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ETSI
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TEA
TETRA Encryption Algorithm

TEA, short for TETRA Encryption Algorithm, 1 is a suite of encryption algorithms, associated with Terrestrial Trunked Radio (TETRA), a European standard for public safety and emergency services, standardized by the European Telecommunications Standards Institute (ETSI) [1]. There are four flavours, TEA1 to TEA4, only one of which is optionally present in each TETRA radio device:

The TEA algorithms are used for the encryption of voice and data traffic on a TETRA radio net­work. Each TEA is a stream cipher and uses an 80-bit key, although the key of TEA1 is internally reduced to 32 bits. In addition, the TETRA Authentication Algorithm (TAA) is used for authenti­cation, key derivation and OTAR. The TAA and TEA algorithms are secret and have never been submitted for peer-review or in-depth security analysis.

  1. Not to be confused with Tiny Encryption Algorithm.  Wikipedia

Reverse-engineering
In July 2023, Dutch cyber security firm Midnight Blue revealed that it had managed to extract, isolate, reconstruct and analyse the TAA, TEA1, TEA2 and TEA3 algorithms from a working TETRA radio as part of its RE:TETRA and TETRA:BURST research projects. Five vulnerabilities were found, two of which were deemed critical [2]. The project allows us to take a closer look at the ciphers.

The diagrams below show the structures of the known TEA1, TEA2 and TEA3 stream ciphers, each of which takes an 80-bit key. They are shown here without further comments, so that they can be compared more easily. For a detailed description, click the relevant diagram or read [3].




References
  1. Wikipedia, Terrestrial Trunked Radio
    Visited 27 July 2023.

  2. TETRA:BURST
    Midnight Blue, 24 July 2023.
     More

  3. Carlo Meijer, Wouter Bokslag and Jos Wetzels,
    All cops are broadcasting: TETRA under scrutiny

    Paper submitted to Crypto Museum. 9 August 2023.
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Crypto Museum. Created: Wednesday 09 August 2023. Last changed: Saturday, 12 August 2023 - 14:16 CET.
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