Attribute-Based Authentication in Secure Group Messaging for Distributed Environments and Safer Online Spaces

TL;DR

This paper introduces an attribute-based authentication method for secure group messaging that enhances privacy and security, using attribute credentials instead of digital certificates, with formal security proofs and efficient implementation.

Contribution

It proposes a novel attribute-authenticated CGKA scheme, AA-CGKA, with formal security proofs and practical performance comparable to certificate-based solutions.

Findings

AA-CGKA achieves requirement integrity, unforgeability, and unlinkability.

The implementation demonstrates performance similar to traditional certificate-based methods.

The scheme enhances privacy by avoiding digital certificates and linking attacks.

Abstract

The Messaging Layer security (MLS) and its underlying Continuous Group Key Agreement (CGKA) protocol allows a group of users to share a cryptographic secret in a dynamic manner, such that the secret is modified in member insertions and deletions. Although this flexibility makes MLS ideal for implementations in distributed environments, a number of issues need to be overcome. Particularly, the use of digital certificates for authentication in a group goes against the group members' privacy. In this work we provide an alternative method of authentication in which the solicitors, instead of revealing their identity, only need to prove possession of certain attributes, dynamically defined by the group, to become a member. Instead of digital certificates, we employ Attribute-Based Credentials accompanied with Selective Disclosure in order to reveal the minimum required amount of information and to prevent attackers from linking the activity of a user through multiple groups. We formally define a CGKA variant named Attribute-Authenticated Continuous Group Key Agreement (AA-CGKA) and provide security proofs for its properties of Requirement Integrity, Unforgeability and Unlinkability. We also provide an implementation of our AA-CGKA scheme and show that it achieves performance similar to a trivial certificate-based solution.