Side-Channel Attacks on the Yubikey 2 One-Time Password Generator

Abstract

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.

Information Leaks Without Memory Disclosures

“…This is due to the fact that they require measurements that can only be done if the attacker has physical access to the machine. These include power [24,28,32], electromagnetic (EM) emanation [30], and acoustical [17,42] analyses, where the attacker needs to measure the power consumed, the EM field produced, or the sound produced by the device, respectively. In all cases, the instructions executed often have a distinct power, EM, or sound measurement.…”

Sweet Dreams and Nightmares: Security in the Internet of Things

“…We demonstrate in [ORP13] that SCA attacks are a relevant threat for the tokens: A non-invasive side-channel analysis exploiting the EM emanations of the AES implementation requires approximately 500 EM measurements to recover the full key. Given approximately one hour of access to a Yubikey 2, an adversary can impersonate the legitimate owner and generate valid one-time passwords, even after the token has been returned.…”

Formal verification of the YubiKey and YubiHSM APIs in Maude-NPA

“…An independent analysis was given by blogger Fredrik Björck in 2009 [6,7], raising issues that Yubico responded to in a subsequent post. Oswald, Richter, et al [21] analyze the YubiKey, generation 2, for side-channel attacks. They show that noninvasive measurements of the power consumption of the device allow retrieving the AES-key within approximately one hour of access.…”