  Increasing volatilities within power transmission and distribution force
power grid operators to amplify their use of communication infrastructure to
monitor and control their grid. The resulting increase in communication creates
a larger attack surface for malicious actors. Indeed, cyber attacks on power
grids have already succeeded in causing temporary, large-scale blackouts in the
recent past. In this paper, we analyze the communication infrastructure of
power grids to derive resulting fundamental challenges of power grids with
respect to cybersecurity. Based on these challenges, we identify a broad set of
resulting attack vectors and attack scenarios that threaten the security of
power grids. To address these challenges, we propose to rely on a
defense-in-depth strategy, which encompasses measures for (i) device and
application security, (ii) network security, (iii) physical security, as well
as (iv) policies, procedures, and awareness. For each of these categories, we
distill and discuss a comprehensive set of state-of-the art approaches, and
identify further opportunities to strengthen cybersecurity in interconnected
power grids.
