{"licence":{"name":"CC BY-SA 4.0","spdx":"CC-BY-SA-4.0","url":"https://creativecommons.org/licenses/by-sa/4.0/","attribution":"Atlas, a bilingual technical dictionary (https://cmaintz.github.io/tech-atlas/)"},"id":"security/non-repudiation","url":{"en":"https://cmaintz.github.io/tech-atlas/en/terms/security/non-repudiation/","da":"https://cmaintz.github.io/tech-atlas/da/terms/security/non-repudiation/"},"term":{"en":"Non-repudiation","da":"Uafviselighed (non-repudiation)"},"aka":{"en":[],"da":["ikke-benægtelse"]},"domain":["security"],"cluster":"fundamentals","layer":"data","status":"current","era":1989,"summary":{"en":"Proof of who did something that is strong enough that they cannot later deny having done it.","da":"Så stærkt bevis for, hvem der gjorde noget, at vedkommende ikke senere kan nægte at have gjort det."},"body":{"formal":{"en":"The assurance that the sender of a message gets proof of delivery and the receiver gets proof of who sent it, so neither can later deny their part. It usually rests on digital signatures, which only the holder of a private key could have made.","da":"Sikkerheden for, at afsenderen af en besked får bevis for levering, og modtageren får bevis for, hvem der sendte den, så ingen af dem senere kan benægte deres del. Den bygger typisk på digitale signaturer, som kun indehaveren af en privat nøgle kan have lavet."},"plain":{"en":"Like signing for a parcel in front of a witness - you cannot later claim it never came, and the courier cannot claim to have left it with you if they did not.","da":"Som at kvittere for en pakke med et vidne til stede - du kan ikke senere påstå, at den aldrig kom, og budet kan ikke påstå at have afleveret den, hvis det ikke skete."},"inPractice":{"en":"A supplier signs a contract with a Danish region using a digital signature; when it later disputes the agreed price, the region can show that only the supplier's own key could have produced that signature.","da":"En leverandør skriver under på en kontrakt med en region med en digital signatur; da leverandøren senere sætter spørgsmål ved den aftalte pris, kan regionen vise, at kun leverandørens egen nøgle kan have lavet signaturen."},"whyItMatters":{"en":"Contracts, payments and audit records are only worth something if people cannot simply say “that was not me” afterwards.","da":"Kontrakter, betalinger og revisionsspor er kun noget værd, hvis folk ikke bare kan sige “det var ikke mig” bagefter."}},"deepDive":{"en":"Non-repudiation is a technical property built on asymmetric cryptography and, crucially, on the surrounding trust and evidence infrastructure. A digital signature is produced by hashing the message (with a collision-resistant function such as SHA-256) and signing that hash with the signer's private key under a signature scheme such as RSA-PSS, ECDSA or EdDSA; a verifier recomputes the hash and checks it against the signature using the signer's public key. Because only the holder of the private key could have produced a signature that verifies, and because any change to the message breaks the hash match, the scheme binds a specific identity to specific content and simultaneously proves integrity. This is distinct from a Message Authentication Code (HMAC): a MAC uses a shared symmetric key, so either party could have generated it and neither can prove to a third party which one did - a MAC gives authentication but not non-repudiation.\n\nThe cryptography alone is not sufficient in law or in disputes. Non-repudiation depends on binding the key to a real-world identity, usually through a public-key infrastructure (PKI) where a certificate authority vouches for the mapping in an X.509 certificate, and on trusted timestamping (RFC 3161) so that a signature can be shown to have existed before the certificate was revoked or expired. It also depends on the signer's exclusive control of the private key; if the key is stored insecurely or shared, the \"you cannot deny it\" claim collapses, which is why key protection in hardware (smart cards, HSMs, secure elements) matters. Long-term validation formats such as PAdES, XAdES and CAdES embed revocation data and timestamps precisely so a signature remains verifiable years later.\n\nIn the EU the legal weight is set by the eIDAS Regulation (EU) No 910/2014. Article 25(1) forbids denying an electronic signature legal effect merely because it is electronic, while Article 25(2) gives a qualified electronic signature (QES) - one created with a qualified signature-creation device and based on a qualified certificate - legal effect equivalent to a handwritten signature, recognised across all Member States. In Denmark, qualified signatures are issued by qualified trust service providers, with the public NemLog-in signing service a common route. eIDAS was substantially amended in 2024 (eIDAS 2.0), introducing the European Digital Identity Wallet, though Article 25's core signature provisions remain.