Rsyncrypto

Sometimes it is necessary to store files on a remote server. This is typically needed for backup purposes. When that is done, there are two concerns that need to be addressed: How to keep the Privacy of the files stored? How to keep bandwidth usage to a minimum? Both problems have rather simple solutions: Encrypt the files prior to sending them. Keep the key locally. Use rsync to only transfer the changes. There is just one problem - the two solutions contradict. Plain mode encryption of files hide the specific changes to the file, making rsync useless at detecting in-file changes. This is where rsyncrypto comes to the rescue. 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. Rsyncrypto has won first prize in the free software Trophy competition in the security category.