Lock Picking in the Era of Internet of Things Edward Knight, Sam Lord, and Budi Arief School of Computing, University of Kent, United Kingdom [email protected], [email protected], [email protected] Abstract—Smart locks are a recent development in the mechanism to allow their user to unlock it should the Internet of Things that aim to modernise traditional key- associated smartphone become unavailable (e.g. due to the based padlock systems. They allow users to operate the smartphone being lost or stolen, or if the smartphone’s lock with their smartphone instead of carrying around a physical key. Typically, smart locks have a cloud system for battery has run out). In a sense, these override mechanisms sharing access with other people, which makes them ideal provide a way to open the lock with “something the user for schemes such as communal lockers or bike sharing. One knows”, akin to a combination lock or a password. of the smart locks available on the market is that produced by Master Lock. They are an established brand, and unlike Locks have traditionally been judged on their physical many of the single product companies that have provided security; how well they stand up to picking, shimming and insecure offerings, Master Lock have so far shown that cutting into. Smart locks need to be physically secure as their locks are reasonably secure and resistant to known attacks such as shimming, fuzzing, and replay attacks. This well as have a secure connection to a secure management paper provides a security analysis of the Master Lock system. The market of smart locks is mostly made up of Bluetooth padlock. More importantly, it reveals that there small startup companies manufacturing a single product, were several security vulnerabilities, including a serious one and many of them have been proven to be insecure (for ex- in the Application Programming Interface used by Master ample [6] and [7]). The work presented in this paper looks Lock to provide a crucial feature for managing access. We carried out a responsible disclosure exercise to Master Lock, at the security of a smart lock built by an established lock but communication proved to be quite a challenge. In the end manufacturer (Master Lock, https://www.masterlock.com/) we managed to establish contact, and as a result the most to see if they have better security than other (relatively serious vulnerabilities have now been patched. This indicates new) companies. that responsible disclosure is a valuable exercise, but we still need better report-and-response mechanisms. The key contributions of this paper are: (i) a thorough Keywords: security, IoT, smart locks, API vulnerabilities, and systematic security analysis of the Master Lock Blue- responsible disclosure. tooth padlock, leading to (ii) the revelation of several vulnerabilities, including a serious security issue with the I.I NTRODUCTION Application Programming Interface (API) used, and (iii) Internet of Things (IoT) devices are gaining popularity an impactful responsible disclosure exercise, which ended and becoming more ubiquitous in our lives. There has up with the manufacturer of Master Lock patching their been a significant growth of IoT devices over the past system to address the vulnerabilities we uncovered. few years [1], but this new market has gained a reputation Section II provides an overview of related work in investi- for churning out insecure systems. This has led to security gating security issues in smart locks. Section III introduces and privacy concerns (such as [2]–[4]) and even a large- the Master Lock Bluetooth padlock, including its system scale Distributed Denial of Service attack using the Mirai and communication architecture. Section IV outlines our botnet of compromised IoT devices [5]. methodology for finding potential security vulnerabilities Smart locks provide a modern alternative to the traditional in Master Lock, along with an attacker model. Section V key or combination lock, and access is generally managed presents and discusses the results of our investigation, as by an online service. Typically the locks themselves do well as our responsible disclosure. Section VI concludes not connect to the internet directly, but communicate our paper and provides some ideas for future work. with a smartphone app, which in turn talks to the online service. This separation allows for locks to work offline, II.R ELATED WORK an important feature if the owner is without an internet Limited prior research has been undertaken regarding the connection or the online service becomes unavailable, security of smart locks. Nevertheless, there is a wide range but also increases the attack space. The smartphone can of potential attack vectors. These include physical attack, be thought of as the “key”, allowing its user to lock, wireless communication sniffing and spoofing, as well as unlock and even share the smart lock with other users. exploiting the supporting back end services that enable Furthermore, these locks typically provide an override many of the “smart” features of smart locks. There is a wealth of related work in IoT security, some of which has informed our research here. An early paper by Suo et al. [8] provides an overview of four key layers of typical IoT architecture (perceptual, network, support and application layers). Of particular interest to us is the support layer, in which centralised control func- tionality (such as access management) is implemented. Figure 1. Master Lock and its override buttons The challenge here is how to detect malicious activity, such as commands that should not be executed due to insufficient privileges, but may be performed anyway due Bluetooth LE REST API to improperly implemented access control. Figure 2. Master Lock components and their communication Wurm et al. [9] performed security analyses on consumer and industrial IoT devices. Some of the techniques used • Man-in-the-Middle: by hosting a service which sits (hardware and network communication analysis, reverse between the phone and the real cloud service, it is engineering) gave us some initial direction when looking possible to modify requests and responses at Master Lock’s offering. • Reading the firmware: downloading the firmware for We found that most of the investigation into breaking the device from the cloud service and looking for any smart lock security has come from hacking communities, hard-coded secrets with scarce academic papers looking into the potential Additionally, after mapping out the API, the author made security vulnerabilities of smart locks. One example of a Software Development Kit (SDK) for accessing the the latter is a paper on the Noke¯ smart lock [10]. The API. This SDK made it easier for them to investigate the researchers focused on the manual override feature of the methods provided by the API and to search for potential Noke¯ lock and studied human-generated unlock codes. vulnerabilities. They showed that the human-generated codes were of low enough entropy to pose a serious vulnerability. A Master Lock have registered patents for the lock itself [11], mechanical brute-force tool was built to demonstrate this. managing the authentication keys over wireless communi- cation [12] and for wireless firmware updates [13]. This A DEF CON presentation on hacking Bluetooth locks [6] indicated to us that Master Lock has put some effort into specifically stated that two locks (from Noke¯ and Master designing these systems, and also gave us a starting point Lock) had not been cracked, showing that neither padlock for areas to investigate. had trivially broken security. This provided a challenge and a list of common attacks on smart locks to focus on: III.S YSTEM OF INTEREST:MASTER LOCK • Plain-text passwords: Bluetooth transmission of pass- We chose to focus on Master Lock as it is an established words without encryption brand specialising in various lock and padlock systems. • Replay attacks: where a recording of the communi- We had hoped that this industry experience would result cation can be replayed to unlock the device in a more secure system than their competitors. • Fuzzing: sending invalid data can cause the device to enter an error state and open A. System architecture • Device spoofing: using a computer to pretend to be The Master Lock Bluetooth padlock is a Bluetooth enabled the lock, we can listen to commands sent by a phone padlock which comes in two form factors for indoor and and use them to unlock the real device outdoor usage. It has the look and feel of an ordinary • Hard-coded secrets: some lock manufacturers include padlock but instead of a keyway, it has a 4-directional pad hard-coded secrets in the smartphone application, that serves as the input device for the override mechanism which can be retrieved by decompiling it (see Figure 1). Another presentation from DEF CON included the full The overall Master Lock system has three key components methodology used to hack an August Smart Lock installed (Figure 2): the padlock, the smartphone application, and in a front door [7]. This was of particular interest since the the cloud service. These components communicate to each methods used attacked both the Bluetooth communication other by using two protocols: Bluetooth Low Energy layer and the supporting cloud service, which is similar in (BLE) and HTTP, using the smartphone application as the architecture to the Master Lock service. They looked at: interlinking component. • Investigating the cloud service API: checking if users The padlock has the Slave Role, and communicates with can get privileged data or perform privileged actions the smartphone, which gets the Master Role [14, Vol 6, from a guest account Part B, Section 1.1, p. 2553]. This means that the padlock advertises itself when it turns on, on one of the three To share the device with other users, one can either share a advertising channels.