--- title: SSH Certificates: How Do OpenSSH Certificates Compare to... description: OpenSSH uses its own certificate format (certkeys) instead of X.509, introduced since OpenSSH 5.4. The custom format extends existing public-key... canonical: https://daily.dev/posts/ssh-certificates-how-do-openssh-certificates-compare-to-x-509--33bpgo6wa twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: SSH Certificates: How Do OpenSSH Certificates Compare to X.509? | daily.dev og:description: OpenSSH uses its own certificate format (certkeys) instead of X.509, introduced since OpenSSH 5.4. The custom format extends existing public-key... og:url: https://daily.dev/posts/ssh-certificates-how-do-openssh-certificates-compare-to-x-509--33bpgo6wa og:image: https://api.daily.dev/og/posts/33BpGO6WA.png og:image:alt: SSH Certificates: How Do OpenSSH Certificates Compare to X.509? og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # SSH Certificates: How Do OpenSSH Certificates Compare to X.509? **[Teleport](https://daily.dev/sources/teleport)** · 7 min read · 0 upvotes · 0 comments ## Summary OpenSSH uses its own certificate format (certkeys) instead of X.509, introduced since OpenSSH 5.4. The custom format extends existing public-key authentication, reduces attack surface, avoids dependency on OpenSSL feature parity, and enforces separate CA hierarchies for users and hosts. However, it lacks X.509 features like cross-signing and CA hierarchies, and requires maintaining a separate CA. A detailed property comparison table and sample certificate outputs from ssh-keygen and OpenSSL illustrate the differences. Teleport is mentioned as a tool that manages both certificate types. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why does OpenSSH use its own certificate format instead of X.509? OpenSSH uses a custom certificate format (certkeys) to keep the implementation minimal and reduce attack surface compared to the full-fledged X.509 PKI. It also avoids dependency on OpenSSL implementing new features first, extends the existing public-key authentication protocol from RFC 4252, and enforces separate CA hierarchies for user and host authentication by default. _Comparing certificate formats for SSH access is easier when the tradeoffs are laid out clearly on daily.dev._ ### What are the main limitations of OpenSSH certificates compared to X.509? OpenSSH certificates require maintaining an additional certificate authority separate from any existing X.509 CA, since organizations commonly already trust an internal or external X.509 CA. They also lack support for cross-signing and managing multiple CA hierarchies beyond the basic user and host CA concept, which complicates large-scale CA rotation or migration. _Teams weighing SSH CA tradeoffs can track PKI comparisons like this on daily.dev._ ### What signature algorithms does OpenSSH support for certificates compared to X.509? OpenSSH certificates support SHA-256 and SHA-512 signature algorithms, while X.509 supports a broader range including MD2, MD5, SHA-1, SHA-256, SHA-384, and SHA-512, though MD2, MD5, and SHA-1 are considered insecure and should be avoided. OpenSSH also supports DSA, RSA, ECDSA, and EdDSA key generation algorithms. _Developers picking crypto algorithms for SSH auth can find comparisons like this on daily.dev._ ## Similar posts on daily.dev - [Jan-Piet Mens :: SSH certificates: the better SSH experience](https://daily.dev/posts/jan-piet-mens-ssh-certificates-the-better-ssh-experience-f1ftumowi) · Jan-Piet Mens · 0 upvotes · 0 comments - [SSH certificates and git signing](https://daily.dev/posts/ssh-certificates-and-git-signing-xbor3hzac) · Lobsters · 6 upvotes · 1 comments - [Stop managing SSH keys on every server and switch to Teleport](https://daily.dev/posts/stop-managing-ssh-keys-on-every-server-and-switch-to-teleport-zoja48gov) · All Things Open · 0 upvotes · 0 comments --- Tags: [#authentication](https://daily.dev/tags/authentication), [#cryptography](https://daily.dev/tags/cryptography), [#ssh](https://daily.dev/tags/ssh) [View this post on daily.dev](https://daily.dev/posts/ssh-certificates-how-do-openssh-certificates-compare-to-x-509--33bpgo6wa) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"SSH Certificates: How Do OpenSSH Certificates Compare to X.509?","url":"https://daily.dev/posts/ssh-certificates-how-do-openssh-certificates-compare-to-x-509--33bpgo6wa","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/ssh-certificates-how-do-openssh-certificates-compare-to-x-509--33bpgo6wa"},"datePublished":"2026-08-23T12:22:05.441Z","dateModified":"2026-08-23T12:43:14.169Z","description":"OpenSSH uses its own certificate format (certkeys) instead of X.509, introduced since OpenSSH 5.4. 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