{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T01:26:58Z","timestamp":1760232418878,"version":"build-2065373602"},"reference-count":23,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2022,11,3]],"date-time":"2022-11-03T00:00:00Z","timestamp":1667433600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Portuguese funding agency, FCT - Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia","award":["UIDB\/50014\/2020","2022.11929.BD","2020.04562.BD"],"award-info":[{"award-number":["UIDB\/50014\/2020","2022.11929.BD","2020.04562.BD"]}]},{"name":"Foundation for Science and Technology (FCT), Portugal","award":["UIDB\/50014\/2020","2022.11929.BD","2020.04562.BD"],"award-info":[{"award-number":["UIDB\/50014\/2020","2022.11929.BD","2020.04562.BD"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Photonics"],"abstract":"<jats:p>In this paper, we study the implementation of a secure key distribution system based on an ultra-long fiber laser with a bi-directional erbium-doped fiber amplifier. The resilience of the system was tested against passive attacks from an eavesdropper. A similarity was observed in the spectra for both secure configurations of the system and no signature that would allow an eavesdropper to obtain the secure state of the system was observed during the state transitions.<\/jats:p>","DOI":"10.3390\/photonics9110825","type":"journal-article","created":{"date-parts":[[2022,11,4]],"date-time":"2022-11-04T04:00:51Z","timestamp":1667534451000},"page":"825","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Resilience to Passive Attacks of a Secure Key Distribution System Based on an Ultra-Long Fiber Laser Using a Bi-Directional EDFA"],"prefix":"10.3390","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4864-9277","authenticated-orcid":false,"given":"Beatriz","family":"Soares","sequence":"first","affiliation":[{"name":"Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Rua do Campo Alegre, 687, 4150-179 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0384-1924","authenticated-orcid":false,"given":"Paulo","family":"Robalinho","sequence":"additional","affiliation":[{"name":"Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Rua do Campo Alegre, 687, 4150-179 Porto, Portugal"}]},{"given":"Ariel","family":"Guerreiro","sequence":"additional","affiliation":[{"name":"Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Rua do Campo Alegre, 687, 4150-179 Porto, Portugal"},{"name":"Faculdade de Ci\u00eancias, Universidade do Porto, Rua do Campo Alegre, 687, 4150-179 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7680-1056","authenticated-orcid":false,"given":"Orlando","family":"Fraz\u00e3o","sequence":"additional","affiliation":[{"name":"Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Rua do Campo Alegre, 687, 4150-179 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2022,11,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Stinson, D.R. 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