There are numerous ways to encrypt a file or a directory under Linux.
Some of these methods involve deploying specific encryption utilities or public/private key systems such as gpg.
I wanted to deploy a simple method that relies on mainstream tools which are usually present on most if not all Linux systems.
The method described below uses tar and zip/unzip.
Create a Tar Archive
First, tar the folder into a .tar archive:
tar -cvf folder.tar /folder
Create a Password Protected Compressed File using zip
then zip the .tar file:
zip -re folder.tar.zip folder.tar
it will prompt you to enter a password of your choosing and then verify it
HOWEVER, note it will still be possible to display a file listing of the contents of the .zip file.
To conceal the contents, you next need to place this created zip file in another folder and then zip compress this folder in turn, also applying password protection.
The contents of the zip archive file will then be fully password-protected.
to unzip you have to use
This will prompt you to enter the password
tar -xvf folder.tar
this then recreates the directory structure and the contents