  Societies' norms of operation relies on the proper and secure functioning of
several critical infrastructures, particularly modern power grid which is also
known as smart grid. Smart grid is interwoven with the information and
communication technology infrastructure, and thus it is exposed to cyber
security threats. Intrusion tolerance proves a promising security approach
against malicious attacks and contributes to enhance the resilience and
security of the key components of smart grid, mainly SCADA and control centers.
Hence, an intrusion tolerant system architecture for smart grid control centers
is proposed in this paper. The proposed architecture consists of several
modules namely, replication & diversity, compromised/faulty replica detector,
reconfiuration, auditing and proxy. Some of distinctive features of the
proposed ITS are diversity as well as the combined and fine-grained
rejuvenation approach. The security of the proposed architecture is evaluated
with regard to availability and mean time to security failure as performance
measures. The analysis is conducted using a Discrete Time Semi Markov Model and
the acquired results show improvements compared to two established intrusion
tolerant architectures. The viability of SLA as another performance metric is
also investigated.
