On Ends-to-Ends Encryption

Abstract

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. CCS CONCEPTS • Security and privacy → Security protocols; Cryptography; Formal methods and theory of security; Formal security models; Mobile and wireless security;

DiSCreet: Distributed Delivery Service with Context-Aware Cooperation

“…Thus, the removal of one member from the tree requires the participation of the closest neighbor to this member in the tree. The ART (Asynchronous Ratcheting Trees) protocol [15] enhances TGDH with the capability of creating a group in which all members but the group creator are not required to be online. In this protocol, the group creator can create the initial tree by using the X3DH key exchange algorithm [23] with ephemeral keys stored by each group member in a Public Key Infrastructure.…”

Supply Chain Cybersecurity and Small and Medium-Sized Enterprises (SMEs): Exploring Shortcomings in Third Party Risk Management of SMEs

“…The MLS standard is the product of an Internet Engineering Task Force (IETF) working group tasked with designing a protocol for secure group messaging [8]. MLS builds upon previous efforts in messaging security that have proven both effective and efficient [9,10]. Like many of these approaches, MLS maintains group keys in a binary tree as depicted in Figure 1 where individual members are represented by leaf nodes.…”

Design of an Efficient Distributed Delivery Service for Group Key Agreement Protocols

“…Thus, the removal of one member from the tree requires the participation of the closest neighbor to this member in the tree. The ART (Asynchronous Ratcheting Trees) protocol [12] enhances TGDH with the capability of creating a group in which all members but the group creator are not required to be online. In this protocol, the group creator can create the initial tree by using the X3DH key exchange algorithm [16] with ephemeral keys stored by each group member in a Public Key Infrastructure.…”