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IFT Research Call

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October 2024

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On decentralized secure channel setup using Ethereum accounts

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Ramses Fernandez

Vac – Applied Cryptography & ZK

Institute of Free Technology

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IFT Research Call

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October 2024

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Structure

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This presentation is divided into the following parts:

  1. Reminder of MLS and treeKEM.
  2. The use of smart contracts for group management.
  3. The login protocol.
  4. Future research.

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IFT Research Call

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October 2024

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Main results

We introduce a protocol which combines:

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  1. The use of smart contracts for group management.
  2. The MLS protocol allows users to keep track of the state of the group locally.
  3. A decentralized authentication protocol with session management, which uses Ethereum addresses as identifiers.

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IFT Research Call

Institute of Free Technology – Vac

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October 2024

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Motivation

The usual approach to group messaging is based on a ratcheting scheme called Sender Keys.

Sender Keys offers good security properties, and is a great solution for 1 – to – 1 communications but it is not that efficient in group communications

This is where MLS comes into play, offering an efficient and well established mechanism for setting a common group key which can be used for communications in group of thousands of users.

The main problem in our setting is that MLS is not decentralized by design. And that’s the main motivation of this research: we present an architecture which makes use of smart contracts for the management of groups, with the view on a decentralized communication protocol.

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IFT Research Call

Institute of Free Technology – Vac

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October 2024

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Sender Keys

Sender Keys is the backbone of WhatsApp, Signal, and others.

Its main components are:

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  1. A secure communication channel between peers.
  2. A symmetric encryption mechanism.
  3. A digital signature scheme.
  4. A central server providing total ordering to some messages.

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IFT Research Call

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October 2024

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Basics on the MLS protocol…

The MLS protocol is designed to facilitate efficient and secure messaging within groups ranging from just a couple of users to potentially thousands. It brings:

1. Flexible implementation.

2. Forward secrecy.

3. Post-compromise security.

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IFT Research Call

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October 2024

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… and treeKEM

It is the underlying mechanism for the MLS protocol.

It works as a combination of recursive hashing and a final KDF step.

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IFT Research Call

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October 2024

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Confusing concepts

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Forward secrecy ensures the confidentiality of past messages in the event of a key exposure.

Post-compromise security ensures that security can be restored after a key exposure.

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IFT Research Call

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October 2024

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MLS

The main drawbacks of the MLS protocol for our interests are:

  1. It is federated by design.
  2. It requires total ordering in application and control messages. This is obtained via an (untrusted) central server.

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IFT Research Call

Institute of Free Technology – Vac

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October 2024

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The smart contract approach

The way we plan to increase the decentralization level is creating a smart contract in charge of managing the state of a group.

In this first stage, since MLS has tools for group authentication, the smart contract will only store an Access Control List (ACL).

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IFT Research Call

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October 2024

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Login Protocol

One of the main differences between our decentralized version of the MLS and solutions currently available will be the inclusion of a modular decentralized login protocol.

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This protocol will include session management, and will be controlled by a separate smart contract.

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This

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IFT Research Call

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October 2024

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Basic architecture

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October 2024

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Basic architecture (user connection)

Below follows the connection between users:

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IFT Research Call

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October 2024

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Comparison with other solutions

Currently, most of the existing messaging applications:

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  1. Have good scalability at the price of centralization.
  2. Have good scalability and decentralization features at the price of weak authentication.

Our deMLS project aims at providing:

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  1. High decentralization.
  2. High scalability.
  3. Strong authentication.
  4. Forward secrecy and post-compromise security.

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IFT Research Call

Institute of Free Technology – Vac

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October 2024

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Future work

Next steps in this project include:

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  1. Using a single smart contract in charge of managing all groups.
  2. Increasing the privacy level in groups, so the users belonging to a group remain secret to third parties.
  3. Improve the login protocol to make it fully modular and comprehensive with better security properties.
  4. Deploy the protocol in testnet, and perform an analysis in terms of complexity, security, efficiency and gas cost.

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IFT Research Call

Institute of Free Technology – Vac

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October 2024

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Questions?

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IFT Research Call

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October 2024

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IFT Research Call

Institute of Free Technology – Vac

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October 2024