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Do any web browsers cache SSL server certificates? For example, if I change the SSL certificate on a web server, will all of the web browsers pick up the new certificate when they connect via SSL, or is it possible that they could have a stale certificate?

I'm thinking of the scenario when an SSL certificate expires and is replaced by a new one on the web server.

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I would assume the browser checks the date on the cert to see if it needs to get a newer one, like it does for everything else but am not sure. –  soandos Feb 16 '12 at 14:23
    
Have a look here imperialviolet.org/2011/05/04/pinning.html about "certificate pinning" and at the HSTS initiative whis is related to the former dev.chromium.org/sts –  Shadok Dec 14 '12 at 15:58

3 Answers 3

up vote 13 down vote accepted

No. See IBM SSL overview

  1. The SSL client sends a "client hello" message that lists cryptographic information such as the SSL version and, in the client's order of preference, the CipherSuites supported by the client. The message also contains a random byte string that is used in subsequent computations. The SSL protocol allows for the "client hello" to include the data compression methods supported by the client, but current SSL implementations do not usually include this provision.

  2. The SSL server responds with a "server hello" message that contains the CipherSuite chosen by the server from the list provided by the SSL client, the session ID and another random byte string. The SSL server also sends its digital certificate. If the server requires a digital certificate for client authentication, the server sends a "client certificate request" that includes a list of the types of certificates supported and the Distinguished Names of acceptable Certification Authorities (CAs).

  3. The SSL client verifies the digital signature on the SSL server's digital certificate and checks that the CipherSuite chosen by the server is acceptable.

Microsoft's summary is similar. The TLS handshake is also similar in this regard.

In step 2 there doesn't appear to be a way for the client to say "don't bother sending a server certificate, I'll use my cache".

Note that there are several types of certificates, client, server and CA. Some of these are cached.

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Amended original question to clarify that it's a server certificate. –  Lorin Hochstein Feb 16 '12 at 15:01

There are plans of some browser developers to implement such a chaching system for detecting attacks like the attack on Diginotar in 2011.

But at the moment AFAIK no such system is active in current browsers. Therefore you don't have to think about this situation when updating your server certificate.

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Well, the answer by RedGrittyBrick is correct, but not really answering the question. The question was, if browsers do it, not if they should or need to do it.

From what I've heard, both MSIE and Chrome actually do cache certificates, and don't replace them when they get a new version as long as the old one is valid. Why they do this is not for me to understand, as it lowers security.

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The currently accepted answer is pretty clear. It specifically indicates that, no, browsers do not cache the certificates. As you point out the landscape changed, the reasons Chrome does, is well documented would be nice for you to link to those reasons. Since the certificate is still valid it doesn't "lower" the security that wouldn't make sense. –  Ramhound Feb 5 at 12:05
    
It does lower it, because you can't replace an old SHA-1 key with a newer one, because the old one still is valid, and Chrome ignores the new one, if I understood everything right. So there's no way of enforcing a switch to higher security standard - so it "lowers" in a relative sense by not enabling to push it higher. Just like inflation doesn't lower your money designated value, but its actual market value. –  tuexss Feb 6 at 18:46

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