Real-time applications with security requirements are emerging in various areas including government, education, and business. The security sensitive real-time applications can take full advantage of a grid environment that allows grid participants to exercise a fine-grained control and allocation of computational resources. However, conventional real-time scheduling algorithms failed to fulfil the security requirements of real-time applications. In this paper we propose a dynamic realtime scheduling algorithm, or SAREG, which is capable of enhancing quality of security for real-time applications running on Grids. To make SAREG practical, we present a mathematical model to formally describe a scheduling framework, security-sensitive real-time applications, and security overheads. We leverage the model to measure security overheads incurred by an array of security services, including encryption, authentication, integrity check, etc. The SAREG algorithm seamlessly integrates security re...