I have the Certificate Patrol addon (website) installed in Firefox. While I mostly ignore the (far too many) warnings, today I saw that the certificate authority for my personal website has changed. This certificate is created by myself, self signed, and I didn't change anything for the past month or two.

I made a screenshot of the warning, and see two different SHA1 fingerprints. MD5 fingerprint changed from - to undefined. Organization name (O) changed as well from unknown to the name I gave it. I didn't click the "view certificate" buttons for both websites, and regret that now.

  • What does this mean? Can I trust the certificate?
  • How can I check that my certificate is still valid, created by me, not changed by someone or something else?
  • Should I recreate it?
  • 1
    Is this a self signed cert? – StackzOfZtuff Jun 20 '15 at 19:41
  • Yes, it is self signed. – SPRBRN Jun 20 '15 at 19:44
  • 2
    What does your website do, and what does it run on? Some software packages I've seen automatically generate their own self-signed certs every once in awhile, though most come with a default cert that everyone with the package gets to start with, unfortunately. – Anti-weakpasswords Jun 21 '15 at 0:14
  • The certificate is created by openssl, and is used by Tomcat 7 on a Ubuntu 14.04 server. I see that the validity period is only three months. I created it one month ago, in two months it's not valid anymore. I thought it would last longer, but apparently I didn't set that right. – SPRBRN Jun 21 '15 at 9:57

What does this mean?

The certificate changed, as shown by the different SHA1 hashes. The MD5 hash field is no longer relevant as Firefox deprecated them.

Can I trust the certificate?

No, if it changed without the admin (ie. your) intervention, you should be highly suspicious.

How can I check that my certificate is still valid, created by me, not changed by someone or something else?

You should compare the new certificate with the copy/hash you kept locally when creating it. Because you wrote it down, right?

Should I recreate it?

Not necessarily. If your certificate were compromised, it wouldn't have been detectable. OTOH, if you're not sure which certificate you created, generating a new one would be appropiate.


Although this shows that there was a man-in-the-middle attack on you/your website, probably the new (forged) certificate was generated by a captive portal or even your router, and not someone targetting you at the network level.

  • Thanks for the explanation. The key was created one month ago, and is two more months valid. I may have entered a wrong date, but normally I would use a certificate that is valid for at least a year. I'm going to recreate it, and then write the hash down, and be more alert about it. – SPRBRN Jun 21 '15 at 10:01

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