Un bon tuto sur la configuration de Let's Encrypt sous Debian 10 Buster.

sudo openssl dhparam -out /etc/ssl/certs/dhparam.pem 4096

sudo certbot certonly --agree-tos --email admin@example.com --webroot -w /var/lib/letsencrypt/ -d example.com -d www.example.com --rsa-key-size 4096