Well, security is a wide and growing field, so it would depend on a specific - in terms of what you want to secure when it comes to healthcare systems. Are you concerned primarily about Confidentiality, Integrity, or Access Control for the mobile health care system? You might have to look at Encryption Algorithms if you are mainly focused on Access Control, for example. On the other hand, you might want to look at Data Privacy algorithms and techniques, if your main goal is confidentiality of the data.