{"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":"cs/public-key-infrastructure","url":{"en":"https://cmaintz.github.io/tech-atlas/en/terms/cs/public-key-infrastructure/","da":"https://cmaintz.github.io/tech-atlas/da/terms/cs/public-key-infrastructure/"},"term":{"en":"Public key infrastructure (PKI)","da":"Offentlig nøgleinfrastruktur (PKI)"},"aka":{"en":[],"da":[]},"domain":["cs"],"cluster":"cryptography","layer":"theory","status":"current","era":1988,"summary":{"en":"The system of trusted issuers, rules and records that hands out digital certificates and says which ones to believe.","da":"Systemet af betroede udstedere, regler og registre, der udsteder digitale certifikater og afgør, hvilke man kan stole på."},"body":{"formal":{"en":"The set of certificate authorities, policies, software and procedures that issue, sign, store and cancel digital certificates, forming chains of trust from a few root keys down to each website, device or person.","da":"Samlingen af certifikatudstedere, politikker, software og procedurer, der udsteder, signerer, gemmer og tilbagekalder digitale certifikater og danner tillidskæder fra nogle få rodnøgler ned til hvert websted, hver enhed eller person."},"plain":{"en":"Like the passport system - a few governments everyone trusts issue passports, border guards know what a real one looks like, and lost ones are reported as no longer valid.","da":"Som passystemet - nogle få stater, som alle stoler på, udsteder pas, grænsevagter ved, hvordan et ægte pas ser ud, og bortkomne pas meldes ugyldige."},"inPractice":{"en":"A region runs its own PKI so every hospital laptop gets a certificate; the hospital wifi and VPN let in only laptops whose certificate the region issued and has not cancelled.","da":"En region driver sin egen PKI, så hver bærbar på hospitalerne får et certifikat; hospitalets wifi og VPN lukker kun computere ind, hvis certifikat regionen har udstedt og ikke tilbagekaldt."},"whyItMatters":{"en":"Public keys are only useful if you know whose they are; PKI is what makes that answer trustworthy at the scale of the whole internet.","da":"Offentlige nøgler er kun nyttige, hvis man ved, hvem de tilhører; PKI er det, der gør det svar troværdigt i hele internettets skala."}},"deepDive":{"en":"A PKI has more moving parts than the certificate authority. The usual components are a root CA (offline, in an HSM), one or more issuing CAs, registration authorities that verify applicants, a repository for certificates and CRLs, validation services (CRL distribution points, OCSP responders), relying-party software that performs path validation per RFC 5280 §6, and the trust stores that define which roots are anchors. The governing documents are a Certificate Policy (what the certificates may be relied on for) and a Certification Practice Statement (how the CA actually operates), conventionally structured according to the RFC 3647 framework. X.509 itself dates from 1988 as part of the ITU-T directory standards; RFC 5280 is the internet profile.\n\nTrust models vary. The Web PKI is a set of independent hierarchies selected by browser and OS vendors through their root programs and governed by the CA/Browser Forum Baseline Requirements, with Certificate Transparency (RFC 6962; RFC 9162 defines version 2) as a public audit layer. Enterprise PKIs are private hierarchies, most commonly Active Directory Certificate Services, used for 802.1X network access, VPN, smart-card logon, S/MIME and device identity through Intune or other MDM. Bridge and cross-certified structures connect separate hierarchies, as in the US Federal PKI, and name constraints (RFC 5280 §4.2.1.10) limit a subordinate CA to specific namespaces. OpenPGP's web of trust is the main non-hierarchical alternative and has seen little uptake outside niche communities.\n\nEnrolment and life-cycle management protocols are where most operational work lies: ACME (RFC 8555) for automated domain-validated certificates, EST (RFC 7030), SCEP (RFC 8894) and CMP (RFC 4210, updated by RFC 9480) for devices and enterprise clients. With publicly trusted TLS certificates limited to 200 days since March 2026 and heading for 47 days by 2029, manual renewal is no longer viable, and certificate inventory becomes a core control.