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Re: cgd(4) ciphers
Le 02/10/13 19:18, Roland C. Dowdeswell a écrit :
The reason that we have configuration files rather than putting a
few bytes at the start of the disk is that you can keep the config
files separately from the disk in question which gives you various
advantages. E.g. you can frustrate dictionary attacks against a
lost external USB disk if your parameter file is not stored on it
but rather only on the laptop onto which it is usually plugged.
The params files also have options such as simply storing the key
for the above USB disk case or other similar cases. You can also
set it up to fetch keys from a key server via the ``shell_cmd''
key generation method for unattended booting of a server with an
encrypted disk. None of these use cases can be accomodated with
a few bytes at the start of the volume read in by the boot blocks.
Heh, I missed that one. Thanks for pointing it out :o
(And putting my tongue firmly in my cheek, you can _only_ achieve
_full_ disk encryption if you store the paramsfile on another disk
because how else would you ensure that each and every disk block
is encrypted? ;-)
Of course. The usual setup for full disk encryption is rather a small
bootloader and kernel on which we only have integrity checks (through
TPM Seal/Unseal), and if the check is successful, unlock key.
It is by no mean easy to achieve correctly and easily though (TPM
management + next-to-full-disk-encryption).
Back to being serious, we could easily support boot-block crypto
(not full disk) via various mechanisms. I haven't done it as I
have not had the need for it. If we do it, though, I would ask
that we leave the existing framework in place as I find it useful
to be able to setup things that are a little more complicated on
It all boils down to what can be done: I have no idea how much time
is needed to get a new cipher implemented within cgd(4), but the
first step is to chose one. And that does not look very trivial to
A new cipher is trivial to add. That said, what we should do is
wire it into the opencrypto(9) which will require a little work
which I haven't found time to do.
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