Tarsnap preforms asymmetric encryption which lets you perform automated backups without needing to enter any passwords (or otherwise storing your encryption passwords in plain text).

Tarsnap does full deduplication across all backups for any given "machine", while still letting you independently remove any snapshots you like. i.e. no special "full snapshot" that must always be kept around, and no need for multiple full snapshots that have no deduplication between them.