[Techtalk] Using rsync to remote backup encrypted files?

[Terri Oda]

  I'd be awfully suspicious about using any service that claims to  
have gotten around this problem.  Basically, the best encryption gives  
away as little info as possible, so changing one byte in the original  
has to change a bunch of things (possibly everything) in the encrypted  
version, making rsync less useful.  Working around that likely means  
giving away additional information, so you'd be weakening the security  
guarantees provided by the encryption.  You could get some traction  
from a streaming block cipher if you're only changing the end of the  
file, maybe, but assuming you're just using gpg, you're probably out  
of luck.

If you're working with all servers you control, you can decrypt-rsync- 
reencrypt, but that means (at least) two machines would have access to  
the secret keys, which may or may not be desirable depending on your  
setup.

On 2008-Oct-6, at 3:22 PM, Kelly Jones wrote:

> I use rsync to backup files remotely.
>
> This works great if they're unencrypted: a small change in a large
> file requires very little bandwidth to sync.
>
> But if I encrypt files, this no longer works: a small change in a
> large file could result in a completely different file, so I lose the
> benefit of rsync.
>
> How do people workaround this? I know online backup companies (like
> mozy.com) must solve this problem somehow?
>
> -- 
> We're just a Bunch Of Regular Guys, a collective group that's trying
> to understand and assimilate technology. We feel that resistance to
> new ideas and technology is unwise and ultimately futile.
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