Tag Archives: anonymity

WireGuard is a Virtual Private Network (VPN), presented at NDSS 2017, recently integrated into the Linux Kernel and paid commercial VPNs such as NordVPN, Mullvad and ProtonVPN. It proposes a different approach from other classical VPN such as IPsec or OpenVPN because it does not let users configure cryptographic algorithms. The protocol inside WireGuard is a dedicated extension of IKpsk2 protocol from Noise Framework. Different analyses of WireGuard and IKpsk2 protocols have been proposed, in both the symbolic and the computational model, with or without computer-aided proof assistants. These analyses however consider different adversarial models or refer to incomplete versions of the protocols. In this work, we propose a unified formal model of WireGuard protocol in the symbolic model. Our model uses the automatic cryptographic protocol verifiers Sapic+, ProVerif and Tamarin. We consider a complete protocol execution, including cookie messages used for resistance against denial of service attacks. We model…

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The Anti-Extradition Law Amendment Bill protests in Hong Kong present a rich context for exploring information security practices among protesters due to their large-scale urban setting and highly digitalised nature. We conducted in-depth, semi-structured interviews with 11 participants of these protests. Research findings reveal how protesters favoured Telegram and relied on its security for internal communication and organisation of on-the-ground collective action; were organised in small private groups and large public groups to enable collective action; adopted tactics and technologies that enable pseudonymity; and developed a variety of strategies to detect compromises and to achieve forms of forward secrecy and post-compromise security when group members were (presumed) arrested. We further show how group administrators had assumed the roles of leaders in these ‘leaderless’ protests and were critical to collective protest efforts.

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End-to-end encryption (E2EE) in messaging platforms enable people to securely and privately communicate with one another. Its widespread adoption has however raised concerns that illegal content might now be shared undetected. Following the global pushback against key escrow systems, client-side scanning based on perceptual hashing has been recently proposed by governments and researchers to detect illegal content in E2EE communications. 

Last week, Apple announced that it will use client-side scanning to detect child sexual abuse material in iCloud photos, users’ personal photo libraries. The announcement has triggered concerns among experts about the trade-off achieved by client-side scanning mechanisms and the risk of them being misused. 

In this talk, we will present what is to the best of our knowledge the first framework to evaluate the robustness of perceptual hashing-based client-side scanning which we proposed two months ago. We will present a general black-box attack against any perceptual hashing algorithm and two white-box attacks for discrete cosine-based algorithms. Using these, we will show in a large-scale evaluation that more than 99.9% of images can be successfully attacked in a black-box setting while preserving the content of the image. We will then show our attack to generate diverse perturbations, suggesting that straightforward mitigation strategies would be ineffective. Taken together, our results raise concerns on the robustness of perceptual hashing-based client-side scanning mechanisms to black-box adversarial machine learning attacks.

This talk is based on “Adversarial Detection Avoidance Attacks: Evaluating the robustness of perceptual hashing-based client-side scanning” by Shubham Jain*, Ana-Maria Cretu*, Yves-Alexandre de Montjoye and available as preprint here: https://arxiv.org/abs/2106.09820.

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