The widespread embedding of electronic devices into the daily-life objects, and their integration in the so called Internet of the Things (IoT), has raised a number of challenges for the design of Systems-on-Chip (SoCs) devices. Tiny manufacturing costs, stringent security, and ultra-low power operation constraints have considerably raised SoC design requirements. More than incremental approaches which try to re-use current cryptographic mechanisms, the new generation of IoT devices will require novel solutions which deeply integrate their hardware-intrinsic features to program execution. This paper proposes a low-cost PUF-based authentication architecture aiming to secure code execution in IoT SoCs. The solution is deeply embedded into the processor micro-architecture, so as to minimize re-design costs and performance penalties. This new architecture model not only deals with the most common threats against code and data authenticity and integrity, but also provides an approach to extract from processor’s caches a stable and unpredictable key that is used in the code and data authentication process.