Secure Connection Problems after Yosemite update

Question

Hi all
I'm using a MacBook Air 2012 and since upgrading to Yosemite, I have had a lot of issues using an Ethernet connection. I was using the same Ethernet connection for Mavericks and there were no problems whatsoever.
None of my apps which use the internet can connect. Examples include Skype not signing in, my Mail app not connecting and being unable to connect to the App Store.
When using Safari and Google Chrome I cannot access secure websites (https), however on Firefox I can access the majority of secure websites. Non-secure websites (http) are not a problem on any browser. Error messages on Safari say "Safari can't open the page (web address) because Safari can't establish a secure connection to the server." On Google Chrome the error message reads, "The connection to (web address) was interrupted."
I have tried and failed with numerous different suggestions including:
Ensuring correct time and date
DNS Flush
Changing Network Location in Preferences
Setting Network Location to Automatic in Preferences
Turning Firewalls/Anti-Virus Software off
Typing the following commands into the terminal:
          sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist
          sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist
Any help would be greatly appreciated!

Answer 1

Start up in Recovery mode. In the OS X Utilities screen, select Get Help Online. A clean copy of Safari will launch. No plugins, such as Flash, will be available. While in Recovery, you'll have no access to your saved bookmarks or passwords, so make a note of those before you begin, if they're needed for the test.
Test. After testing, restart as usual and post the results.