Re: NT 5.0 and EFS -- A victory for widespread use of crypto?

[Steve Dunlop <nospam@bitstream.net>]

landon dyer wrote:

> At 06:06 PM 10/7/98 -0500, you wrote:
> >
> >Does anyone have any opinions on the encrypting file
> >system (EFS) that is supposed to ship with NT 5.0?
>
>
>   "...NTFS has built-in recovery support so that the encrypted
>    data can be accessed.  In fact, NTFS won't allow files to be
>    encrypted unless the system is configured to have at least
>    one recovery key.  For a domain environment, the recovery keys
>    are defined at the domain controller and are enforced on all
>    machines within the domain...."
>
>   i'll definitely have to play with this one -- wh'appens if you add
> a machine to a domain, encrypt some files, then remove the machine
> from the domain?  can the admin of the domain recover all files
> you encrypt from that point on?  and so on...

MSJ conflicts with the MS white paper in that, according to MS,you can
explicitly turn off key recovery at the domain level.  For
workstations not a part of a domain, key recovery can be turned
off at the local administrator level.

The domain setting overrides the local administrator setting
as long as the workstation is a member of a domain. So the
answer to your question, apparently, depends on the local
administrator's settings for the encryption policy.

>   "...For home users, NTFS automatically generates recovery keys
>    and saves them as machine keys.  You can then use command-line
>    tools to recover data from an administrator's account."
>
>   if i were looking for a point of attack, i'd start with the
> low-level key management here...
>

Their summary is somewhat simplified.  The key managementhas several
alternatives with the usual tradeoffs between
security and convenience.  The private key for recovery can
be stored on a floppy, encrypted using a passphrase, or
for that matter can be destroyed.

>   another interesting thing to try: install NT on a workstation,
> encrypt a removable disk, then reinstall NT on that workstation
> again -- have you defeated key recovery for that disk?  (since the
> machine keys for the first install of NT are presumably gone...)
>
> -landon (re-lurking)

Yes, if you are using self-signed certificates they are
generated randomly during each install.

--
Steve Dunlop
letters: "dunlop" at "bitstream" dot "net"
http://www2.bitstream.net/~dunlop