Overview

This repository contains the implementation of the Authentication Steps protocol. It extends the official Java implementation for the Signal application to provide a more complete post-compromise security property against active Man-in-the-Middle attackers.

Tests

Several tests are performed, which vary according to:

• the number of authentication steps;
• the presence of out-of-order or dropped messages;
• the presence of an attacker.

There are several types of out-of-order messages. The type denoted as simple describes any message dropped or out-of-order, even messages during authentication steps. They can arrive in any possible order, but messages sent before an authentication step never arrive after it. This is in contrast to late messages, which are out-of-order messages that can arrive even after an authentication step arrives.

We also capture two types of attackers: replace and inject. Attacker replace leaks the state of one party. When the party sends the next message, the attacker drops the message and replaces the ciphertext with a forged ciphertext, encrypting a different plaintext message. On the other hand, attacker inject leaks the state of one party at the end of an epoch, and adds a new message at the end of the epoch.

Test name	Authentication steps	Out-of-order	Attacker
testNoAdvOneAuth	1	Simple	None
testReplaceOneAuth	1	Simple	Replace
testInjectOneAuth	1	Simple	Inject
testNoAdvTwoAuth	2	Simple	None
testReplaceTwoAuth	2	Simple	Replace
testInjectTwoAuth	2	Simple	Inject
testManyEpochs	150	None	None
testInjectAcrossAuth	2	Late	Inject

Different types of attacker

Branches

• testing the original implementation can be done on branch test0;
• the implementation without late messages management can be found on branch test1;
• the full implementation can be found on branch test2;
• the master branch contains additionnaly the test with out-of-band checks.

Running the tests

To run the tests, go to the branch you want to test and run the command:

./ gradlew clean test -- tests TestName

Tests results

The following table lists the results of those tests:

Benchmarking

To launch benchmarking tests, use:

./ gradlew clean test -- tests BenchmarkingTest

Then graphs can be drawn using the graph.py file.