  Recent cyber-attacks on power grids highlight the necessity to protect the
critical functionalities of a control center vital for the safe operation of a
grid. Even in a distributed framework one central control center acts as a
coordinator in majority of the control center architectures. Such a control
center can become a prime target for cyber as well as physical attacks, and,
hence, a single point failure can lead to complete loss of visibility of the
power grid. If the control center which runs the critical functions in a
distributed computing environment can be randomly chosen between the available
control centers in a secure framework, the ability of the attacker in causing a
single point failure can be reduced to a great extent. To achieve this, a novel
distributed hierarchy based framework to secure critical functions is proposed
in this paper. The proposed framework ensures that the data aggregation and the
critical functions are carried out at a random location, and incorporates
security features such as attestation and trust management to detect
compromised agents. A theoretical result is proved on the evolution and
convergence of the trust values in the proposed trust management protocol. It
is also shown that the system is nominally robust so long as the number of
compromised nodes is strictly less than one-half of the nodes minus 1. For
demonstration, a Kalman filter-based state estimation using phasor measurements
is used as the critical function to be secured. The proposed framework's
implementation feasibility is tested on a physical hardware cluster of
Parallella boards. The framework is also validated using simulations on the
IEEE 118 bus system.
