[Wolves] Tinkle tinkle little disk...

Stuart Langridge sil at kryogenix.org
Thu Jan 3 19:11:42 GMT 2008

> >read them. That's all. There are three problems with this, none of
> >which I have a clear idea how to solve. They are:
> >  rsyncness
> >  encryption key loss
> >  bandwidth
> You could break the file up into blocks (say 4KB each) then calculate the difference between each block and the previous back up of that block, then if theres any changes, encrypt the diff, compress it and send it over.

...also known as: reinvent rsync. You're right, though :-)

To be honest, it's probably better to do what Peter suggested, and
break the files up into blocks, and encrypt each block, then just ship
changed blocks. This does rely on a small change in a large file not
having effects throughout the file, but that's relatively unlikely.

> You actually dont need to reconstruct the file from the diffs untill you restore it so all the remote site ends up storing is encryted compressed messages that say "at 23:00 on 29thFeb in file X in the 23rd 4k block changed the seventh byte from a to e". To restore you get all of the patch files and rerun them in time order.

Erf. Then reassembling your backups becomes a horrible jigsaw puzzle,
I think, which is made a lot more complex by how some of your backup
nodes likely won't be on the network :)

> The encryption key problem is more of a pain, probably the best way I can think of is to use an encryption system that always generates the same key from the same passphrase. It would make Bruce Schneier cry but your dad would only need to remember his phrase (or even better "its the first line of my favourite book"). Not exactly military grade security but does it need to be? and even if someone cracks it they cant *change* the data because theres several copies distributed around to compare.

Yeah, so I gotta ask the user for a passphrase when they first use the
system. Still, that's the flaw with encrypting it, I suppose...

New Year's Day --
everything is in blossom!
I feel about average.
   -- Kobayashi Issa

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