Getting "not secure" prompts for certain sites using macOS X El Capitan 10.11.8

On the 30th of September 2021 the certificates that allow oyou to connect to various websites expired you can however download new ones.

Click on the link below,

https://letsencrypt.org/certificates/

Down load these two files

ISRG Root X1

Self Signed click on the der to download

And ISRG Root X2

Self signed click on der to download.

Open the Keychain Access app in your Applications> Utility folder.

In the left column highlight System.

Click on File in the menubar and click on Import Items,

select the newly downloaded files in turn and press Open.

Double-click on one of the newly imported certificates, click on the disclosure triangle

and next to When using this certificate: change Use System Defaults to Always Trust.

Do the same for the other certificate.

Restart your mac.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina & Big Sur supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation

Upgrade the OS, or use another web browser, or choose Utilities from the Finder's Go menu, open the Script Editor, and run:

do shell script "curl -k https://letsencrypt.org/certs/isrgrootx1.der > ~/Downloads/isrgrootx1.der"

Double-click the downloaded certificate.

(206168)

As I said my version pre patch opened the website,

I got the 'Certificate expired' dialogue with the chance to view the Certificate and also Continue,

pressing Continue allowed me to open the website download the new certificates and carry on.

DOWNLOADING INSTALLING AND SETTING THE NEW SECURITY CERTIFICATE FOR GOOGLE CHROME ON EL CAPITAN

This worked 100% on my 2008 Mac Pro Tower running El Capitan, which is extremely fast and reliable for its age, but I cannot install Sierra on it.

Instructions

Go to

https://letsencrypt.org/certificates/

Find the newest of this file link (first on the page)…

“Signed by ISRG Root X1: der, pem, txt”

Click on pem to download the correct one.

(I have my browser set to always download to the Desktop so I can quickly find the stuff I just downloaded, and I put it where it goes later).

Open Keychain Utility in the Applications > Utilities folder

Enter your password every time asked.

Click System (upper left)

Drag the new Security Certificate from the Desktop into the Security page in the open Keychain Window.

Double click on the new Security Certificate.

Click the little arrow next to “Trust” at the top to expand it.

Choose “Always Trust” in the menu next to

“When using this certificate:”

You can choose “Always Trust” because it literally just came from the website of the company that creates the Trusted Certificates.

The new Security Certificate is literally coming from the company that creates Security Certificates. I think that would be pretty safe. Other than that... Never put your info on a website without a lock showing in the address box, etc...

HOW TO DOWNLOAD, INSTALL, AND SET THE NEW SECURITY CERTIFICATE FOR GOOGLE CHROME & SAFARI ON EL CAPITAN

This worked 100% on my 2008 Mac Pro Tower running El Capitan (extremely fast and reliable for its age, but cannot install Sierra on it).

INSTRUCTIONS

Go to

https://letsencrypt.org/certificates/

Root Certificates

Active

ISRG Root X1 

Find the newest of this file link (first on the page)…

“Signed by ISRG Root X1: der, pem, txt”

Click on pem to download the correct one.

(I have my browser set to always download to the Desktop so I can quickly find the stuff I just downloaded, and I put it where it goes later).

Open Keychain Utility in the Applications > Utilities folder

Enter your password every time asked.

Click System (upper left).

Drag the new Security Certificate from the Desktop into the Security page in the open Keychain Window.

Double click on the new Security Certificate.

Click the little arrow next to “Trust” at the top to expand it.

Choose “Always Trust” in the menu next to

“When using this certificate:”

You can choose “Always Trust” because it literally just came from the website of the company that creates the Trusted Certificates.

Paste the entire line into the Script Editor instead of using your web browser.

Eau Rouge: The expired certificate prevents Safari from accessing that page.

(206180)

Really I managed to get through on my copy of El Capitan.

If you applied the patch to your system, it'll work.

(206214)

This works. Many thanks

I have read all of the responses and cannot make them work. I am only soso tech savy. Am running El Capitan 11.6.8. I use Chrome but tried Safari and same thing. Any help in lay person's terms?

How do I know this is not going to open my computer up to hackers etc? I am sorry to be so suspicious but dam it's a jungle out there. I am hoping to give this a try anyway!