CryptoDB
Jens Alich
Publications
Year
Venue
Title
2025
TOSC
Observations on TETRA Encryption Algorithm TEA-3
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.
Coauthors
- Jens Alich (1)
- Amund Askeland (1)
- Subhadeep Banik (1)
- Tim Beyne (1)
- Anne Canteaut (1)
- Patrick Felke (1)
- Gregor Leander (1)
- Willi Meier (1)
- Lukas Stennes (1)