The document proposes a secure and privacy-preserving opportunistic computing framework called SPOC for mobile healthcare emergencies. SPOC leverages spare resources on smartphones to process computationally intensive personal health information during emergencies while minimizing privacy disclosure. It introduces an efficient user-centric access control based on attribute-based access control and a new privacy-preserving scalar product computation technique to allow medical users to decide who can help process their data. Security analysis shows SPOC can achieve user-centric privacy control and performance evaluations show it provides reliable processing and transmission of personal health information while minimizing privacy disclosure during mobile healthcare emergencies.