TY - JOUR AU - Hicks, Christopher AU - Garcia, Flavio D. AU - Oswald, David PY - 2018/05/08 Y2 - 2024/03/29 TI - Dismantling the AUT64 Automotive Cipher JF - IACR Transactions on Cryptographic Hardware and Embedded Systems JA - TCHES VL - 2018 IS - 2 SE - Articles DO - 10.13154/tches.v2018.i2.46-69 UR - https://tches.iacr.org/index.php/TCHES/article/view/874 SP - 46-69 AB - <p>AUT64 is a 64-bit automotive block cipher with a 120-bit secret key used in a number of security sensitive applications such as vehicle immobilization and remote keyless entry systems. In this paper, we present for the first time full details of AUT64 including a complete specification and analysis of the block cipher, the associated authentication protocol, and its implementation in a widely-used vehicle immobiliser system that we have reverse engineered. Secondly, we reveal a number of cryptographic weaknesses in the block cipher design. Finally, we study the concrete use of AUT64 in a real immobiliser system, and pinpoint severe weaknesses in the key diversification scheme employed by the vehicle manufacturer. We present two key-recovery attacks based on the cryptographic weaknesses that, combined with the implementation flaws, break both the 8 and 24 round configurations of AUT64. Our attack on eight rounds requires only 512 plaintext-ciphertext pairs and, in the worst case, just 2<sup>37.3</sup> offline encryptions. In most cases, the attack can be executed within milliseconds on a standard laptop. Our attack on 24 rounds requires 2 plaintext-ciphertext pairs and 2<sup>48.3</sup> encryptions to recover the 120-bit secret key in the worst case. We have strong indications that a large part of the key is kept constant across vehicles, which would enable an attack using a single communication with the transponder and negligible offline computation.</p> ER -