rdiff is a little like diff and patch all rolled into one, with support for
 binary files. Since it takes advantage of the rsync remote-delta algorithm, you
 do not need the source file in the same place as your destination file.
 .
 To use it, you generate a "signature" of the original file and copy the
 signature (which is very small) to the same location as the modified file. Then
 you generate a "delta" which describes the changes required to turn the source
 file into the modified file. The small delta file can then be used to "patch"
 the original file, to transform it into the modified file.