On Ends-to-Ends Encryption: Asynchronous Group Messaging with Strong Security Guarantees

In the past few years secure messaging has become mainstream, with over a billion active users of end-to-end encryption protocols through apps such as WhatsApp, Signal, Facebook Messenger, Google Allo, Wire and many more. While these users\u27 two-party communications now enjoy very strong security guarantees, it turns out that many of these apps provide, without notifying the users, a weaker property for group messaging: an adversary who compromises a single group member can intercept communications indefinitely. One reason for this discrepancy in security guarantees is that most existing group messaging protocols are fundamentally synchronous, and thus cannot be used in the asynchronous world of mobile communications. In this paper we show that this is not necessary, presenting a design for a tree-based group key exchange protocol in which no two parties ever need to be online at the same time, which we call Asynchronous Ratcheting Tree (ART). ART achieves strong security guarantees, in particular including post-compromise security. We give a computational security proof for ART\u27s core design as well as a proof-of-concept implementation, showing that ART scales efficiently even to large groups. Our results show that strong security guarantees for group messaging are achievable even in the modern, asynchronous setting, without resorting to using inefficient point-to-point communications for large groups. By building on standard and well-studied constructions, our hope is that many existing solutions can be applied while still respecting the practical constraints of mobile devices

A multi-layer extension of the stochastic heat equation

Motivated by recent developments on solvable directed polymer models, we define a 'multi-layer' extension of the stochastic heat equation involving non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio

Oceans without history? Marine Cultural Heritage and the sustainable development agenda

This paper aims to set out the role Marine Cultural Heritage (MCH) can play in informing responses to global challenges and enhancing the sustainable development of coastal zones. This requires recognition of the importance of MCH as a knowledge base amongst marine ocean scientists, policy makers and marine stakeholders on the one hand and a greater effort by marine heritage specialists to engage with the 2030 Agenda on the other. The forthcoming UN Decade of Ocean Science for Sustainable Development (2021–2030) provides an opportunity to engage with the sea more widely but it is argued that the cultural element provided by considering past human action is currently lacking. The importance of understanding human interaction with the sea in terms of gaining a more complete picture of human history is briefly presented and a definition of MCH as all past action in the human zone is given. The article then sets out how MCH can enhance sustainable development in the marine zone with particular reference to SDG14 considering heritage tourism, coastal development and infrastructure, development aid policy, climate change, coastal management, fisheries and the offshore industry. The article highlights that the knowledge and data from MCH should be seen as crucial in evidence-based decision making across the coastal and marine sectors. The paper concludes that the inclusion of MCH approaches in initiatives aiming at coastal and ocean sustainability is not just advisable—it is essentia

Both “illness and temptation of the enemy”: melancholy, the medieval patient and the writings of King Duarte of Portugal (r. 1433–38)

Recent historians have rehabilitated King Duarte of Portugal, previously maligned and neglected, as an astute ruler and philosopher. There is still a tendency, however, to view Duarte as a depressive or a hypochondriac, due to his own description of his melancholy in his advice book, the Loyal Counselor. This paper reassesses Duarte's writings, drawing on key approaches in the history of medicine, such as narrative medicine and the history of the patient. It is important to take Duarte's views on his condition seriously, placing them in the medical and theological contexts of his time and avoiding modern retrospective diagnosis. Duarte's writings can be used to explore the impact of plague, doubt and death on the life of a well-educated and conscientious late-medieval ruler

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Class, Youth and Dirty Jobs: The Working-Class and Post-War Britain in Pete Townshend's Quadrophenia

FOS

On Ends-to-Ends Encryption: Asynchronous Group Messaging with Strong Security Guarantees

In the past few years secure messaging has become mainstream, with over a billion active users of end-to-end encryption protocols such as Signal. The Signal Protocol provides a strong property called post-compromise security to its users. However, it turns out that many of its implementations provide, without notification, a weaker property for group messaging: an adversary who compromises a single group member can read and inject messages indefinitely. We show for the first time that post-compromise security can be achieved in realistic, asynchronous group messaging systems. We present a design called Asynchronous Ratcheting Trees (ART), which uses tree-based Diffie-Hellman key exchange to allow a group of users to derive a shared symmetric key even if no two are ever online at the same time. ART scales to groups containing thousands of members, while still providing provable security guarantees. It has seen significant interest from industry, and forms the basis for two draft IETF RFCs and a chartered working group. Our results show that strong security guarantees for group messaging are practically achievable in a modern setting