Ask HN: Remote encrypted backup recommendation?

I've been researching my backup requirements lately, and my requirements are:

* Encrypted, trusted (this implies open source) backups.

* Able to backup to a remote server. Google Drive is a plus.

* Not terribly bandwidth intensive.

* Not terribly expensive, as I'm backing up non-critical photos which are already on RAID and local backups anyway.

I'm currently using SpiderOak, but I don't like the fact that it's closed source. I experimented with Duplicity, but it turns out that it requires me to reupload my entire 50 GB collection every month or so, as it's good sense to have full backups every so often.

The problem is that, even though I require encryption, it shouldn't roll all files into a huge ball of mud, as that will need reuploading every once in a while, it's not easy to sync, etc.

Basically, the ideal for me would be something like Duplicity with per-file encryption, or rdiff-backup with encryption. Is there something that would fit the bill, or would I have to build it myself?