Abstract Trusted execution environments (TEEs) have emerged as a key technology in the cybersecurity domain. A TEE provides an isolated environment in which sensitive computations can be executed securely. Trusted applications running in TEEs are developed using standardized APIs that many hardware platforms for TEE adhere to. However, formal models tailored to standard TEE APIs are not well developed. In this paper, we present a formal specification of TEE APIs using Maude. We focus on Trusted Storage API and Cryptographic Operations API, which are foundational to mobile and IoT applications. The effectiveness of our approach is demonstrated through formal analysis of MQT-TZ, an open-source TEE application for IoT. Our formal analysis has revealed security vulnerabilities in the implementation of MQT-TZ, and we patch and confirm its integrity using model checking.