SEMMI: Multi-party security decision-making scheme for linear functions in the internet of medical things

•The scheme does not require users’ original data to be exchanged and relies on homomorphic encryption to ensure data security during processing and transmission.•Each operation in the scheme is performed using encrypted data. To ensure that the normal business of trusted institutions is not affected, the amount of calculation is kept to a minimum.•The system’s security, execution efficiency, and final result accuracy are evaluated using both theoretical and experimental methods.