Using a permissionless blockchain to build a smart door lock

Abstract

Door locks connected to the internet, also known as smart locks, offer more convenience and security to control access to a place if compared to conventional locks that use physical keys or with those that use keypads. For instance, smart locks are managed remotely and even if someone once had access permission at some point, they cannot copy the key to attempt unauthorized access later. Those benefits, however, might be compromised due to the centralized system architecture offered by locks’ vendors and manufacturers which allow users to control their devices - someone could gain access over the user’s device and data. This work explores how a permissionless blockchain – the public network of the Ethereum blockchain - can be leveraged to build a convenient and secure smart lock system, while giving the device owners full control over their devices by eliminating the central authority. It proposes an architecture and discusses in-depth the required components and other factors that must be taken into consideration while designing and implementing the system. Furthermore, a proof-of-concept application based on people that rent their places using hospitality services like Airbnb is implemented. The system allows hosts to remotely manage guests' permissions, delegate management rights to others, and allow guests to use a feature that blocks the owner’s permission to unlock the device during their stay. The proof-of-concept is evaluated regarding its functionalities, how long they take to be processed by the blockchain, and how much they cost to be executed. Among the findings are: (i) the proposed architecture and implementation were capable of delivering the expected behaviors for the smart lock functionalities; (ii) the delay associated with using the Ethereum blockchain are reasonable and fit the application use cases; (iii) besides the one-time-only operation to deploy the smart contract in the blockchain, the cost yielded for all other actions stayed below CAD 0.40, which is believed to be feasible considering the application context.