On the use of TEE for mission critical public safety use cases

Standards developed for Mission Critical Services (MCS) to serve Public Safety (PS) over Long-Term Evolution (LTE) in 3GPP Release 12 and 13 define the security requirements which are founded on principles used for Commercial LTE networks. Deployment models, applications and use cases for PS vary significantly from commercial networks. Hence, more sophisticated security mechanisms to facilitate use cases related to provisioning and service activation that are beyond regular commercial use. Existing user authentication is based on the use of a Universal Services Identity Module (USIM) application running a secure element within a single Universal Integrated Circuit Card (UICC) card. Single user binding to a SIM card and device becomes restrictive for PS use cases. Furthermore, MCS being offered for PS over a commercial LTE network entails security vulnerabilities as the USIM is in the domain of the commercial network provider, thereby not satisfying minimum PSN security requirements. In this paper the use of the Trusted Execution Environment (TEE) as a hardware based secure element is evaluated. A solution developed for a Government entity in the Middle East is presented whereby any COTS smartphone connected to the internet, supporting TEE functionality with attestation to be taken over by a public safety officer securely.