Thanks. I think that is the problem. I just installed this on Ubuntu 14.04 and it looks like it is using version 2.6. However in the tutorial they are installing version 3.0
I also checked Ubuntu 16.04 and 17.10 and they are all using this old version. It is possible that this feature was not added until a later version.
In order to get this to work, I would uninstall the version that you installed with apt
apt-get remove automysqlbackup and install this manually with the following steps.
tar zxf automysqlbackup-v3.0_rc6.tar.gz
Once you have ran the install script, you should see the up to date file located in
/etc/automysqlbackup/automysqlbackup.conf and be able to change the settings for encryption. They should look something like this:
# Do you wish to encrypt your backups using openssl?
# Choose a password to encrypt the backups.
Be sure to replace
$YOUR_PASSWORD with whatever password you want to use.