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ETSI
TETRA
TEA
    
TAA
TETRA Authentication Algorithm

TAA or TAA1, the abbreviation of TETRA Authentication Algorithm 1, is a suite of 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]. They are used for authentication, key derivation and Over The Air Re-keying (OTAR) [3].

The suite consists of cryptographic primitives and non-cryptographic transformation functions. All cryptographic primitives rely on a proprietary block cipher known as HURDLE, which was developed in 1996/97 at Royal Holloway University of London (UK) for ETSI-SAGE. After evaluation by the other ETSI-SAGE members, it was submitted as a formal ETSI standard.


Structure
All TETRA-related algorithms are secret and have never been submitted for peer-review or in-depth security analysis. 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]. A slightly less critical flaw was found in the TAA algorithm, which leads to a weak anonymization [2][3].

HURDLE is a balanced 16-round Feistel network with a 128-bit key and a 64-bit block size. Each round key — 96 bits are used per round — is derived from its predecessor, through a simple linear function that wraps around in 16 rounds. For a more complete description, check out [3].

 Read the paper
 More about TETRA:BURST


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

    Paper submitted to Crypto Museum. 9 August 2023.

  2. Full source code of TAA1, TEA1, TEA2 and TEA3 algorithms in C
    Reverse-engineered and used for analysis and real life tests.
    Midnight Blue, 9 August 2023.
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.
Further information
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Crypto Museum. Created: Wednesday 09 August 2023. Last changed: Saturday, 12 August 2023 - 13:57 CET.
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