Re: key usage - key encipherment or data encipherment

[Arshad Noor <arshad.noor@xxxxxxxxxxxxxx>]

I am afraid, this still does not provide sufficient clarity.

Some questions that I cannot answer, based on reading the text
below (although I know the answers from practice) are:

1) Whose private key am I encrypting with the public key?  Mine?
   Hopefully not, because if this were the only copy of my private
   key, what am I going to use to decrypt the cipher-text with?
   While this may appear as a ridiculous notion, the point is that
   the text does not clarify this question.

2) What if I'm not using the certificate for key transport?  I may
   have issued a certificate to a database that generates symmetric
   keys to encrypt database content, and then stores the encrypted
   symmetric key within the same database with the cipher-text. I'm
   not transporting the symmetric key anywhere, so should I be using
   the keyEncipherment bit or the dataEncirpherment bit?

In my opinion, the confusion arises because the two bits perform
the same function: encipherment (as Simon McMahon pointed out in
an earlier posting), but for different purposes.

There is a certain simplicity to having just one encipherment bit,
letting applications decide what they want to encrypt with the
certificate's public-key and letting them codify it in *their*
protocols - as S/MIME does - or through EKU's.

Arshad Noor
StrongAuth, Inc.


Russ Housley wrote:
> There has been a whole lot of discussion about these paragraphs.  Since 
> some of the discussion has not been CCed to the PKIX mail list, I am 
> posting the resulting words.
>
>      The keyEncipherment bit is asserted when the subject public key is
>      used for enciphering private or secret keys, i.e., for key transport.
>      For example, this bit shall be set when a RSA public key is to be
>      used for encrypting a symmetric content-decryption key or an
>      asymmetric private key.
>
>     The dataEncipherment bit is asserted when the subject public key
>     is used for directly enciphering raw user data without the use of
>     an intermediate symmetric cipher. Note that the use of this
>     bit is extremely uncommon; almost all applications use
>     key transport or key agreement to establish a symmetric key.
>
> I hope we a re close to closure on this one....
>
> Russ