Convert a CER certificate to CRT with OpenSSL

A first thing to understand is that a CER certificate can be encoded either in PEM or in DER.

DER is a binary format while PEM is a base64 encoding.

The .cer extension simply means "certificate", we quite often find either .cer or .cert.

Convert to CRT with OpenSSL

To convert a .cer certificate to .crt with OpenSSL you need to use the following command:

openssl x509 -inform DER -in monCertif.cer -out monCertif.crt

If you encounter an error, your certificate may be PEM encoded. Two solutions are therefore available to you, either regenerate a .cer certificate encoded in DER, or use the following command:

openssl x509 -inform PEM -in monCertif.cer -out monCertif.crt

Hint:

To directly use the "openssl" , you just need to add the "bin" of your OpenSSL installation in the PATH environment variable of your machine.

Go to => Control Panel\System and Security\System

Click "Advanced system settings"

then "Environment Variables..."

And add the folder path "bin" of your OpenSSL installation

There you go, that’s it, enjoy!