trustlet

A trustlet is a small, isolated software module that runs inside a device’s trusted execution environment (TEE) and provides security-sensitive services to applications operating in the non-secure world. In TEEs based on technologies such as ARM TrustZone, the system separates hardware resources into a secure world and a non-secure world. The secure world hosts a trusted operating system and one or more trustlets, which are sometimes called trusted applications (TAs). These programs run with elevated privileges but are confined from other software and data in the non-secure world.

Trustlets implement security functions such as cryptographic operations, secure storage, attestation, key management, and sometimes digital rights management. They typically communicate with normal-world applications through defined interfaces provided by the TEE, using a standardized API set (for example, GlobalPlatform’s TEE Client API) or platform-specific calling conventions. Trustlets are loaded and executed by the TEE’s security kernel or a secure loader and are stored in protected memory regions to prevent tampering.

Lifecycle and provenance are important: trustlets are signed and provisioned by a trusted party, and the TEE enforces integrity and authenticity before loading them. They can be updated or revoked through secure provisioning processes, subject to platform policies.

Terminology varies by ecosystem. The term “trustlet” is widely used to describe these secure-world modules, while other platforms may refer to them as trusted applications (TAs). Regardless of naming, they serve as isolated, secure building blocks within the broader trusted execution environment.