Serendipity is of course the best availiable blogging software out in the wild. But you can even make it better. For example with rewrite rules. The following rule enforces HTTPS on your administration panel:

RewriteEngine On
RewriteCond %{REQUEST_URI} ^/serendipity_admin\.php$
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}/$1 [R=302]