[geeks] Cheap/reliable backup?

[microcode at zoho.com]

On Tue, Dec 03, 2013 at 02:36:17AM -0500, Mouse wrote:
> > One thing is for sure, incremental backups based on an encrypted
> > whole-drive don't make sense.
> 
> Sure they do.  You just need to use a random-access encryption system.
> A number of them have been designed, most of them specifically for disk
> encryption AIUI.

Not that it means anything, but this is the first I've heard of it. And if
it wasn't you saying it, I wouldn't even bother trying to look it up.

>  (At its simplest, consider a block cipher whose block size equals your
> disk sector size, used in ECB mode.

I understand that was just an example, but there aren't any known block
ciphers with a 512 bit block size AFAIK. I think biggest available is 128.
I haven't followed the ECC stuff. Ok, so 4 ciphertext blocks for every disk
block. Hmmm. What did we really accomplish? We still can't do an incremental
backup of a file, only of an entire disk image or partition. Which might be
ok, but:

If you're going to work with encrypted incremental backups, it really seems
like it has to be on the file level to work with the copy tools that exist.
I'm sure you could write a script or program to manage disk blocks in an
rsync-ish way and do that, but I'm not sure how flexible that is since the
receiver has to have the same size and type file system as the sender which
is ok but not as useful as it could be. If you do things at the file level
as we do today then the backup host doesn't have to have anything in common
with the source except that it can store data. Bottom line it would be ok
for remote mirroring securely but not for a flexible incremental backup
scheme as we normally think of it. So I personally don't see a benefit, and
I think it's even less useful than what we already have.

When I have the time I'll try to look into what you mentioned at the
top. Post references/pointers if you can, please.

Thanks.

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