In this paper we present five principles for designing ethically responsible offensive cyber security training. The principles can be implemented in existing or new study plans and target both academic and non-academic courses. Subject matter experts within various cyber security domains were consulted to validate and fine tune the principles, together with a literature review of ethical studies in related domains. The background for designing the principles is the continuous popularity of offensive cyber security (penetration testing, ethical hacking). Offensive cyber security means actively trying to break or compromise a system in order to find its vulnerabilities. If this expertise is placed in the wrong hands, the person can cause severe damage to organizations, civilians and society at large. The proposed ethical principles are created in order to mitigate these risks while maintaining the upsides of offensive cyber security. This is achieved by incorporating the ethical principles in offensive cyber security training, in order to facilitate the practitioners with ethical knowledge of how and when to use their acquired expertise.