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Plausible deniability in cryptography allows users to deny their participation in a particular communication or the contents of their messages, thereby ensuring privacy. Popular end-to-end encrypted messaging apps employ the Signal protocol, which incorporates message deniability. However, their current user interfaces only allow access to the blunt tool of message deletion. Denying a message requires users to claim that the counterpart in their conversation has the technical sophistication to forge a message when no usable message forgery tools are available. We evaluate a step towards bridging this gap in the form of a new transcript-editing feature implemented within the Signal app which allows each user to maintain an independent, locally-editable transcript of their conversation. We gave users hands-on experience with this app in the context of resolving a social dispute, and measured their ability to understand its implications both technically and ethically. Users find our interface intuitive and can reason about deniability, but are divided by which circumstances for which deniability is appropriate or desirable. We recommend users be given transparent access to choose when their conversations are deniable versus non-repudiable, instead of the status quo of somewhere-in-between. Our study introduces a novel approach by providing hands-on experience and evaluating its usability. This method offers insights into practical deniability implementation and lays the groundwork for future research. 

Typing on a midair keyboard in mixed reality can be difficult due to the lack of tactile feedback when virtual keys are tapped. Locating the keyboard over a real-world surface offers a potential way to mitigate this issue. We measured user performance and preference when a virtual keyboard was located on a table, on a wall, or in midair. Despite the additional tactile feedback offered by the table and wall locations, we found the midair location had a significantly higher entry rate with a similar error rate compared to the other locations. Participants also preferred the midair location over the other locations. 

Abstract Filming atomic motion within molecules is an active pursuit of molecular physics and quantum chemistry. A promising method is laser-induced Coulomb Explosion Imaging (CEI) where a laser pulse rapidly ionizes many electrons from a molecule, causing the remaining ions to undergo Coulomb repulsion. The ion momenta are used to reconstruct the molecular geometry which is tracked over time (i.e., filmed) by ionizing at an adjustable delay with respect to the start of interatomic motion. Results are distorted, however, by ultrafast motion during the ionizing pulse. We studied this effect in water and filmed the rapid “slingshot” motion that enhances ionization and distorts CEI results. Our investigation uncovered both the geometry and mechanism of the enhancement which may inform CEI experiments in many other polyatomic molecules. 

Two-Factor Authentication (2FA) hardens an organization against user account compromise, but adds an extra step to organizations’ mission-critical tasks. We investigate to what extent quantitative analysis of operational logs of 2FA systems both supports and challenges recent results from user studies and surveys identifying usability challenges in 2FA systems. Using tens of millions of logs and records kept at two public universities, we quantify the at-scale impact on organizations and their employees during a mandatory 2FA implementation. We show the multiplicative effects of device remembrance, fragmented login services, and authentication timeouts on user burden. We find that user burden does not deviate far from other compliance and risk management time requirements already common to large organizations. We investigate the cause of more than one in twenty 2FA ceremonies being aborted or failing, and the variance in user experience across users. We hope our analysis will empower more organizations to protect themselves with 2FA. 

Abstract Protein aggregation results in an array of different size soluble oligomers and larger insoluble fibrils. Insoluble fibrils were originally thought to cause neuronal cell deaths in neurodegenerative diseases due to their prevalence in tissue samples and disease models. Despite recent studies demonstrating the toxicity associated with soluble oligomers, many therapeutic strategies still focus on fibrils or consider all types of aggregates as one group. Oligomers and fibrils require different modeling and therapeutic strategies, targeting the toxic species is crucial for successful study and therapeutic development. Here, we review the role of different‐size aggregates in disease, and how factors contributing to aggregation (mutations, metals, post‐translational modifications, and lipid interactions) may promote oligomers opposed to fibrils. We review two different computational modeling strategies (molecular dynamics and kinetic modeling) and how they are used to model both oligomers and fibrils. Finally, we outline the current therapeutic strategies targeting aggregating proteins and their strengths and weaknesses for targeting oligomers versus fibrils. Altogether, we aim to highlight the importance of distinguishing the difference between oligomers and fibrils and determining which species is toxic when modeling and creating therapeutics for protein aggregation in disease. 

Abstract An ability to promote therapeutic immune cells to recognize cancer cells is important for the success of cell‐based cancer immunotherapy. We present a synthetic method for functionalizing the surface of natural killer (NK) cells with a supramolecular aptamer‐based polyvalent antibody mimic (PAM). The PAM is synthesized on the cell surface through nucleic acid assembly and hybridization. The data show that PAM has superiority over its monovalent counterpart in powering NKs to bind to cancer cells, and that PAM‐engineered NK cells exhibit the capability of killing cancer cells more effectively. Notably, aptamers can, in principle, be discovered against any cell receptors; moreover, the aptamers can be replaced by any other ligands when developing a PAM. Thus, this work has successfully demonstrated a technology platform for promoting interactions between immune and cancer cells.