Tech project blog of Bastian Raschke

A5/1 cipher online simulator demo for visualisation of the internal algorithms

Written by Bastian Raschke.
Published 2016-09-11 in the category Security.

The A5/1 stream cipher has been used for a long time to encrypt communication data in the GSM system. The cipher was developed in 1987 and is finally broken since 2009. The cipher was initially kept secret but became public after reverse engineering. And the simluator we created, simulates/visualises every step of the algorithm.

We created the simulator for a project in the course “IT security for mobile systems” on the Trier University of Applied Sciences to understand how the A5/1 cipher exactly works. You can go over every step from the key initialization to the register initialization and finally to the cipherstream generation. The state change of the maj() function and of all 3 registers can be observed for each step. The used key is hardcoded in the file and can be changed of course.

A5/1 simulator demo
Screenshot of the A5/1 simulator

If you want to test the simulator by yourself, you can find it on this page.

The source code is available on Github:

A5/1 simulator on Github

Note: The simulator is just for general understanding and our implementation is probably not absolute correct!

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