The presence of communication networks inside load frequency control loops exposes them to cyber–physical attacks, particularly denial-of-service and deception attacks. Potential cyber–physical attacks on power systems degrade the control performance or even cause instability. This paper proposes a blockchain-based solution against denial-of-service attacks to secure resilient smart systems. A multi-area-based PI-controllers microgrid system is examined. To protect access to the shared blockchain, a proof-of-work private blockchain approach is developed. During denial-of-service attacks, the proof-of-work based blockchain approach safeguards a copy of all data amongst smart grid parts and thus restores the true information. An H∞ control approach is developed to mitigate the uncertainty of the denial-of-service intrusions. Numerical simulations demonstrate the superiority of the proposed blockchain based H∞ controller in comparison to traditional controllers in safeguarding power systems against denial-of-service attacks.