I use rsync (also called deltacopy) to a copy a large (6GB) text file (SQL database dump) on to a remote server. this gets me about 100:1 bandwidth reduction over simply copying the file as most of the content us unchanged day-to-day
This is a single file which contains all the data in the database, rsync compares the content piece by piece with the destination content (using hashes) and only sends the hashes and the changed parts down the wire.
I can instead produce a dump with one file per database table, but the Only tables likely to be unchanged day-to-day are small.
I want to start encrypting this file at the source, and storing only encrypted copies at the destination, but it seems to me that any encryption stronger than a simple substitution cypher is going to compromise the efficiency gain I get from using rsync.
Is there some strong encryption that I can use for this purpose?