extension of rsync on crypted files

jw schultz jw at pegasys.ws
Thu Jun 27 13:02:05 EST 2002

On Thu, Jun 27, 2002 at 03:26:51PM +0200, Mikael moshir wrote:
> Hello,
> I am a french student and I have written a technical
> report on  an extension of the rsync algorithm to crypted
> files.  I started from the situation of a client machine A
> user who doesn't wish to save an original file v0 and its
> successive versions v1 v2 v3 ... on a distant server B but
> rather to save the private ciphering of these files on the
> server. Let C be the cipher algorithm and xi=C(vi) the
> ciphering of the clear file vi, the client A wishes to
> save x0, x1, x2... on the server B and not v0,v1.... This
> situation arrises for secured files backup providers which
> offer an option of a secured and confidential file's
> history backup - a client can keep the history of a file. 
> Trying to use rsync here is not a good solution  because
> the ciphering transformation on file versions disperses
> the correlations between them and then when Rsync tries to
> localize common blocks between ciphered versions, he
> hardly ever finds and the compression resulting from the
> common sequences factorisation can't happen.
> My method proposes a solution to this problem and allows
> to save ciphered versions on a distant server with costs
> (storage, communications, algorithmic complexity)
> comparable to rsync.  I want to know if anyone finds my
> work of interest and if anyone of you knows if such a
> problem have been adressed before.  I keep the
> documentation of my article (in french but i am working on
> an english translation) for anyone who would have more
> details.  Thank you!
> Ps: sorry for my small english skill.

That skill is sufficient but you need shorter lines (hit the
carriage return).

I will try to clarify since it looks like this hasn't been

	plaintext == unencrypted file
	ciphertext == encrypted file
	client == local system
	server == distant system

You have a client with plaintext files.  The server provides
access to multiple versions of files but on the server they are

As you have described it this sounds a great deal like a SCM
(source code management) system with encryption thrown in.

Presumably the encryption is because the user doesn't wish
to trust the owner of the server with maintaining his

Judging by several recent threads there are quite a few
people who could be interested.  I suggest you look in the
list archives for the word "encrypt".  You speak of a
technical report that i assume actually discusses the
method.  If you can distill that down (cut out the academic
verbiage and focus on actual method sans proofs) to a couple
of hundred words or less you could post it for discussion.
A link to source code wouldn't hurt.  We focus here on what
actually works and even broken code speaks louder than

	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt

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