Encrypt External Hard Drive for Mac and Linux

I have an external hard drive that I backup with Time Machine. I'm trying to determine the best way (or if it's even possible) to encrypt it so that Time Machine can still back it up and it can be mounted and read by my Ubuntu server. I'm not hoping for write access but that'd be even better.

I've looked into way to read File Vault 2 volumes on Ubuntu but haven't found anything too promising. So I'm assuming I need to go with something like TrueCrypt but am not sure how Time Machine will handle that.

The driver is currently formatted with OS X extended but I can format if needed.

The easiest way to handle this situation is to buy a drive that uses OS-agnostic hardware encryption, then format it with a format which is readable by both OS X and Linux. Since both Time Machine and Ubuntu are referenced, you may want to install hfsprogs in order to enable Ubuntu to read OS X's HFS+, then format the drive itself as HFS+:

http://packages.ubuntu.com/trusty/otherosfs/hfsprogs