Re: Secure backup on remote untrusted server over slow line?
From: frag (frag@holmesandturner.com)Date: 06/12/02
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From: frag <frag@holmesandturner.com> Date: Wed, 12 Jun 2002 15:13:26 -0600
On Wed, 12 Jun 2002 18:42:02 GMT, "Natman" <natmanz@home.com> wrote:
>
>"Preben Bohn" <preben_bohn@yahoo.com> wrote in message
>news:3D075B5E.9C77DDBB@yahoo.com...
>> 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?
>>
>>
>> My own ideas:
>> 1) Make a secure filesystem on my own server and rsync the filesystem
>> file to the remote server. The problem with this approach is that
>> according to http://rsync.samba.org/fom-serve/cache/60.html rsync
>> requires at least 3*(the filesize)? free space on the remote server to
>> do this, and I havn't got that much... Also it seems like a waste of
>> processing power to encrypt the entire filesystem, when I only need to
>> encrypt what I send to (and store on) the remote server... This leads me
>> to option 2:
>>
>> 2) Make a program myself that reads /dev/hdXX in blocks, encrypt the
>> block, compare a checksum of this block to the corresponding checksum on
>> the remote server's block, and transfer the local block if they are
>> different. I'll probably face some problems with the disk changing while
>> reading, and such...?
>>
>> Any ideas would be highly appreciated...
>>
>> Best regards
>>
>> Preben
>
>
>I just read through this and an idea came to mind, so here it goes.
>
>To detect what has changed, you could create a 'database' of MD5sums or
>something like that. I use Tripwire, a good IDS which does something
>similar to inform me what files have changed (ie, possibly hacked by
>someone). When it comes time to backup, just run some script that makes a
>list of changes. Encrypt those files to a temporary place, send them to the
>remote end (scp?), and don't forget to update the 'database'. If free space
>is a problem locally, then just do (encrypt then send) each file one at a
>time. It doesn't matter what happens to files while the script is working,
>so there's no file locking problem. On the remote end, you would have a
>filesystem that looks exactly like yours, except each file would be
>encrypted seperatly.
>
>I believe most of this could be done with a simple script (like bash?). The
>'database' could be just a plain text file of names with MD5sums -- although
>it would be fairly large. Tripwire manages to make a database that fits on
>a floppy, most likely it uses some good compression. The encryption might
>be the hardest part, as you need to find a utility that will do whatever you
>would like. Oh, and while you're at it, why not compress (gzip) each file
>to save space.
>
>Maybe this sounds like a bit of a pain, but I think it does exactly what you
>need.
>
>Nathan
>
>
>
You may want to look into using CVS or CFengine. Not quite what they
were built for but it works...
Frag
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