arXiv subjects

Robert Dumitru

Publications and source records attributed to Robert Dumitru.

6 recordsLinked to original sources

arXiv2025

Chypnosis: Undervolting-based Static Side-channel Attacks

Static side-channel analysis attacks, which rely on a stopped clock to extract sensitive information, pose a growing threat to embedded systems' security. To protect against such attacks, several proposed defenses aim to detect unexpected variations in the clock signal and clear sensitive states. In this work, we present \emph{Chypnosis}, an undervolting attack technique that indirectly stops the target circuit clock, while retaining stored data. Crucially, Chypnosis also blocks the state clearing stage of prior defenses, allowing recovery of secret information even in their presence. However, basic undervolting is not sufficient in the presence of voltage sensors designed to handle fault injection via voltage tampering. To overcome such defenses, we observe that rapidly dropping the supply voltage can disable the response mechanism of voltage sensor systems. We implement Chypnosis on various FPGAs, demonstrating the successful bypass of their sensors, both in the form of soft and hard IPs. To highlight the real-world applicability of Chypnosis, we show that the alert handler of the OpenTitan root-of-trust, responsible for providing hardware responses to threats, can be bypassed. Furthermore, we demonstrate that by combining Chypnosis with static side-channel analysis techniques, namely laser logic state imaging (LLSI) and impedance analysis (IA), we can extract sensitive information from a side-channel protected cryptographic module used in OpenTitan, even in the presence of established clock and voltage sensors. Finally, we propose and implement an improvement to an established FPGA-compatible clock detection countermeasure, and we validate its resilience against Chypnosis.

cs.CR↗

arXiv2025

Thunderhammer: Rowhammer Bitflips via PCIe and Thunderbolt (USB-C)

In recent years, Rowhammer has attracted significant attention from academia and industry alike. This technique, first published in 2014, flips bits in memory by repeatedly accessing neighbouring memory locations. Since its discovery, researchers have developed a substantial body of work exploiting Rowhammer and proposing countermeasures. These works demonstrate that Rowhammer can be mounted not only through native code, but also via remote code execution, such as JavaScript in browsers, and over networks. In this work, we uncover a previously unexplored Rowhammer vector. We present Thunderhammer, an attack that induces DRAM bitflips from malicious peripherals connected via PCIe or Thunderbolt (which tunnels PCIe). On modern DDR4 systems, we observe that triggering bitflips through PCIe requests requires precisely timed access patterns tailored to the target system. We design a custom device to reverse engineer critical architectural parameters that shape PCIe request scheduling, and to execute effective hammering access patterns. Leveraging this knowledge, we successfully demonstrate Rowhammer-induced bitflips in DDR4 memory modules via both PCIe slot connections and Thunderbolt ports tunnelling PCIe.

cs.CR↗

arXiv2024

On Borrowed Time -- Preventing Static Side-Channel Analysis

In recent years a new class of side-channel attacks has emerged. Instead of targeting device emissions during dynamic computation, adversaries now frequently exploit the leakage or response behaviour of integrated circuits in a static state. Members of this class include Static Power Side-Channel Analysis (SCA), Laser Logic State Imaging (LLSI) and Impedance Analysis (IA). Despite relying on different physical phenomena, they all enable the extraction of sensitive information from circuits in a static state with high accuracy and low noise -- a trait that poses a significant threat to many established side-channel countermeasures. In this work, we point out the shortcomings of existing solutions and derive a simple yet effective countermeasure. We observe that in order to realise their full potential, static side-channel attacks require the targeted data to remain unchanged for a certain amount of time. For some cryptographic secrets this happens naturally, for others it requires stopping the target circuit's clock. Our proposal, called Borrowed Time, hinders an attacker's ability to leverage such idle conditions, even if full control over the global clock signal is obtained. For that, by design, key-dependent data may only be present in unprotected temporary storage when strictly needed. Borrowed Time then continuously monitors the target circuit and upon detecting an idle state, securely wipes sensitive contents. We demonstrate the need for our countermeasure and its effectiveness by mounting practical static power SCA attacks against cryptographic systems on FPGAs, with and without Borrowed Time. In one case we attack a masked implementation and show that it is only protected with our countermeasure in place. Furthermore we demonstrate that secure on-demand wiping of sensitive data works as intended, affirming the theory that the technique also effectively hinders LLSI and IA.

cs.CR↗

arXiv2022

The Impostor Among US(B): Off-Path Injection Attacks on USB Communications

USB is the most prevalent peripheral interface in modern computer systems and its inherent insecurities make it an appealing attack vector. A well-known limitation of USB is that traffic is not encrypted. This allows on-path adversaries to trivially perform man-in-the-middle attacks. Off-path attacks that compromise the confidentiality of communications have also been shown to be possible. However, so far no off-path attacks that breach USB communications integrity have been demonstrated. In this work we show that the integrity of USB communications is not guaranteed even against off-path attackers.Specifically, we design and build malicious devices that, even when placed outside of the path between a victim device and the host, can inject data to that path. Using our developed injectors we can falsify the provenance of data input as interpreted by a host computer system. By injecting on behalf of trusted victim devices we can circumvent any software-based authorisation policy defences that computer systems employ against common USB attacks. We demonstrate two concrete attacks. The first injects keystrokes allowing an attacker to execute commands. The second demonstrates file-contents replacement including during system install from a USB disk. We test the attacks on 29 USB 2.0 and USB 3.x hubs and find 14 of them to be vulnerable.

cs.CR↗

arXiv2019

Information Dissemination Speed in Delay Tolerant Urban Vehicular Networks in a Hyperfractal Setting

This paper studies the fundamental communication properties of urban vehicle networks by exploiting the self-similarity and hierarchical organization of modern cities. We use an innovative model called "hyperfractal" that captures the self-similarities of both the traffic and vehicle locations but avoids the extremes of regularity and randomness. We use analytical tools to derive theoretical upper and lower bounds for the information propagation speed in an urban delay tolerant network (i.e., a network that is disconnected at all time, and thus uses a store-carry-and-forward routing model). We prove that the average broadcast time behaves as $n^{1-δ}$ times a slowly varying function, where $δ$ depends on the precise fractal dimension. Furthermore, we show that the broadcast speedup is due in part to an interesting self-similar phenomenon, that we denote as {\em information teleportation}. This phenomenon arises as a consequence of the topology of the vehicle traffic, and triggers an acceleration of the broadcast time. We show that our model fits real cities where open traffic data sets are available. We present simulations confirming the validity of the bounds in multiple realistic settings, including scenarios with variable speed, using both QualNet and a discrete-event simulator in Matlab.

cs.NI↗

arXiv2018

On Dividing a Rectangle

This paper deals with the history of the following problem: "Can an arbitrary rectangle be dissected into 3 non-rectangular congruent regions?" We present a new elementary proof that the answer is indeed no.

math.HO↗