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.
44 Answers
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.
6No. See IBM SSL overview
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.
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).
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.
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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.
3I'm not sure if my input will help in any way but here's what I've just experienced: I've got a web site in azure with a custom domain. I tried accessing it with https in chromes before configuring the SSL binding for my domain name. Chrome was telling me that the site is not secured which perfectly makes sense (ERR_CERT_COMMON_NAME_INVALID) But after I uploaded my cert and configured the SSL binding in azure I was still getting the same error. At this stage, when opening a new private browser window (or using another browser) the https was working fine.
But I could never get it to work in my open Chrome session. I tried clear SSL state, same result. It worked after restarting chrome altogether.
I was probably tricked by something but it almost looked like the cert was cached...
7There 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.
