Our work – with Jorge Blasco, Rikke Bjerg Jensen and Lenka Mareková – on the use of digital communication technologies in large-scale protests in Hong Kong was accepted at USENIX ’21. A pre-print is available on arXiv. Here’s the abstract:
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.
Our work can be seen in the tradition of “Can Johnny Build a Protocol? Co-ordinating developer and user intentions for privacy-enhanced secure messaging protocols” which documented the divergence of what higher-risk users – such as those in conflict with the authorities of a nation state – need and want and what secure messaging developers design for. This divergence is noteworthy because “human-rights activists” are a common point of reference in discussions around secure messaging.
However, our focus is not activists but participants in large-scale protests, i.e. our focus is more closely tied to specific needs in moments of heightened conflict, confrontation and mass mobilisation. In particular, we interviewed people who were in some shape or form involved in the Anti-ELAB protests in Hong Kong in 2019/2020. Several of our participants described themselves as “frontliners” which roughly means they were present in areas where direct confrontations with law enforcement took place.
As the title suggests our data speaks to how security needs and practices in this population are collective in nature: how decisions about security are made, what security features are deemed important, how people learn to understand security technologies. As an example take post-compromise security and forward secrecy:
, which I find very low (see Table 4 on page 19).
where 
is the targeted root hermit factor. Interpolating estimates from the BKZ 2.0 simulator and reflecting on the doubly exponential running time of BKZ in the blocksize 
we found: 
. However, since this might be controversial, we include estimates for both models.
. In theory these plots should all have slope 0.
for 
. As the name of the library indicates, it makes heavy use of the M4RI library both directly (i.e., by calling it) and indirectly (i.e., by using its concepts). We provide an open-source GPLv2+ C library for efficient linear algebra over 
to a series of matrix multiplications over 
. Furthermore, we propose a caching technique – Newton-John tables – to avoid finite field multiplications which is inspired by Kronrod’s method (“M4RM”) for matrix multiplication over 
. Using these two techniques we provide asymptotically fast triangular solving with matrices (TRSM) and PLE-based Gaussian elimination. As a result, we are able to significantly improve upon the state of the art in dense linear algebra over 
malb::blog 