See http://www.cryptar.com/ for a less technical description of
cryptar and for some information about release times.

Cryptar is rsync with an encrypted remote image.  That is, all data is
compressed and encrypted locally, then sent to the remote host (where
it is presumably useful to anyone but an authorized user with
password).  Cryptar keeps local metadata to remember what chunks live
on the remote host and so how to assemble diffs for further backup or
for restore.

A technical description of the algorithm lives in
paper/abrahamson04cryptar.pdf.  An updated version of the same paper
lives in that directory, with expanded sections concerning
applications and future directions.  The paper was accepted to the
2004 NordU/usenix conference.

    J. Abrahamson, A. J. O'Donnell, Cryptar: Secure, Untrustful,
    Differencing Backup, NordU/usenix conference, Copenhagen, Denmark,
    January 31 - February 1, 2004.

Sadly, cryptar is not finished, although much of its core
functionality works. There's still a lot of duct tape holding it
together.  I wrote this while doing my PhD, and so the product,
unfortunately, was the paper (conference presentation) rather than the
software.  The code is often ugly -- the cleanup and refactoring phase
never happened.  I am sometimes asked for the source code, however, so
I've posted it here.  There is an older repository on sourceforge,
which I should some day delete.

The code is old, from 2004.  I can make no promise that it still
compiles and works with modern versions of the libraries it uses.  At
the time, librsync was in its infancy and didn't seem usable for
this.  That may have changed as well, which would be nice.

Some day, in a world where I have a few spare weeks to do it, I'd like
to rewrite cryptar to be truly useful.  I would like to make it
comfortable with multiple devices, so that you can use it a bit like
Dropbox without the magic kernel integration: your files just appear
to be everywhere, locally cached but automatically updated to some
encrypted central place and replicated wherever you want them to be.
And I'd like there to be a free software version of JungleDisk, Mozy,
Carbonite, Dropbox, where you can host your own data if you want
anywhere that you can ssh to.

    Update:  Someday might have arrived.  The directory src/ contains
    	     code towards a new version, with planned support for ISP
    	     ssh (i.e., you have some disk space and ssh shell access
    	     with your ISP) and for AWS.  Although I'm doing ssh
    	     first.

	     I plan to make cryptar available as a library to IOS and
	     android apps to provide drop-in encrypted cloud storage.

	     Cryptar is licensed under the GPL, but I plan to offer
	     dual licensing (in the style of Sleepycat or Mysql).
	     This will probably involve a move from libbz2 to
	     lizlzma2.