This document presents the requirements for validating the “Decentralized PKI for IoT Systems” functionality, which ensures secure communication between resource-constrained devices like IoTs (constrained systems). Therefore, a decentralized PKI is implemented, which does not rely on a Certification Authority for its operation but instead relies on a blockchain to ensure data integrity. To guarantee secure communication between IoT devices, the NSL (Needham-Schroeder-Lowe) protocol is used to generate session keys from information stored on the blockchain. The selected system has been placed in a realistic scenario where IoT devices securely communicate via the MQTT protocol, utilizing a TLS layer configured for the use of pre-shared keys through a cryptographic protocol that leverages authenticated public keys via a blockchain system based on Algorand. The “Decentralized PKI for IoT Systems” functionality has been validated in an IoT Laboratory setup by RSE that monitors electrical loads.