Observations on TETRA Encryption Algorithm TEA-3

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.

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Publication Details

Journal
IACR Transactions on Symmetric Cryptology
Published
2025-03-07
DOI
https://doi.org/10.46586/tosc.v2025.i1.276-308
Citations
1
Primary Topic
Nuclear Physics and Applications
Type
article
Field-Weighted Citation Impact
1.88

Funders

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article

Observations on TETRA Encryption Algorithm TEA-3

Lukas Stennes, Subhadeep Banik, Tim Beyne, Amund Askeland et al.
1 citations
IACR Transactions on Symmetric Cryptology
Nuclear Physics and Applications
1.88
article

Observations on TETRA Encryption Algorithm TEA-3

Lukas Stennes, Subhadeep Banik, Tim Beyne, Amund Askeland, Anne Canteaut, Patrick Felke, Gregor Leander, Willi Meier, Jens Alich
article en
1 citations

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.

IACR Transactions on Symmetric CryptologyVol. 2025(1)
Institut national de recherche en sciences et technologies du numérique (FR), FHNW University of Applied Sciences and Arts Northwestern Switzerland (CH), University of Applied Sciences Emden Leer (DE), University of Bergen (NO), Università della Svizzera italiana (CH), Ruhr University Bochum (DE), KU Leuven (BE)
Deutsche Forschungsgemeinschaft
Openalex Percentile: Top 20%
Nuclear Physics and Applications
1.88
DOIOpen Access PDFOpenAlex
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Observations on TETRA Encryption Algorithm TEA-3 — Lukas Stennes, Subhadeep Banik, et al. · IACR Transactions on Symmetric Cryptology (2025) | TGRS Research Map | TGRS