Category: Cryptography

GPG symmetric encryption: Passphrase on command line

Uli Köhler Cryptography

Problem:

You want to use GnuPG’s –symmetric encryption, but instead of interactively entering the password you want to use a command line argument with the cleartext password.

Solution:

Use --batch --yes --passphrase <passphrase>:

gpg --symmetric --batch --yes --passphrase 12345 <input file>

Note that this is potentially insecure as it’s way easier to find out the command line parameters of running programs than intercepting the inputs of the interactive input dialog. Therefore, use this strategy only if neccessary.

How to automatically renew Let’s Encrypt certbot certs on Ubuntu

Uli Köhler Cryptography, Linux

On Ubuntu, you can easily setup a daily job that tries to renew almost-expired Let’s Encrypt certificates.

Create /etc/cron.daily/renewcerts:

#!/bin/bash
certbot renew
service nginx reload

After that, sudo chmod a+x /etc/cron.daily/renewcerts.

Now you should verify that the script would actually run:

run-parts --test -v /etc/cron.daily

should print, among other lines, this line:

/etc/cron.daily/renewcerts

IMPORTANT: You still need to run certbot renew manually every 1-2 months to check if there are any errors that might prevent certs from being renewed.

NOTE: Since the script is calling service nginx reload, you need to ensure that your nginx config files are not left in a broken state for too long if you edit them. Use sudo nginx -t to check for errors after you edit them. Also note that if you make nginx config changes, the script might unintentionally apply them to your productive HTTP/HTTPS server!