## Cryptology ePrint Archive: Report 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.

Category / Keywords: implementation / Quantum Computers, Grover's Search Algorithm, Caesar Cipher, Vigenère Cipher

Date: received 26 Apr 2021, last revised 18 Jun 2021

Contact author: hwajeong84 at gmail com, thdrudwn98 at gmail com, starj1023 at gmail com, khj1594012 at gmail com, waikonglee at gachon ac kr

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2021/554

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