There are several options for encrypting and decrypting a single text file on Ubuntu using both GUI applications and command-line tools.
Gnome Encfs Manager: It's a GUI for EncFS. EncFS is a userspace filesystem that allows you to mount an EncFS directory on your filesystem, and all data written to that directory is encrypted, and all data read from that directory is decrypted. Gnome Encfs Manager can be installed via the Ubuntu Software Center or from the terminal using the command
sudo apt-get install gnome-encfs-manager.
seahorse: It's a GUI tool for managing your encryption keys and passwords. It can also be used to encrypt files and folders by creating an encrypted tarball. It can be installed via the Ubuntu Software Center or from the terminal using the command
sudo apt-get install seahorse
Gnu Privacy Guard (GPG): It is a free, open-source implementation of the OpenPGP standard for encrypting and signing messages. You can encrypt files with GPG by running the command
gpg -c file.txt, which will create an encrypted file called
file.txt.gpg. To decrypt the file, you would run the command
OpenSSL: It is an open-source implementation of the SSL and TLS protocols, and it includes a command-line tool for encrypting and decrypting files. To encrypt a file with OpenSSL, you can run the command
openssl enc -aes-256-cbc -salt -in file.txt -out file.txt.enc. To decrypt the file, you would run the command
openssl enc -d -aes-256-cbc -in file.txt.enc -out file.txt.
tar: This command line tool allows you to create archive of files and directories with the option of encrypting them using
gpg. For example,
tar czvf - file.txt | gpg -c -o file.txt.tar.gz.gpg this will create an encrypted archive of the file.txt, and for decrypting
gpg -d file.txt.tar.gz.gpg | tar xzvf -
These are just some examples of the various ways you can encrypt and decrypt files on Ubuntu, depending on your needs and comfort level with command-line tools. Be sure to keep a secure backup of your encryption key or password in case you lose it, otherwise, you won't be able to decrypt your files.