i had an interesting idea: to modify rsync to combine encryption into it, using CBC-mode block ciphers instead of md4 checksumming.
what you would do is, every <blocksize> bytes, perform a single encrypt of a sequential number (or a pre-seeded pseudo-random number generator) and that one block becomes your checksum.
you _would_ need to store those checksums on the server (and the checksums should be stored on the server _anyway_ to save processing power!)
The Plan is, ultimately, to safely and efficiently perform secure backups.
i wish rsync already had a VFS layer, i really do.