On Mon, Jul 29, 2019 at 8:18 PM Sehrope Sarkuni <sehrope@jackdb.com> wrote:
>
> On Mon, Jul 29, 2019 at 6:42 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > > An argument could be made to push that problem upstream, i.e. let the
> > > supplier of the passphrase deal with the indirection. You would still
> > > need to verify the supplied passphrase/key is correct via something
> > > like authenticating against a stored MAC.
> >
> > So do we need the key for MAC of passphrase/key in order to verify?
>
> Yes. Any 128 or 256-bit value is a valid AES key and any 16-byte input
> can be "decrypted" with it in both CTR and CBC mode, you'll just end
> up with garbage data if the key does not match. Verification of the
> key prior to usage (i.e. starting DB and encrypting/decrypting data)
> is a must as otherwise you'll end up with all kinds of corruption or
> data loss.
>
Do you mean that we encrypt and store a 16 byte input with the correct
key to the disk, and then decrypt it with the user supplied key and
compare the result to the input data?
> From a single user supplied passphrase you would derive the MDEK and
> compute a MAC (either using the same key or via a separate derived
> MDEK-MAC key). If the computed MAC matches against the previously
> stored value then you know the MDEK is correct as well.
You meant KEK, not MDEK?
Regards,
--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
