Security of Safety Important I&C Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 264

Table 4. Effectiveness evaluation matrix for security countermeasures

Attack Available Countermeasures

m 1 m 2 … m n

ep 1 eh 1 et 1 ep 2 eh 2 et 2 … ep n eh n et n

a 1 0 1 1 0 0 0 … 1 0 0

a 2 0 1 0 1 0 0 … 0 0 0

… … … … … … … … … … …

a k 1 1 0 0 1 0 … 1 1 0

Table 5. Integral evaluation of security countermeasures effectiveness

Available countermeasures

Attack m 1 m 2 … m n

e 1 c 1 e 2 c 2 … e n c n

a 1 2 c 1,1 0 c 1,2 … 1 c 1,n

a 2 1 c 2,1 1 c 2,2 … 0 c 2,n

… … … … … … … …

a k 2 c k,1 1 c k,2 … 1 c k,n

includes integral effectiveness of the countermea-
sures compared to each of the possible attacks.
Application of the specific security counter-
measure requires certain costs. Hence, such costs
will depend on the chosen countermeasure and
appropriate attack type. Costs of certain counter-
measure application can be defined in a form of
table, as well as integral effectiveness (see Table
5).

First problem is actual for I&C systems of
critical application and can be formulated in the
following way:

m n

( ) =

∑ ,

f x c x = → cx min, x D ∈ (4)

i j i j ,

i = 1 j = 1

n

∈ { }

∑

D = x R ∈

mn

| e ⋅ x + > d CR i , ∈ 1 , m x ; 0 1 ,

i j , i j , i i j ,

j = 1

A problem of optimal choice of security coun-
termeasures can be solved in two ways:

(5)

where d i is initial level of i -th attack type criticality;
CR is a number that defines criticality diagonal;
e i,j is effectiveness of j -th countermeasure ap-
plication to i -th attack type; c i,j is costs of j -th
countermeasure application to decrease criticality
of i -th attack type.
Initial level of i -th attack type criticality is set
with some value, as well as criticality diagonal,
and is defined by a position within criticality

1. Minimization of costs associated with
purchasing and implementation of counter-
measures in order to decrease the criticality
for all possible attack types down to some
predefined level.
2. Maximal possible decreasing of attacks
criticality within the predefined limits for
appropriate costs.