Ubuntu to store copies of all users' address books

Yes! That's why some firms have some indian people tapping everything in again... because that's cheeper

Not really, I'm sure many head hunters would love to have my address book which is full of specific targets, mostly of colleagues and friends with same technical/career orientation.

To me, targeted advertising is signal out of the random advertising noise...

if someone is after you specifically, _anything_ you do can be significant.

however, if someone is not after you specifically, but is just after things that they can sell, it becomes much easier to have reasonable defenses

"I don't have to outrun the bear, I just have to outrun you"

with "you" being enough other users that the bad guys don't get around to bothering with me.

yes, this is security by obscurity, and if someone decides to go after you it doesn't help much, but the reality is that for the vast majority of people this really is good enough.

For important things I write down my passwords and put them in my wallet.
Then I also save another copy somewhere else.

The choice is simple really.

Do you want to keep track of a password..
or depend on the security of every machine in Canonical, every workstation
in the data center that people come into contact with that people use to
access administrative portions of the "cloud"? Do want to trust the
security of every machine on the cloud? Do you want to trust every
employee, every administrator, every janitor that access to the machines
that house your data?

All in all it is a massive undertaking trying to keep data safe and
security for what will be practically forever if you take the approach that
users should take no responsibility for their data!

And it's hugely expensive undertaking, to boot. It is virtually impossible
to do in correct manner if you think about it.

Meanwhile if your job is to handle already encrypted data then it is much
simpler. You could post your customer's data to craigslist and not have to
worry about it.

It is not difficult to print out copies of your keys into ascii armor
format and put a hard copy in a secure place. People do that shit all the
time with all sorts of documents. They rent out lock boxes in banks, go and
get fire-proof safes at Walmart for 50 bucks, and all sorts of stuff like
that.

(and, frankly, the notion that you should never write down your passwords
or create hard copies of your keys is one of the worst pieces of security
"common sense" I have had the misfortune to run into over and over again.)

If you value your data and want to be able to use Ubuntu's cloud service
for anything other then a toy or a cheap way to sync address books then
client-side encryption is just the obvious way to go from my perspective.
I could be wrong, but it makes sense to me.

If the encryption key is relatively 'bare' (i.e. it's not made clear in the keyfile what service's data it's encrypting), just keep the encryption key on a USB key. Even if you drop it on a train, nobody who picks it up will have a clue what it's meant to decrypt.

(Now everyone else can tell me how stupid this idea is.)

From Colin Percival, the (Free?)BSD Security officer.

Just a happy user of the service.

(Be aware, it is a *for a fee* service, but the micropayments are truly micro!)

Try encfs + rsync. Encfs will encrypt both file content and names. (It won't hide filesizes, directory topology, permissions, and the approximate _lengths_ of filenames).

http://ubuntuforums.org/showthread.php?t=148600

Tarsnap seems like a well-engineered system, from reading the author's blog, but as far as I know
the server-side code is proprietary. The Tahoe-LAFS project (I'm a contributor) has excellent
encryption and erasure-coding features and if you like duplicity you can use Tahoe-LAFS as a
backend for duplicity. Also Tahoe-LAFS comes with its own integrated backup system which has
different trade-offs than the duplicity backend. (Duplicity does deltas for you, but you can't view or
download your files without going through duplicity. The Tahoe-LAFS integrated backup doesn't do
deltas, but it stores the files in a time-machine-style layout which you can browse and download
through the web.)

The meet in the middle attack reduces the time from 2^(2n) to 2^(n+1). This is why 3DES (even with 168 bits of keying) only effectively gives 112 bits of security. That's why I didn't propose 4DES, which wouldn't have any improvement in security over 3DES. However, my proposed 6DES would give 168 bits of security, or 8DES sould give 224, etc. 6DES has the advantage that you can use an existing 3DES implementation twice.

However, that's just the time complexity. The meet in the middle attack also requires storage for 2^n blocks, which is obviously not available for n=112, let alone larger values of n.

> Just using the same encryption algorithm twice with two different keys of
> size N does not increase the exhaustive search time from 2^n to 2^2n,
> thanks to meet-in-the-middle attacks, which reduce the time to 4^n.

I think there is a mistake somewhere in there, because 2^(2n) = (2^2)^n = 4^n.