Re: key usage - key encipherment or data encipherment

["Wen-Cheng Wang" <wcwang@xxxxxxxxxx>]

Russ,

Yes, RFC 3280 is quite clear for that. However, I worried
that the discussions of this thread might mislead the
participants into believing that the two bits are mutually
exclusive. Therefore, I simply want to remind the
participants of this thread the fact that the keyEncipherment
bit and dataEncipherment bit can work well togethor.

Wen-Cheng Wang


----- Original Message ----- 
From: "Russ Housley" <housley@xxxxxxxxxxxx>
To: "Wen-Cheng Wang" <wcwang@xxxxxxxxxx>
Cc: <ietf-pkix@xxxxxxxx>
Sent: Wednesday, May 11, 2005 11:40 PM
Subject: Re: key usage - key encipherment or data encipherment


> I believe that RFC 3280 is quite clear that more than one of these bits can 
> be set.  It says:
>
>    This profile does not restrict the combinations of bits that may be
>    set in an instantiation of the keyUsage extension.  However,
>    appropriate values for keyUsage extensions for particular algorithms
>    are specified in [PKIXALGS].
>
> Russ
>
> At 03:47 AM 5/11/2005, Wen-Cheng Wang wrote:
>
>
> > Peter Gutmann <pgut001@xxxxxxxxxxxxxxxxx> wrote:
> > > Andrew Sciberras <andrewsciberras@xxxxxxxxx> writes:
> > >
> > > >     The keyEncipherment bit is asserted when the subject public key is
> > > >      used for key transport.  For example, when an RSA key is to be
> > > >      used for key management, then this bit shall asserted.
> > > >
> > > >      The dataEncipherment bit is asserted when the subject public key
> > > >      is used for enciphering user data, other than cryptographic keys.
> > > Quoting that won't help (I've seen this sort of thing before) because as far
> > > as the user is concerned what's being encrypted is data, so the valid bit to
> > > use is dataEncipherment (quite logical to them).  What might help is to make
> > > this more explicit in the text:
> > >  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.  This bit MUST NOT be set when the intention is to
> > >  encipher intermediate cryptographic keys rather than raw user data.
> > It is better to clarify that it is legitimate to assert both the 
> > keyEncipherment bit
> > and the dataEncipherment bit in one certificate. In that case, it means 
> > that the
> > key (e.g., RSA key) may be used for enciphering intermediate cryptographic
> > keys or directly enciphering raw user data (e.g., user password).
> >
> > Wen-Cheng Wang