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Quantum Comput."],"published-print":{"date-parts":[[2025,6,30]]},"abstract":"<jats:p>Here we introduce an improved approach to Variational Quantum Attack Algorithms (VQAA) on crytographic protocols. Our methods provide robust quantum attacks to well-known cryptographic algorithms, more efficiently and with remarkably fewer qubits than previous approaches. We implement simulations of our attacks for symmetric-key protocols such as S-DES, S-AES, and Blowfish. For instance, we show how our attack allows a classical simulation of a small 8-qubit quantum computer to find the secret key of one 32-bit Blowfish instance with 24 times fewer number of iterations than a brute-force attack. Our work also shows improvements in attack success rates for lightweight ciphers such as S-DES and S-AES. Further applications beyond symmetric-key cryptography are also discussed, including asymmetric-key protocols and hash functions. In addition, we also comment on potential future improvements of our methods. Our results bring one step closer assessing the vulnerability of large-size classical cryptographic protocols with Noisy Intermediate-Scale Quantum (NISQ) devices, and set the stage for future research in quantum cybersecurity.<\/jats:p>","DOI":"10.1145\/3718349","type":"journal-article","created":{"date-parts":[[2025,2,18]],"date-time":"2025-02-18T10:13:06Z","timestamp":1739873586000},"page":"1-24","update-policy":"https:\/\/doi.org\/10.1145\/crossmark-policy","source":"Crossref","is-referenced-by-count":4,"title":["Hacking Cryptographic Protocols with Advanced Variational Quantum Attacks"],"prefix":"10.1145","volume":"6","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-7510-1192","authenticated-orcid":false,"given":"Borja","family":"Aizpurua","sequence":"first","affiliation":[{"name":"Research, Multiverse Computing, San Sebasti\u00e1n, Spain and Basic Sciences, Universidad de Navarra Tecnun Escuela de Ingenier\u00eda, San Sebastian, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7467-4951","authenticated-orcid":false,"given":"Pablo","family":"Bermejo","sequence":"additional","affiliation":[{"name":"Donostia International Physics Center, San Sebastian, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7058-8426","authenticated-orcid":false,"given":"Josu","family":"Etxezarreta Mart\u00ednez","sequence":"additional","affiliation":[{"name":"Basic Sciences, Universidad de Navarra Tecnun Escuela de Ingenier\u00eda, San Sebastian, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4496-8115","authenticated-orcid":false,"given":"Rom\u00e1n","family":"Or\u00fas","sequence":"additional","affiliation":[{"name":"Research, Multiverse Computing, San Sebasti\u00e1n, Spain, Donostia International Physics Center, San Sebastian, Spain, and Ikerbasque Foundation for Science, Bilbao, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"320","published-online":{"date-parts":[[2025,3,12]]},"reference":[{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.adhoc.2015.01.006"},{"key":"e_1_3_2_3_2","article-title":"Assessing the benefits and risks of quantum computers","author":"Scholten Travis L.","year":"2024","unstructured":"Travis L. 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