal to a minimum from two times τ
i
:
failure of 1st or 2nd elements (i.e. the modelled
system goes into a state of lost integrity when either
1st, or 2nd element integrity is lost). For this case the
PDF of time between losses of modelled system
integrity is defined by expression
В(t) = Р[min (τ
1
,τ
2
)≤t] =1- Р[min (τ
1
,τ
2
)>t] =
= 1- Р(τ
1
>t)Р(τ
2
> t)= 1 – [1-В
1
(t)] [1- В
2
(t)], (3)
2) time between losses of integrity for modelled
system combined from parallel connected
independent elements (hot reservation) is equal to a
maximum from two times τ
i
: failure of 1st and 2nd
elements (i.e. the modelled system goes into a state of
lost integrity when both 1st and 2nd elements have
lost integrity). For this case the PDF of time between
losses of modelled system integrity is defined by
expression
В(t)=Р[max(τ
1
,τ
2
)≤t]=Р(τ
1
≤t)Р(τ
2
≤t)=В
1
(t)В
2
(t)
(4)
Applying recurrently expressions (3) – (4), it is
possible to build PDF of time between losses of
integrity for any complex system with parallel and/or
series structure and theirs combinations.
Using these probabilistic models and methods
(described in details in […]) the measures 𝑅
𝑇
and 𝑅
𝑇
can be estimated in terms “success” or
“failure” considering uncertainty conditions, system
INFSEC 2021 - International Scientific and Practical Conference on Computer and Information Security