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ETSI
TETRA
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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].

General structure of the TEA1 stream cipher. Note that all elements are bytes rather than bits. Click for further details.

General structure of the TEA2 stream cipher. Note that all elements are bytes rather than bits. Click for further details.

General structure of the TEA3 stream cipher. Note that all elements are bytes rather than bits. Click for further details.

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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