I just now need a deduplicating asymmetrically encrypted backup program.

I've tried duplicity in the past, and maybe I should try it again. But my recollection is that duplicity will just fail to do backups at the slightest hint of any problem. Like maybe if the last backup was interrupted then no more backups for you until you attend to it.

Edit: More memories returning of having to dig out my decryption key to resync the metadata when duplicity gets unhappy, and then since my target server was append-only, duplicity was upset when it wasn't allowed overwrite any of it's incomplete metadata files. I guess the ZFS snapshot technique would alleviate the latter issue.

To be fair, if tarsnap gets confused it needs the keys to do its fsck command, but I recall this sort of thing happening regularly with duplicity and almost never with tarsnap.