{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:14:34Z","timestamp":1760145274616,"version":"build-2065373602"},"reference-count":29,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2024,7,8]],"date-time":"2024-07-08T00:00:00Z","timestamp":1720396800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Italian Ministry of University and Research (MUR)","award":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"],"award-info":[{"award-number":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"]}]},{"name":"Italian Ministry of Health (MSAL)","award":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"],"award-info":[{"award-number":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"]}]},{"name":"Italian Ministry of Enterprises","award":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"],"award-info":[{"award-number":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"]}]},{"name":"LAIA lab (part of the SILA labs)","award":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"],"award-info":[{"award-number":["CUP H53D23003420006","CUP H23C22000860006","CUP H23C22000370006","CUP H73C22000880001","CUP H53C22000800006","CUP H53C22000650006","CUP B29J23000430005"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cryptography"],"abstract":"<jats:p>Denial of Service (DoS) attacks remain a persistent threat to online systems, necessitating continual innovation in defense mechanisms. In this work, we present an improved algorithm for mitigating DoS attacks through the augmentation of client puzzle protocols. Building upon the foundation of hashcash trees, a recently proposed data structure combining hashcash and Merkle trees, we introduce a new version of the data structure that enhances resistance against parallel computation (a common tactic employed by attackers). By incorporating the labels of children and the next node in a breadth-first traversal into the hash function, we establish a sequential processing order that inhibits parallel node evaluation. The added dependency on the next node significantly elevates the complexity of constructing hashcash trees, introducing a linear number of synchronization points and fortifying resilience against potential attacks. Empirical evaluation demonstrates the efficacy of our approach, showcasing its ability to accurately control puzzle difficulty while bolstering system security against DoS threats.<\/jats:p>","DOI":"10.3390\/cryptography8030030","type":"journal-article","created":{"date-parts":[[2024,7,8]],"date-time":"2024-07-08T11:30:02Z","timestamp":1720438202000},"page":"30","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Improve Parallel Resistance of Hashcash Tree"],"prefix":"10.3390","volume":"8","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2052-2063","authenticated-orcid":false,"given":"Mario","family":"Alviano","sequence":"first","affiliation":[{"name":"Department of Mathematics and Computer Science, University of Calabria, 87036 Rende, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-6136-9901","authenticated-orcid":false,"given":"Giada","family":"Gabriele","sequence":"additional","affiliation":[{"name":"Department of Mathematics and Computer Science, University of Calabria, 87036 Rende, Italy"}]}],"member":"1968","published-online":{"date-parts":[[2024,7,8]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1550147717741463","DOI":"10.1177\/1550147717741463","article-title":"A survey of distributed denial-of-service attack, prevention, and mitigation techniques","volume":"13","author":"Mahjabin","year":"2017","journal-title":"Int. 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