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We describe how Pearson’s χ2-test can be used as a natural complement to Welch’s t-test for black box leakage detection. In particular, we show that by using these two tests in combination, we can mitigate some of the limitations due to the moment-based nature of existing detection techniques based on Welch’s t-test (e.g., for the evaluation of higher-order masked implementations with insufficient noise). We also show that Pearson’s χ2-test is naturally suited to analyze threshold implementations with information lying in multiple statistical moments, and can be easily extended to a distinguisher for key recovery attacks. As a result, we believe the proposed test and methodology are interesting complementary ingredients of the side-channel evaluation toolbox, for black box leakage detection and non-profiled attacks, and as a preliminary before more demanding advanced analyses.

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Often overlooked, microcontrollers are the central component in embedded systems which drive the evolution toward the Internet of Things (IoT). They are small, easy to handle, low cost, and with myriads of pervasive applications.An increasing number of microcontroller-equipped systems are security and safety critical. In this tutorial, we take a critical look at the security aspects of today's microcontrollers. We demonstrate why the implementation of sensitive applications on a standard microcontroller can lead to severe security problems. To this end, we summarize various threats to microcontroller-based systems, including side-channel analysis and different methods for extracting embedded code. In two case studies, we demonstrate the relevance of these techniques in real-world applications: Both analyzed systems, a widely used digital locking system and the YubiKey 2 onetime password generator, turned out to be susceptible to attacks against the actual implementations, allowing an adversary to extract the cryptographic keys which, in turn, leads to a total collapse of the system security.

Abstract. The classical way of authentication with a username-password pair is often insufficient: an adversary can choose from a multitude of methods to obtain the credentials, e.g., by guessing passwords using a dictionary, by eavesdropping on network traffic, or by installing malware on the system of the target user. To overcome this problem, numerous solutions incorporating a second factor in the authentication process have been proposed. A particularly wide-spread approach provides each user with a hardware token that generates a One-Time Password (OTP) in addition to the traditional credentials. The token itself comprises a secret cryptographic key that, together with timestamps and counters, is used to derive a fresh OTP for each authentication. A relatively new yet widespread example for an OTP token is the Yubikey 2 produced by Yubico. This device employs an open-source protocol based on the mathematically secure AES and emulates a USB keyboard to enter the OTP in a platform-independent manner. In this paper, we analyse the susceptibility of the Yubikey 2 to side-channel attacks. We show that by noninvasively measuring the power consumption and the electro-magnetic emanation of the device, an adversary is able to extract the full 128-bit AES key with approximately one hour of access to the Yubikey 2. The attack leaves no physical traces on the device and can be performed using low-cost equipment. In consequence, an adversary is able to generate valid OTPs, even after the Yubikey 2 has been returned to the owner.