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I understand on a conceptual level that a certificate is nothing more than just a verified public key. The next question I have, is how exactly do I see the contents of a certificate? Apart from the public key it verifies are there other information that the certificate contains? Does the certificate also contains the signature of the public key etc. etc.

Pointers on how to further explore certificates would be appreciated!

Edit I am mostly thinking about the ones used with HTTPS/TLS

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    $\begingroup$ What type of certificates are you referring to? $\endgroup$ – Modal Nest Dec 24 '20 at 14:08
  • $\begingroup$ updated to mention certifictaes used for https/tls $\endgroup$ – Finlay Weber Dec 24 '20 at 14:55
  • $\begingroup$ Most browsers have ways to view certificate details for the server(s) you're connecting to, as well as to save them as files so you can run other programs to display their info -- but of course, they depend on which browser and OS you're using. I recommend searching the web for e.g. how can I view tls certificates with firefox. $\endgroup$ – Gordon Davisson Dec 24 '20 at 22:21
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HTTPS/TLS uses X.509 certificates generally. There is more detail here in the latest TLS specification.

You can view HTTPS certificates in a browser.

As per Wikipedia:

The structure of an X.509 v3 digital certificate is as follows:

Certificate

  • Version Number
  • Serial Number
  • Signature Algorithm ID
  • Issuer Name
  • Validity period
    • Not Before
    • Not After
  • Subject name
  • Subject Public Key Info
    • Public Key Algorithm
    • Subject Public Key
  • Issuer Unique Identifier (optional)
  • Subject Unique Identifier (optional)
  • Extensions (optional)

Certificate Signature Algorithm
Certificate Signature

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    $\begingroup$ lapo.it/asn1js is probably worth a mention. In-browser ASN.1 decoder. JS version of Gutmann's dumpasn1. Very handy. Available as a zip for use offline (EG when dealing with private data). It even has some examples of both PKCS#7/CMS and X.509 certificates. $\endgroup$ – SAI Peregrinus Dec 25 '20 at 4:44
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Besides browsers, you use KeyStore Explorer. With it you can not only view certificates, you can also view key stores, you can create CSRs (Certificate Signing Requests). It is free and open source. It works on any of major operating systems.

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Most of the systems I work with are of Linux based, and use OpenSSL to view/verify the certificate.

  • You can check 'openssl' commands to view its contents.
  • Other than public key people use expiry date, to validate the client uses the right latest one.
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