Deadbolt is a free open-source file/ folder encryption tool.
If you're running Mac OS, install deadbolt with Homebrew:
brew install --cask deadbolt
deadbolt simplifies encrypting and decrypting files. All you need is a password.
Select a file to encrypt, enter a password, and … that’s it. Decryption is just as easy.
You can download deadbolt for Mac OS, Windows, or Linux. Any encrypted file can be shared across these platforms.
Note: deadbolt can not encrypt directories. To encrypt a directory, compress it into a .zip (or any archive format) file before using deadbolt.
Linux (Ubuntu and Debian)