Rsyncrypto[1] is a file encryption tool. It has a single RSA key that encrypts symmetric AES keys per file. The files themselves are subject to an encryption method that is based on CBC, but does a security-performance trade off. In particular, the files are encrypted in such a way that re-encrypting, using the same key, a file that was slightly modified will result in slightly modified cypher text. This is needed so that the file will retain wire efficiency when transferred using rsync[2].
http://www.securiteam.com/unixfocus/5OP0L0UOAS.html
