Towards Provably Secure Internet Communication


This project started in 2017 and has been successfully completed.


Marta Mularczyk (ETH)
Ueli Maurer (ETH)


Nowadays, the wide-spread access to the Internet enables quick communication, unrestrained by physical location. However, this comes at a cost of new security risks, since now private messages become available to adversarial entities, located anywhere around the world. Hence, cryptographic protocols that add security to the communication become essential.

Since different situations have different functional and security requirements, the number of secure-communication protocols with different security-functionality-efficiency trade-offs is rapidly growing. For example, we have various session-establishment protocols (such as TCP-based TLS, or Google’s QUIC based on faster but less reliable UDP), various secure-messaging protocols (such as Signal’s double ratchet, or the group messaging protocol currently being standardized by the MLS working group), and many more. The large number of use cases, trade-offs and accompanying protocols (often designed in an ad-hoc fashion and without clearly specified security guarantees) motivates the goal of this project, which is to explore from the cryptographic perspective the space of secure-communication protocols.

More specifically, for various functionality requirements, we specify different security guarantees, where usually stronger guarantees require less efficient protocols. This is done with the help of cryptographic modeling tools, such as the (standard) game-based security analysis and the constructive cryptography framework (which, in particular, allows to express the strong guarantee of composability, i.e. a protocol is secure even if arbitrary other protocols are executed simultaneously). This allows to, first, express the exact guarantees of existing protocols (and either verify that they meet their intuitive goals, or discover a gap between the intuition and reality) and, second, provide new protocols offering previously unexplored trade-offs.


Efficient Ratcheting: Almost-Optimal Guarantees for Secure Messaging
Daniel Jost and Ueli Maurer and Marta Mularczyk
Advances in Cryptology – EUROCRYPT 2019, pp. 159-188, Springer, 2019

A Unified and Composable Take on Ratcheting
Daniel Jost and Ueli Maurer and Marta Mularczyk
Theory of Cryptography Conference, TCC, 2019

Continuous Group Key Agreement with Active Security
Joël Alwen, Sandro Coretti, Daniel Jost, and Marta Mularczyk
Theory of Cryptography Conference, TCC, 2020

On the Insider Security of MLS
Joël Alwen and Daniel Jost and Marta Mularczyk
Theory of Cryptography Conference, TCC, 2020