Why you need to renew your SSL certificates



More precisely, then SSL / TLS certificates. If you look soberly, then only TLS should be used now . But the certificate is something for SSL, one for TLS. And they call it all out of habit “SSL certificate”.

This article is intended primarily for web server administrators. The reason you might have to renew your server certificate ahead of schedule is because the widespread SHA-1 hash algorithm is considered unsafe today.

“What does hashing have to do with it? Certificates are based on asymmetric encryption, ”some will say. The fact is that a certificate is not just a public key with additional information, but also a server signature, and a hash function is used for it.

The persistence of a hash function is the absence of collisions. That is, the inability to pick up a message different from the original one with exactly the same hash value. Simply put, regarding certificates: a hash function is good if it is impossible (it should be read “extremely difficult”, since there is nothing impossible) to forge a certificate, but leave the same signature on the certification center (CA). Thus, a fake certificate can turn out to be quite valid from the point of view of browsers, operating systems and, in general, from the point of view of a completely sane check. So the resistance to collisions of the SHA-1 algorithm is in very great doubt. The famous cryptographer Bruce Schneier calculated that the implementation of the collision attack on SHA-1 will be fully within the powers of organized crime by 2018.

So, we have come to the conclusion that it will become unsafe to use SHA-1 for signing certificates in the near future. And, of course, SHA-2 is called to replace SHA-1. Microsoft and Google are taking some steps to speed up the migration process to SHA-2.

Google


In the next version of the Chrome browser at number 41, there will be such a reaction to certificates using SHA-1:
  1. If the certificate expires after 2016, the user will see a red cross on the lock and a crossed-out https.
  2. If the certificate ends in 2016, there will be a warning yellow triangle on the lock.


Microsoft


If your certificate using SHA-1 for signing ends in 2017 or later, then you will have to change it ahead of schedule. And this applies not only to certificates of web servers, but also certificates for signing the code. In addition, since the beginning of 2016, Microsoft has ceased to trust certificates with SHA-1, which are used to sign code without a time stamp.

What to do?


The answer is simple. If you want to prevent users of your online store or corporate portal from opening a page with a certificate error, update it in advance.

It is worth considering that for successful certificate validation it is necessary that all certificates in the chain use SHA-2. But if the root CA uses SHA-1, then you should not worry much, because browsers do not check the signature of the certificates of the root trusted CAs, but simply look for them in the corresponding list.

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