There have been strange reports of how Safari just stops working (or decide to do it selectively) after a specified period. It's weird how a browser would run smoothly and, suddenly, you decide to choose where and when to run it. Many Mac users have encountered this strange error / hitch. Some websites will open without problems in Safari, while others will hit you straight with the now famous mistake “Safari cannot establish a secure connection to the server”.
What's even more puzzling is that the usual related fixes do nothing for the above error. Delete cookies, disable extensions, restart Safari, disable parental controls, scan keychains and reset permissions: all of this hits a brick wall. This error affects you even if you don't use a proxy to connect to the network. However, there is hope. The possible causes of this error have been reduced to several aspects.
Possible cause 1: ISP DNS
Click on the Apple icon and choose System Preferences. Then click on the Network icon and choose Advanced. Click on the DNS tab and remove the entries from the left panel, then click on the symbol + and add 8.8.8.8 and then click the plus symbol again to add 8.8.4.4.
Possible cause 2: weak encryption
When weak encryption is detected, Safari instantly disconnects the connection (It has not yet been determined which weak encryption detects first between Safari and Mac system). But we all know that for our privacy and security, websites must be accompanied by strong encryption before a web connection can be established unconditionally. This has been especially emphasized after the efforts of OS X Yosemite (Version 10.10.4) e iOS 8.4 will be boosted with additional security enhancements. Then, once weak encodings are met (or whatever the system presumes is weak), Safari will not be able to connect. This is how the error occurs “Safari cannot establish a secure connection to the server”.
Now let's see if we can figure it out once and for all. Once you are facing an encryption problem, the first place to look for an explanation is the certificates. Here's how to fix it
You experience the error in Safari but not in other browsers. Open the blocked web page (Facebook and Twitter are popular suspects) in another browser, for example, Firefox. Once opened, right next to the url, will identify a small green padlock. click on it. In the pop-up window, Click the button “more information”.
You should land in another window. Here, also click on the security tab on the right. Now click on “show certificate”. Switch to tab “Details”.
It will show you the current certificate of the website you opened. The syntax should look like this: “VeriSign Class 3 Public Primary Certificate Authority – G5 Certificate”
Then open the keychain. You can do it by clicking on CMD + space bar; then enter “Key chain”. Or go to Utilities and access Keychain from there.
Later, click system roots for all entries. Here you will find your certificate and it will have a blue cross marked. Double click on it and another window will appear. You have the option to choose a system configuration, always approve or always reject.
You will find that the certificate was the problem from the beginning. Normally, a certificate is locked on the mail server and prevents any other website from using it. (Your mail server should be the entry that begins with the prefix »smtp» and ends with the suffix ».dk«. The reason the certificate would crash on the mail server is as good as anyone could guess.
Change the certificate authentication to “System configuration”
There you go! All the pages you need will load perfectly in Safari. Problem solved.
NOTE: The above steps may vary slightly depending on the type of browser used (of course, except Safari itself)
Possible cause 3: antivirus
If you're not up to the task of manipulating certificates, it may be a good idea to check the antivirus installed on your machine first. As usual, Avast is a notorious culprit on this front. Turn off Web Shield and see what happens. Most likely, Safari will instantly connect to previously banned sites. It will be up and running, but still, no explanation why safari had worked before and it stopped suddenly. Good luck with that.
Possible cause 4: IPv6
If the option 2 it still doesn't work for you and you don't want to dig into the certificates, etc., try isolating the device from the Wi-Fi network you have been using. Connect it to another Wi-Fi network and see if everything opens up smoothly. If you can connect to all websites, including those previously blocked, disable IPv6 on your router (if available) and through System Preferences -> Red -> Your network -> Advanced -> Disable IPv6 from here selecting it as "Manual"
