Re: 2.6.3-mm1

[Bill Davidsen]

Christophe Saout wrote:
> Am Mi, den 18.02.2004 schrieb Brandon Low um 21:52:
>
>
> > I am just reading up on dm now, but correct me if I am wrong, I will
> > need to do losetup, dmcreate, mount in that order in order to use
> > dmcrypt on loop where with cryptoloop, I could just do "mount"... there
> > must be an easier way to handle this!
>
>
> You don't need to know everything about dm to set up encrypted devices.
>
> Basically dmsetup is something like losetup, only that it's much more
> flexible.
>
> 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.
>
> mount -o loop is basically a hack. mount uses parts of losetup to do an
> ioctl. The encryption support as mount argument is an additional patch.
> Even worse, some do passphrase hashing, some don't... it works but it's
> not a very clean solution either.
>
> BTW: dmsetup is NOT a big program. It has two parts: a libdevmapper.so
> in /lib and the dmsetup binary itself. Every part is 16k in size (if
> compiled statically into one binary it's just 27k), and it's still
> linked against glibc. If linked against dietlibc or klibc it would be
> even smaller. Nobody needs LVM tools or something. It's just a small
> client for the dm ioctl, just like losetup is a client for the loop
> ioctl.
>
> 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.
>
> So, you see. NO NEED TO PANIC. Cryptoloop won't disappear over night.
> There will be some nice to user interface. At the moment dm-crypt is
> only a *kernel implementation* and not meant to be used by every end
> user immediately. Nobody will force you to drop cryptoloop until there
> is a clean solution for everybody out there.

Could you give an example of the one line I put in /etc/fstab to replace 
the one now which includes "noauto,user" so users can mount when they 
need the secure data?

You *can* do that so you don't need to train users, give them special 
permissions, or use privileged scripts or programs, right?

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