Paper 2021/554

Grover on Caesar and Vigenère Ciphers

Gyeongju Song and Kyungbae Jang and Hyunji Kim and Wai-Kong Lee and Hwajeong Seo

Abstract

Quantum computers can solve or accelerate specific problems that were not possible with classical computers. Grover's search algorithm, a representative quantum algorithm, finds a specific solution from $N$ unsorted data with $O(\sqrt{N})$ queries. This quantum algorithm can be used to recover the key of symmetric cryptography. In this paper, we present a practical quantum attack using Grover's search to recover the key of ciphers ({\tt Caesar} and {\tt Vigenère}). The proposed quantum attack is simulated with quantum programming tools (ProjectQ and Qiskit) provided by IBM. Finally, we minimize the use of quantum resources and recover the key with a high probability.