When you need to keep files on a remote system synchronized, you want to protect its contents should it end up in the wrong hands. You can use rsync to keep the contents up to date, but natively no encryption method is used. Rsyncrypto is an encryption package aimed at transferring the changed blocks of a file with encryption, making for a more efficient transfer during the synchronization operations when using rsync.
Installing is quite easy by downloading the tar file, then extracting and running the ./configure script. I used a C++ compiler and argtable2 on a CentOS 4.2 system during a test implementation.
Once you have installed rsyncrypto, you can set up encryption for files to be synchronized as they change, with the encryption on blocks of the file with a specified key. Please note, this encryption within rsyncrypto is not as robust as some of the newer PGP encryptions (like GnuPG) when using rsync for an entire file. Rsyncrypto is currently at version 1.06 and is currently available for download from SourceForge.