On Wed, Oct 03, 2018 at 07:08:41PM +0200, ro...@seffner.de wrote:
>
> Using user or session based keys suggests me no other session/user is able
> to take advantage of them. It seems to me as the following
> - permissions/ACL's controls the access rights to en-/decrypted filesystem
> objects
> - each object (file/directory) hast o be decrypted by the keyowner before
> other (permission/ACL's enabled) users can access encrypted content
> Did I understand it right now?
That's about how things work right now, but the truer answer is that
fscrypt was *not* designed for the use case where encrypted files
which are shared between multiple users. And the keyring
infrastructuer in the kernel doesn't have the concept of global keys
(again because it doesn't actually make that sense from a keying
perspective --- what use are keys if everyone on the system can use
them, at least in the general case)?
> My usecase is a crypted folder on an external storage shared by local and
> remote samba users. So I have to add the decryption-key to one user an link
> it to all th others.
For that use case, I'd argue that fscrypt is simply not the right
solution. What actually are you trying to protect? Since it's on a
file server, the keys have to be available any time the file server is
up. So what is your security model? Who are potential attackers, and
what capabilities do they have, and what do you hope to have the file
system encryption provide?
Using dm-crypt to encrypt the entire file system is probably a closer
match, but again, what do you hope to achieve by using encryption in
the first place? If the file server has to come up automatically
after a reboot, and the keys are located permanently on the file
server --- what point is the encryption? Especially since CIFS/SMB
doesn't have any protocol level encryption, so sending the file data
unencrypted across your network is probably a **much** bigger threat
than whatever security properties you might have for keeping the bits
on the platter encrypted (and the key permanently installed in the
server memory, if not on some server boot files).
I don't have the whole story, but from what you've told me, the
picture appears to be one of vault doors and paper maiche walls. Was
the encryption only to provide paper-level certification for
"encryption at rest" without actually trying to provide any real
security? And I don't say that as a criticism; we have security
theater every time we fly in airports; the security measures don't
really provide *real* security, but it makes the passengers feel good,
which is an important business objective for the airlines, even if it
isn't really all that security relevant. :-)
- Ted
