Why you need to update your SSL certificates

More specifically, SSL / TLS certificates. If you look soberly, you should now use only TLS. But the certificate is what for SSL, what for TLS is one. And they call it all out of habit "SSL certificate".

This article is intended primarily for web server administrators. The reason you may have to renew your server certificate early is that the common SHA-1 hash algorithm is considered insecure today.

“What has this to do with hashing? 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.
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The persistence of a hash function is the absence of collisions. That is, the inability to select a different from the original message with exactly the same hash value. Speaking easier and regarding certificates: the hash function is good, if it is impossible (you should read “extremely difficult”, since there is nothing impossible) to forge the certificate, but leave the same signature of the certification authority (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 very doubtful. Well-known cryptographer Bruce Schneier calculated that the implementation of a collision attack on SHA-1 will be fully within the power of organized crime by 2018.

So, we come to the fact that soon it will become unsafe to use SHA-1 to sign certificates. And, of course, SHA-1 is intended 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 Chrome browser at number 41 there will be such a reaction to certificates using SHA-1:

1. If the expiry date of the certificate is after 2016, the user will see a red cross on the padlock and the crossed-out inscription 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 expires in 2017 or later, you will have to change it early. And this concerns not only certificates of web servers, but also certificates for code signing. 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 the users of your online store or corporate portal not to shut down the page with a certificate error, update it in advance.

It should be borne in mind that for the successful validation of the certificate 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 too much, because browsers do not check the signature of root trusted CA certificates, but simply look for them in the corresponding list.