Rsyncrypto is a modified encryption scheme. It is based on industry standard
AES for symmetric encryption, as well as RSA for having different keys for
each file while allowing a single key to decrypt all files. It even uses an
encryption mode that is based on CBC.

Rsyncrypto does, however, do one thing differently. It changes the encryption
schema from plain CBC to a slightly modified version. This modification ensures
that two almost identical files, such as the same file before an after a
change, when encrypted using rsyncrypto and the same key, will produce almost
identical encrypted files. This means that both objectives can be achieved
simultaneously.

WWW: http://rsyncrypto.lingnu.com/