Re: 2.6.3-mm1

Christophe Saout
2004-02-19T12:39:15Z

Am Do, den 19.02.2004 schrieb Brandon Low um 01:33:

> > To set up a device basically:
> >
> > echo 0 `blockdev --getsize /dev/bla` crypt <cipher> <key> 0 /dev/bla 0 |
> > dmsetup create <newname>
> >
> > is enough. And it's just temporary, because no special tool has been
> > written yet. dmsetup is the most low-level dm tool, mostly for
> > developers. I've written a shell script named cryptsetup for the
> > meantime, it asks for a passphrase and does all the magic you need.
> >
> > "cryptsetup create test /dev/hda5" will ask for a passphrase and set up
> > /dev/mapper/test. Voila. "cryptsetup remove test" removes it and
> > "cryptsetup status test" shows some status information.
> >
> What I can't figure out yet is how to do that easily for a loopback...
> use losetup first, and then cryptsetup? I guess that's ok, just more
> steps than I would prefer.

Yes. Block->File and Block->Crypto->Block are two different things and
should be separated out. But it would be an easy one to make cryptsetup
also call losetup if your specified backend happens to be a file. Like
mount -o loop does. The only thing I'm not sure about: How would it know
when to remove the loop device on "cryptsetup remove" and when now.
mount stores it in the mtab.

I've got some free time, I think I'm going to rewrite cryptsetup as a
small C program today.

> I was under the mistaken impression that I would need lvmtools as well
> in order to use dmcrypt... cool.

Yes, there's some FUD going around...

> > There are some plans to write a unified plugin based key management
> > tool. You might want to have your key stored on a USB stick. Or
> > encrypted in the first sector of your device and you want to unlock it
> > using a password (so you can change your password without needing to
> > reencrypt your data). This would be much more flexible than most of the
> > crap floating around.
>
> That sounds very cool, saw mention of putting it in the first part of
> the device elsethread.

Yes, for example.

> Ok ok, I'll quit panicking... this just makes it hard to decide which to
> use now as I'm preparing to deploy soon... If I use cryptoloop, it is
> now guaranteed to be obsolete soon, but if I use dmcrypt, it is more
> work right now, but more forward looking...
>
> Can you point me to some useful readings related to dmcrypt,
> devicemapper for loopback, etc.? Thanks!

For dm-crypt I've set up a small page:
http://www.saout.de/misc/dm-crypt/

For device-mapper and loopback there's nothing. The loop device provides
block devices, device-mapper can use them. Nothing special here.