Using the Command Line to Decrypt a Message on Linux
If you have disabled the PGP plugin from your mail client and saved a copy of an encrypted email to your desktop, this guide will help you read that message in as safe a way as possible given what we know about the vulnerability described by EFAIL.
Note that the first three steps (opening the terminal) will vary between desktop environments.
Open the Activities view by clicking all the way in the top left corner of your screen.
2. Type “terminal” into the search bar, and press Enter. This will open the command prompt.
3. Type “cd Desktop” to go to your desktop. Mind the capital ‘D’!
4. Type “gpg -d encrypted.eml” using the name of the file you saved earlier. This may prompt you for your PGP passphrase depending on your configuration and recent usage, and will output the full email in the terminal window.
These notes are based on Ubuntu Desktop with GNOME 3.