Improved Key Recovery Attacks on Reduced-Round AES with Practical Data and Memory Complexities

Determining the security of AES is a central problem in cryptanalysis, but progress in this area had been slow and only a handful of cryptanalytic techniques led to significant advancements. At Euro-crypt 2017 Grassi et al. presented a novel type of distinguisher for AES-like structures, but so far all the published attacks which were based on this distinguisher were inferior to previously known attacks in their complexity. In this paper we combine the technique of Grassi et al. with several other techniques to obtain the best known key recovery attack on 5-round AES in the single-key model, reducing its overall complexity from about 2(32) to about 2(22.5). Extending our techniques to 7-round AES, we obtain the best known attacks on AES-192 which use practical amounts of data and memory, breaking the record for such attacks which was obtained 18 years ago by the classical Square attack.