The user for this question: How to get server's ssl certificate in a human readable form? asked if someone could add the tag [x509] to which I replied "no I don't think we need it".

In searching for it I only found 29 references to x509, seemed a little unnecessary to me.

  • Do others think we need this tag?
  • Do others concur?
  • X509 tag is now empty; please synonymize it with certificates.
    – Jeff Schaller Mod
    Sep 3, 2017 at 15:46

2 Answers 2


Do others think we need this tag?

For that questions I normally ask myself "Myself, what is ?" and myself answers with a wikipedia dump:

In cryptography, X.509 is an ITU-T standard for a public key infrastructure (PKI) and Privilege Management Infrastructure (PMI). X.509 specifies, amongst other things, standard formats for public key certificates, certificate revocation lists, attribute certificates, and a certification path validation algorithm.

Then, I look another posts/tags that already has what x509 means: "cetificates", "PKI", "PMI", "Privilege Management Infrastructure", "public key infrastructure", other related terms/tags. Now, is the proportion of related terms big enough that it will make it difficult for answerers find the questions they want to answer? No? Then we do not need a tag.

Remember that tags aren't there for the users asking questions but for the users to find questions they want/could answer ;). I do not think we have an important proportion of users that would like to answer those kinds of questions, so NO, we do not need that tag.

  • I concur. 1) I would expect anyone who knows what x509 is wouldn't be asking the question in that question. 2) It is a bit too specific to be useful. 3) It's more relevant to the answer than it is the question.
    – phemmer
    Dec 13, 2013 at 3:20

Technically, X.509 and certificates are not synonyms:

  • X.509 covers not only certificates, but also certificate requests and certificate revocation lists.
  • It would be possible to encode certificates in other formats.

At the level of this website, I don't see any distinction to be made between and . In practice nobody encodes certificates in anything other than X.509. If a question is specifically about certificate requests or certificate revocation, it can use a tag like or in addition to . So I think that and should be synonyms.

(Security.SE has separate tags, but even there I don't think it's warranted; I've raised that on their meta.)

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