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Cody Dunne wrote:
> I recently ran into a paper on convergent encryption, which is a way of 
> encrypting file blocks by their hashes. The hashes (keys) are stored 
> with the blocks, encrypted with the public key of any authorized 
> readers. This allows a server to pool identical files, as they end up 
> having identical encrypted blocks. This would allow BackupPC to still 
> work as it does now. Naturally, file size, location, quantity, etc are 
> visible but the contents wouldn't be.
> 
> I'm not sure if this has been suggested before, but a brief peruse of 
> the archives didn't turn anything up. It seems like the arguments 
> against encryption in the past found the pooling issue insurmountable.

I suppose there are a number of issues which should be solved by any
encryption/backup solution, but which issues each person needs solved
are different.

1) In some cases, the idea is to stop any third party that happens to
break into the backup server from retrieving the data.
2) In other cases, you also want to prevent the admin of the backup
server from being able to access the un-encrypted data
3) I'm sure there are other scenarios as well, but those are best
resolved with a VPN/similar solution.

To solve (1) there are probably a number of solutions from using an
encrypted filesystem, or similar, though I'm not sure how useful that is
when you need to leave the filesystem mounted 100% of the time so that
backups can occur when needed. Same applies for auto-mounting the
filesystem just before a backup, if the system can automount, then so
could an attacker...

To solve (2) there are also a number of possible solutions, one of which
was mentioned on this list recently (rsync + encryption) which involved
creating an encrypted directory structure (copy of the data) and then
using the standard rsync to backup this encrypted structure.

The ideal solution (from my perspective :) ) would be to have a custom
open source'backuppc client' which can be installed on any linux or
windows system, which supports rsync-like backups, with optional
encryption prior to sending the data. This encryption will probably
destroy the concept of pooling (unless every encryption key is the same
on all clients), but it does make use of the other 90% of what backuppc
provides (scheduling, interface, etc)

Of course, the 'custom open source client' would also solve a number of
other issues such as allowing the client to select which folders/files
to include/exclude in the backup etc....

Regards,
Adam

- --
Adam Goryachev
Website Managers
www.websitemanagers.com.au
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