In this document we describe the design of a multi-party messaging encryption protocol "Strongvelope". We hope that it will prove useful to people interested in understanding the inner workings of this protocol as well as cryptography and security experts to review the underlying concepts and assumptions.
In this design paper we are outlining the perspective of chat message protection through the Strongvelope module. This is different from the product (the Mega chat) and the transport means which it will be used with. Aspects of the chat product and transport are only referred to where appropriate, but are not subject to discussion in this document.
Secure communications are playing increasing roles in society, particularly in finance, journalism, and military projects. Current methods of securing e-mail and similar messaging methods rely on encryption of the message body, but the header with addressing information remains plaintext. This allows third party eavesdroppers to collect and analyse the header metadata and construct a network model of the participants in conversations (who, where, when, subject). In this article, we describe a method of communication where the header is also encrypted, hindering the assembly of the communicatio…
Instant messaging services are quickly becoming the most dominant form of communication among consumers around the world. Apple iMessage, for example, handles over 2 billion message each day, while WhatsApp claims 16 billion messages from 400 million international users. To protect user privacy, these services typically implement end-to-end and transport layer encryption, which are meant to make eavesdropping infeasible even for the service providers themselves. In this paper, however, we show that it is possible for an eavesdropper to learn information about user actions, the language of mess…
Recent years have seen a strong uptick in both the prevalence and real-world consequences of false information spread through online platforms. At the same time, encrypted messaging systems such as WhatsApp, Signal, and Telegram, are rapidly gaining popularity as users seek increased privacy in their digital lives. The challenge we address is how to combat the viral spread of misinformation without compromising privacy. Our FACTS system tracks user complaints on messages obliviously, only revealing the message's contents and originator once sufficiently many complaints have been lodged. Our sy…
This document is a technical overview and discussion of our work, a protocol for secure group messaging. By secure we mean for the actual users i.e. end-to-end security, as opposed to "secure" for irrelevant third parties. Our work provides everything needed to run a messaging session between real users on top of a real transport protocol. That is, we specify not just a key exchange, but when and how to run these relative to transport-layer events; how to achieve liveness properties such as reliability and consistency, that are time-sensitive and lie outside of the send-receive logic that cryp…
In recent years, it has come to attention that governments have been doing mass surveillance of personal communications without the consent of the citizens. As a consequence of these revelations, developers have begun releasing new protocols for end-to-end encrypted conversations, extending and making popular the old Off-the-Record protocol. Several new implementations of such end-to-end encrypted messaging protocols have appeared, and commonly used chat applications have been updated with these implementations as well. In this survey, we compare the existing implementations, where most of the…
Criminals are increasingly using mobile based communication applications, like WhatsApp, that have end-to-end encryption to connect to each other. This makes traditional analysis of call graphs, or traffic analysis, virtually impossible and so is a hindrance for law enforcement personnel. Old methods of traffic analysis have been rendered useless and criminals, including arms dealers and terrorists, are able to engage in criminal activity undetected by police. At present, law enforcement must use extensive manual effort to parse data provided by cell companies to extract information. We have b…
Cryptocat is a Free and Open Source Software (FL/OSS) browser extension that makes use of web technologies in order to provide easy to use, accessible, encrypted instant messaging to the general public. We aim to investigate how to best leverage the accessibility and portability offered by web technologies in order to allow encrypted instant messaging an opportunity to better permeate on a social level. We have found that encrypted communications, while in many cases technically well-implemented, suffer from a lack of usage due to their being unappealing and inaccessible to the "average end-us…
Messaging between two parties and in the group setting has enjoyed widespread attention both in practice, and, more recently, from the cryptographic community. One of the main challenges in the area is constructing secure (end-to-end encrypted) and efficient messaging protocols for group conversations. The popular messaging applications WhatsApp and Signal utilise a protocol in which, instead of sharing a single group key, members have individual \textit{sender keys}, which are shared with all other group members. The Sender Keys protocol is claimed to offer forward security guarantees. Howeve…
Herein this paper is presented a novel invention - called Dpush - that enables truly scalable spam resistant uncensorable automatically encrypted and inherently authenticated messaging; thus restoring our ability to exert our right to private communication, and thus a step forward in restoring an uncorrupted democracy. Using a novel combination of a distributed hash table[1] (DHT) and a proof of work[2] (POW), combined in a way that can only be called a synergy, the emergent property of a scalable and spam resistant unsolicited messaging protocol elegantly emerges. Notable is that the receiver…
Send and Pretend: Exploiting Transcript Consistency Issues in End-to-End Encrypted Group Chats
Interdisciplinary Transformation University (IT:U)（跨学科转型大学）；University of Vienna, Faculty of Computer Science（维也纳大学计算机科学学院）；SBA Research（SBA研究院）；UniVie Doctoral School Computer Science（维也纳大学计算机科学博士学院）；CDL AsTra（AsTra数字卓越中心）
MTProto 2.0 is a suite of cryptographic protocols for instant messaging at the core of the popular Telegram messenger application. In this paper we analyse MTProto 2.0 using the symbolic verifier ProVerif. We provide fully automated proofs of the soundness of MTProto 2.0's authentication, normal chat, end-to-end encrypted chat, and rekeying mechanisms with respect to several security properties, including authentication, integrity, secrecy and perfect forward secrecy; at the same time, we discover that the rekeying protocol is vulnerable to an unknown key-share (UKS) attack. We proceed in an i…