\n\nTypical failure modes are organisational rather than mathematical: an expired root or intermediate that takes down every service at once, an internal root key kept on an online domain-joined server, revocation infrastructure that nobody monitors so CRLs silently expire and clients fail closed, and certificate templates in AD CS that let any authenticated user request a certificate for a domain administrator (the ESC1 class of misconfigurations described by SpecterOps in 2021). PKI also has to plan for algorithm transitions; the move from SHA-1 to SHA-256 took most of a decade, and migrating hierarchies to post-quantum signatures such as ML-DSA (FIPS 204) raises the same problem with much larger keys and signatures. In Denmark, MitID Erhverv and the national OCES certificates are examples of PKI operated as public infrastructure, and eIDAS qualified trust service providers are audited under ETSI EN 319 411 and supervised nationally.","da":"En PKI består af mere end certifikatudstederen. De typiske komponenter er en rod-CA (offline, i en HSM), en eller flere udstedende CA'er, registreringsinstanser, der kontrollerer ansøgere, et repository til certifikater og CRL'er, valideringstjenester (CRL-distributionspunkter, OCSP-respondere), software hos den tillidshavende part, der udfører stivalidering efter RFC 5280 §6, og de trust stores, der bestemmer, hvilke rødder der er tillidsankre. De styrende dokumenter er en certifikatpolitik (Certificate Policy, hvad certifikaterne må bruges til) og en Certification Practice Statement (hvordan udstederen faktisk drives), normalt opbygget efter rammen i RFC 3647. Selve X.509 stammer fra 1988 som en del af ITU-T's directory-standarder; RFC 5280 er internetprofilen.\n\nTillidsmodellerne varierer. Web-PKI'en er en række uafhængige hierarkier, som browser- og styresystemleverandører udvælger via deres rodprogrammer, reguleret af CA/Browser Forums Baseline Requirements og med Certificate Transparency (RFC 6962; RFC 9162 definerer version 2) som offentligt kontrollag. Virksomheds-PKI'er er private hierarkier, oftest Active Directory Certificate Services, der bruges til 802.1X-netværksadgang, VPN, smartcard-login, S/MIME og enhedsidentitet via Intune eller anden MDM. Bro- og krydscertificerede strukturer forbinder separate hierarkier, som i USA's Federal PKI, og name constraints (RFC 5280 §4.2.1.10) begrænser en underordnet CA til bestemte navnerum. OpenPGP's web of trust er det vigtigste ikke-hierarkiske alternativ, men har kun fået udbredelse i snævre miljøer.\n\nProtokoller til udstedelse og livscyklusstyring er dér, hvor det meste driftsarbejde ligger: ACME (RFC 8555) til automatiserede domænevaliderede certifikater, EST (RFC 7030), SCEP (RFC 8894) og CMP (RFC 4210, opdateret af RFC 9480) til enheder og virksomhedsklienter. Når offentligt betroede TLS-certifikater siden marts 2026 højst må gælde i 200 dage og er på vej mod 47 dage i 2029, holder manuel fornyelse ikke længere, og et overblik over alle certifikater bliver en central kontrol.\n\nDe typiske fejl er organisatoriske snarere end matematiske: et udløbet rod- eller mellemcertifikat, der tager alle tjenester ned på én gang, en intern rodnøgle på en online, domænetilsluttet server, tilbagekaldelsesinfrastruktur, som ingen overvåger, så CRL'er stille udløber, og klienter afviser forbindelser, og certifikatskabeloner i AD CS, der lader enhver godkendt bruger bestille et certifikat til en domæneadministrator (ESC1-klassen af fejlkonfigurationer, som SpecterOps beskrev i 2021). En PKI skal også planlægge algoritmeskift; overgangen fra SHA-1 til SHA-256 tog det meste af et årti, og migrering af hierarkier til post-kvante-signaturer som ML-DSA (FIPS 204) rejser samme problem med langt større nøgler og signaturer. I Danmark er MitID Erhverv og de nationale OCES-certifikater eksempler på PKI drevet som offentlig infrastruktur, og kvalificerede tillidstjenesteudbydere efter eIDAS revideres efter ETSI EN 319 411 og er underlagt nationalt tilsyn."},"edges":[{"type":"requires","to":"cs/digital-certificate","confidence":"high","strength":"normal"},{"type":"requires","to":"cs/digital-signature","confidence":"high","strength":"normal"},{"type":"requires","to":"cs/public-key-cryptography","confidence":"high","strength":"normal"},{"type":"implements","to":"cs/authentication","confidence":"high","strength":"normal"},{"type":"used-with","to":"cs/tls","confidence":"high","strength":"normal"}],"depth":4,"sources":[{"title":"RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and CRL Profile","url":"https://www.rfc-editor.org/rfc/rfc5280","tier":"standard","publisher":"IETF"},{"title":"NIST SP 800-32 - Introduction to Public Key Technology and the Federal PKI Infrastructure","url":"https://csrc.nist.gov/pubs/sp/800/32/final","tier":"standard","publisher":"NIST"}],"draft":true}