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Observations on TETRA Encryption Algorithm TEA-3
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| Abstract: | We present a number of observations on TEA-3, a stream cipher used in TETRA radio networks that was kept secret until recently. While the same also holds for the six other TETRA encryption algorithms, we pick TEA-3 to start with, as (i) it is not obviously weakened as TEA-{1,4,7} but (ii) in contrast to TEA-2 it is approved for extra-European emergency service, and (iii) as already noted by [MBW23] the TEA-3 design surprisingly contains a non-bijective S-box. Most importantly, we show that the 80-bit non-linear feedback shift register operating on the key decomposes into a cascade of two 40-bit registers. Although this hints at an intentional weakness at first glance, we are not able to lift our results to a practical attack. Other than that, we show how the balanced non-linear feedback functions used in the state register of TEA-3 can be constructed. |
BibTeX
@article{tosc-2025-35395,
title={Observations on TETRA Encryption Algorithm TEA-3},
journal={IACR Transactions on Symmetric Cryptology},
publisher={Ruhr-Universität Bochum},
volume={2025},
pages={276-308},
url={https://tosc.iacr.org/index.php/ToSC/article/view/12077},
doi={10.46586/tosc.v2025.i1.276-308},
author={Jens Alich and Amund Askeland and Subhadeep Banik and Tim Beyne and Anne Canteaut and Patrick Felke and Gregor Leander and Willi Meier and Lukas Stennes},
year=2025
}