Cihangir Tezcan
Middle East Technical University, Turkey

Gregor Leander
Ruhr University Bochum, Germany

Keywords: KASUMI · A5/3 · SPECK · TEA3 · cryptanalysis · GPU

Abstract

Key lengths in symmetric cryptography are determined with respect to the brute force attacks with current technology. While nowadays at least 128-bit keys are recommended, there are many standards and real-world applications that use shorter keys. In order to estimate the actual threat imposed by using those short keys, precise estimates for attacks are crucial. In this work we provide optimized implementations of several widely used algorithms on GPUs, leading to interesting insights on the cost of brute force attacks on several real-word applications. In particular, we optimize KASUMI (used in GPRS/GSM), SPECK (used in RFID communication), and TEA3 (used in TETRA). Our best optimizations allow us to try 2^35.72, 2^36.72, and 2^34.71 keys per second on a single RTX 4090 GPU. Those results improve upon previous results significantly, e.g. our KASUMI implementation is more than 15 times faster than the optimizations given in the CRYPTO'24 paper (Avoine et al.) improving the main results of that paper by the same factor. With these optimizations, in order to break GPRS/GSM, RFID, and TETRA communications in a year, one needs around 11, 22 billion, and 1.36 million RTX 4090 GPUs, respectively. For KASUMI, the time-memory trade-off attacks of Avoine et al. can be performed with 142 RTX 4090 GPUs instead of 2400 RTX 3090 GPUs or, when the same amount of GPUs are used, their table creation time can be reduced to 20.6 days from 348 days, crucial improvements for real world cryptanalytic tasks.