Citation: Hsueh, C.-W.; Chin, C.-T. Toward Trusted IoT by General Proof-of-Work. Sensors 2022, 23, 15. https://doi.org/10.3390/s23010015 Academic Editor: Dawid Polap Received: 25 October 2022 Revised: 4 December 2022 Accepted: 15 December 2022 Published: 20 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sensors Article Toward Trusted IoT by General Proof-of-Work Chih-Wen Hsueh 1, * and Chi-Ting Chin 2 1 Department of Computer Science and Information Engineering, National Taiwan University, Taipei 10617, Taiwan 2 Department of Risk Management and Insurance, Ming Chuan University, Taipei 11103, Taiwan * Correspondence: cwhsueh@csie.ntu.edu.tw; Tel.: +886-928-777-371 Abstract: Internet of Things (IoT) is used to describe devices with sensors that connect and exchange data with other devices or systems on the Internet or other communication networks. Actually, the data not only represent the concrete things connected but also describe the abstract matters related. Therefore, it is expected to support trust on IoT since blockchain was invented so that trusted IoT could be possible or, recently, even metaverse could be imaginable. However, IoT systems are usually composed of a lot of device nodes with limited computing power. The built-in unsolved performance and energy-consumption problems in blockchain become more critical in IoT. The other problems such as finality, privacy, or scalability introduce even more complexity so that trusted IoT is still far from realization, let alone the metaverse. With general Proof of Work (GPoW), the energy consumption of Bitcoin can be reduced to less than 1 billionth and proof of PowerTimestamp (PoPT) can be constructed so that a global even ordering can be reached to conduct synchronization on distributed systems in real-time. Therefore, trusted IoT is possible. We reintroduce GPoW with more mathematic proofs so that PoPT can be optimal and describe how PoPT can be realized with simulation results, mining examples and synchronization scenario toward trusted IoT. Keywords: IoT; blockchain; finality; consensus; PoW; PoPT; PowerTimestamp; synchronization; energy; metaverse 1. Introduction Since the invention of the vending machine in the 1980s, the Internet of Things (IoT) has been a concept to bring computers, networks, and machines to improve our daily life. Many hardware, software and networking technologies such as Radio Frequency IDentification (RFID), Near Field Communication (NFC), Wireless Sensor Network, Cloud computing, Edge computing, etc. [1,2] are emerged, forming various IoT platforms, and successfully reach different goals, such as the smart home. Basically, IoT is used to describe devices (mostly embedded systems) with sensors that connect and exchange data with other devices or systems on the Internet or other communication networks. Actually, the data not only represent the concrete things such as temperature or time at the devices connected but also describes the abstract matters related such as security or privacy. Therefore, it is expected to support trust on IoT since blockchain was invented so that trusted IoT could be possible. As a trust machine, blockchain needs to support trust in all aspects such as security, privacy, transparency, efficiency, justice, etc. As Augmented Reality, Virtual Reality, and Mixed Reality become more mature, people even imagine and develop platforms and applications for the metaverse recently. Beyond IoT, which integrates computers with real world, metaverse goes to the virtual universe created in computers. Trusted IoT is the key component to connect the real world and virtual “universe” to realize all the applications. Otherwise, metaverse is just an augmented game. However, IoT systems are usually composed of a lot of device nodes with limited com- puting power. The built-in and unsolved performance and energy-consumption problems in blockchain become more critical in IoT. The other problems such as finality, privacy, or Sensors 2022, 23, 15. https://doi.org/10.3390/s23010015 https://www.mdpi.com/journal/sensors