GPG
https://www.debian-fr.org/t/guide-autodefense-courriel-gpg-e-mail-closed-lock-with-key/68890
https://begriffs.com/posts/2016-11-05-advanced-intro-gnupg.html
https://www.nextinpact.com/news/102685-gpg-comment-creer-paire-clefs-presque-parfaite.htm