\n\nA frequent misconception is that any electronic signature, such as a scanned image or a typed name, provides non-repudiation; without cryptographic binding and identity assurance it provides almost none. Another is conflating non-repudiation of origin (proof of who signed) with non-repudiation of receipt or delivery (proof that a party received a message), which needs a separate mechanism such as a signed acknowledgement or a trusted delivery service. Non-repudiation builds on authentication and integrity but goes further: authentication convinces the relying party at the time, whereas non-repudiation must convince a neutral third party, such as a court, after the fact.","da":"Uafviselighed er en teknisk egenskab, der bygger på asymmetrisk kryptografi og - helt afgørende - på den omkringliggende tillids- og bevisinfrastruktur. En digital signatur dannes ved at hashe beskeden (med en kollisionsresistent funktion som SHA-256) og signere den hash med underskriverens private nøgle under et signaturskema som RSA-PSS, ECDSA eller EdDSA; en verifikator genberegner hashen og kontrollerer den mod signaturen med underskriverens offentlige nøgle. Fordi kun indehaveren af den private nøgle kan have lavet en signatur, der verificerer, og fordi enhver ændring af beskeden bryder hash-sammenligningen, binder ordningen en bestemt identitet til et bestemt indhold og beviser samtidig integritet. Det adskiller sig fra en Message Authentication Code (HMAC): en MAC bruger en delt symmetrisk nøgle, så begge parter kan have dannet den, og ingen kan bevise over for en tredjepart hvem - en MAC giver autentificering, men ikke uafviselighed.\n\nKryptografien alene er ikke tilstrækkelig juridisk eller i tvister. Uafviselighed afhænger af at binde nøglen til en virkelig identitet, typisk gennem en public-key-infrastruktur (PKI), hvor en certifikatmyndighed indestår for koblingen i et X.509-certifikat, og af betroet tidsstempling (RFC 3161), så en signatur kan vises at have eksisteret, før certifikatet blev spærret eller udløb. Den afhænger også af, at underskriveren har enekontrol over den private nøgle; hvis nøglen opbevares usikkert eller deles, falder påstanden om, at \"du ikke kan nægte det\", sammen - derfor er nøglebeskyttelse i hardware (smartkort, HSM'er, secure elements) vigtig. Langtidsvaliderende formater som PAdES, XAdES og CAdES indlejrer netop spærredata og tidsstempler, så en signatur forbliver verificerbar mange år senere.\n\nI EU fastlægges den juridiske vægt af eIDAS-forordningen (EU) nr. 910/2014. Artikel 25, stk. 1, forbyder at nægte en elektronisk signatur retsvirkning alene, fordi den er elektronisk, mens artikel 25, stk. 2, giver en kvalificeret elektronisk signatur (QES) - dannet med en kvalificeret signaturfremstillingsenhed og baseret på et kvalificeret certifikat - retsvirkning svarende til en håndskreven underskrift, anerkendt i alle medlemsstater. I Danmark udstedes kvalificerede signaturer af kvalificerede tillidstjenesteudbydere, hvor den offentlige NemLog-in-signeringstjeneste er en almindelig vej. Bemærk, at eIDAS blev væsentligt ændret i 2024 (\"eIDAS 2.0\"-forordningen), som indfører den europæiske digitale identitetstegnebog (EU Digital Identity Wallet), selv om kernebestemmelserne om signaturer i artikel 25 består.\n\nEn hyppig misforståelse er, at enhver elektronisk signatur, fx et scannet billede eller et indtastet navn, giver uafviselighed; uden kryptografisk binding og identitetssikring giver den næsten ingen, og dens bevisværdi er svag. En anden er at sammenblande uafviselighed af oprindelse (bevis for hvem der signerede) med uafviselighed af modtagelse eller levering (bevis for, at en part modtog en besked), som kræver en separat mekanisme som en signeret kvittering eller en betroet leveringstjeneste. Uafviselighed bygger på autentificering og integritet, men går videre: autentificering overbeviser den part, der forlader sig på den, i selve øjeblikket, mens uafviselighed skal overbevise en neutral tredjepart, fx en domstol, bagefter."},"edges":[{"type":"requires","to":"cs/authentication","confidence":"high","strength":"normal"},{"type":"requires","to":"security/integrity","confidence":"high","strength":"normal"},{"type":"requires","to":"cs/public-key-cryptography","confidence":"high","strength":"normal"}],"depth":3,"sources":[{"title":"NIST Glossary - Non-repudiation","url":"https://csrc.nist.gov/glossary/term/non_repudiation","tier":"standard","publisher":"NIST"},{"title":"ISO/IEC 27000:2018 - Information security management systems, Overview and vocabulary","tier":"standard","publisher":"ISO/IEC"},{"title":"Regulation (EU) No 910/2014 (eIDAS) - Article 25, Legal effects of electronic signatures","url":"https://eur-lex.europa.eu/eli/reg/2014/910/oj/eng","tier":"standard","publisher":"EUR-Lex"}],"draft":true}