Abstract: Cloud computing has an inherent cyber security weakness and vulnerability to insider attacks that comes with the shared security responsibility model practiced by cloud providers. We developed a secure and trustworthy cloud computing and outsourcing security framework for power grid applications, with associated computational algorithms and software tools, to prevent and mitigate cyber-attacks and achieve resilience of cloud-based power grid applications. The approach is to use information masking and integrity-preserving mathematical transformation to alter the power system problems into unrecognizable computing jobs on clouds, protecting sensitive data and critical information from cloud security breach such as insider attack.