# Practical, Low-Cost Fault Injection Attacks on Personal Smart Devices
## 1 Introduction  
Fault injection attacks (FIA) are physical interventions that exploit the circuit's direct implementation [1]. In contrast to exploitation of software vulnerabilities, FIA attacks usually require the attacker to have physical access to the victim's device. Because of that, countermeasures are often considered for application in specific fields that are required to operate in a challenging environment such as space and automotive, and for specific low-power high-performance applications [2, 3]. While fault attacks are known to be much more effective than software-only attacks in their ability to corrupt a device's ordinary execution flow [4], setting up an environment for injecting transient faults is a complex process, which includes the usage of expensive equipment such as oscilloscopes, XYZ stages, high-end pulse generators and amplifiers [5, 6, 7]. Defense from these attacks was therefore considered out of scope for many devices that are not expected to be subjected to such intensive physical intervention. In this work we argue that fault attack countermeasures need to be deployed in more settings. We demonstrate a novel method for performing fault attacks outside the lab. Our key motivating factor is the existence of a large and unregulated market for hardware field-replaceable units (FRUs). Examples of devices that incorporate FRUs include interface cards in routers, touch screens and sensor assemblies in mobile phones, ink cartridges in printers, batteries in health sensors, and so on. As noted by [PERSON] et al. [8], third-party FRU installations often use cheap components of unknown pedigree, and thus may introduce, knowingly or unknowingly, counterfeit or malicious components into otherwise securedevices. [PERSON] et al. divided attacks based on malicious FRUs into two different classes: **first-order attacks**, in which the malicious FRU falsifies interactions with the device in the ways a standard user would, but without the user's consent, and **second-order attacks**, which go beyond exchanging properly formed data, and attempt to cause a malfunction in the device driver and compromise the operating system kernel. Our work considers a new form of **third-order attacks**, which do not rely on data exchange between the FRU and the device at all, but instead exploit its physical proximity to launch fault injection attacks. Specifically, in this paper we make the following contributions:  
1. We propose a new attack model for fault attacks, in which the adversary triggers a fault on the device under test (DUT) using a malicious FRU. 2. We design and build an EM fault injection device based on inexpensive components, and show how this injection device can disrupt the normal course of execution of a processor commonly used in smart devices. 3. We present a proof-of-concept attack, in which a fault generated by our injection device leaks confidential information from a high-privileged service in the device under test. Specifically, we show how to extract a private key used by a privileged signing service running in Linux, using the default PyCrypto library, by combining our fault injection method with attack code running with regular user permissions. 4. We discuss various countermeasures which can be used against our attack, and present a software-only approach which is capable of reliably stopping our proof-of-concept attack. This software-based countermeasure was submitted to the authors of the PyCrypto library. Our chosen attack model offers a unique combination of challenges and advantages. First, we note that our attacker device must be small and inexpensive enough to be mass-produced, and power-efficient enough to run on the limited power provided to the FRU by the host device. Second, we cannot apply any sample preparation steps to the device under test (DUT) such as thinning, flipping or decapsulation. In terms of advantages, we note that the FRU is placed in very close proximity to the device under test, often inside the case and its associated EM shielding.