Re: Secure backup on remote untrusted server over slow line?

From: Kasper Dupont (kasperd@daimi.au.dk)
Date: 06/13/02 

From: Kasper Dupont <kasperd@daimi.au.dk>
Date: Thu, 13 Jun 2002 02:21:11 +0200

Preben Bohn wrote:
>
> Hi all, I hope the subject says it all... :-)
>
> If not, here's my problem, I really hope someone can help me:
>
> I want to backup my linux server (~10GB data) on a remote server over a
> slow line (~200 kbps). I only need a snapshot at say 1 days interval.
> The changes to the server data are relatively small so an incremental
> scheme is the way to go (and with 10GB over 200 kbps it is the only way
> :)).
>
> The problem is that the remote server is "public" available, so I need
> to encrypt the data somehow. Does anyone have any good ideas to how I
> can accomplish this?

Well, this surely sounds like an interesting problem. I don't
have a complete solution, but maybee you just need some ideas.
First of all you should probably not just use encryption, but
also use signatures, so you can verify that there has not been
tampered with files when you eventually download them.

Partial updates does not work well together with secure
encryption modes, but there are ways to cope with that. First
of all you should have some idea about what granularity you
need. Do you need to take advantage of large chunks of
unmodified data in files where a few bytes has been changed?
Or is it ok to upload the entire file if just a few bytes has
been changed?

What kind of security do you need, how many informations would
you be willing to reveal? May anybody know:
- Filenames
- Filesizes
- Number of files
- Which patterns your updates follows

How much free space do you have on the trusted server? 

-- 
Kasper Dupont -- der bruger for meget tid på usenet.
For sending spam use mailto:razor-report@daimi.au.dk

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