A protection profile for high-robustness separation ker- nels has recently been validated and several implementa- tions are under development. However, medium-robustness separation kernel development efforts have no protection profile, although the US Government has published guid- ance for authoring such a profile. As a step toward a protection profile, a set of security requirements for medium-robustness separation kernels is proposed. These requirements result from an informal, yet principled, approach. By bracketing the problem with ap- propriate reference points and elaborating a method for in- terpolating the requirements both a measure of uniformity and a basis for further discussion are achieved. Our refer- ence points include the high robustness protection profile, the existing medium robustness consistency instruction, and our familiarity with the nuances of separation kernels. This practitioner-oriented study is intended to advance the prevailing practices for commercial software develop- ment, which presently falls far short of the rigor needed for either high-robustness or medium-robustness systems. These requirements represent an incremental improvement in the pursuit of secure software -- and is intended to be a step forward on the road to higher assurance.