The File Extensions Database

.CER File Extension

  • Category: Web Files
  • Format: Binary

What is an .CER file?

.CER is Internet Security Certificate

A CER file is a security file provided by a third party Certificate Authority, such as VeriSign or Thwate, that verifies the authenticity of a website. It is installed on a web server to establish the validity of a certain website hosted on the server.

CER files can be viewed by clicking the lock icon near the edge of a browser window when accessing a secure site (secure sites use SSL encryption as seen by the "https://" prefix in the URL).

Secure certificate information can be viewed in Internet Explorer and Firefox by double-clicking the lock icon located near the bottom-right corner of the browser window. To view the certificate in Safari, click the lock icon located near the top-right corner of the browser window.

Programs that open Internet Security Certificate
Microsoft Internet Explorer
Mozilla Firefox
Adobe Acrobat Reader DC
Adobe Acrobat DC
Apple Safari
Mozilla Firefox
Adobe Acrobat Reader DC
Adobe Acrobat DC
Apple Keychain Access
Mozilla Firefox
Adobe Acrobat Reader DC

How to solve problems with CER files

  • Associate the CER file extension with the correct application. On :
    Windows: Right click on any CER file and then click "Open with" > "Choose another app". Now select another program and check the box "Always use this app to open *.CER files". Mac: Right click (or Ctrl-click) the CER file, then click "Open with" > "Other...". Then choose another program and check the "Always Open With" box. Linux: Right click on the file, and select "Open with" and choose another program. iPhone: Tap the file. If you do not see an app to open the file, then tap Share "Share" and choose an app. Alternatively, save the file. Then open the Files app Files app. There long-press on the file, then release your finger. You will see a black menu bar. Then tap "Share" and select an app. Android: Tap the Settings icon on your smartphone, then tap on the Apps section. There tap the Options icon in the top right-hand corner of the screen to change the default apps.
  • Update your software that should actually open .CER is Internet Security Certificate. Because only the current version supports the latest CER file format. Search, therefore, e.g. on the N/A manufacturer website after an available .CER is Internet Security Certificate update.
  • To make sure that your CER file is not corrupted or virus-infected, get the file again and scan it with antivirus software.