I wanted to setup encryption with dm-crypt and LUKS, but I set it up manually, not during installation process (I created LUKS partition and /etc/crypttab file properly). But the encrypted partition defined in /etc/crypttab doesn't mount at boot at all. Otherwise, when mounted manually, everything works.
It was a clean Ubuntu 13.10 install.
The problem is, that only package cryptsetup-bin is installed by default on ubuntu 13.10 (and AFAIK on older versions). That means, that you can create and manipulate dm-crypt partitions, but you also need cryptsetup package, which contains startup scripts for mounting dm-crypt volumes at boot.
sudo apt-get install cryptsetup solved that problem.