The growing number of software and hardware system attacks has made security a critical factor in their design. To guarantee the safety of the system, security requirements must be established, but this is a difficult task since they are usually expressed in natural language. Researchers have proposed structured natural language templates for specifying security requirements to simplify this process. These templates must consider various security aspects, such as security criteria and mechanisms. This paper introduces the SECurity REquirements specificaTion (SECRET) template, developed through two action research cycles to address these issues. Initially, the SECRET template was created and tested by identifying and resolving problems in defining security requirements. Then, the SECRET template was applied to a use case, and it was concluded that all security requirements were correctly specified.