Re: [sfc] Roman Danyliw's Discuss on draft-ietf-sfc-nsh-integrity-06: (with DISCUSS and COMMENT)

[tirumal reddy <[e-mail]>]

On Fri, 16 Jul 2021 at 01:06, Benjamin Kaduk <[e-mail]> wrote:

> On Wed, Jul 14, 2021 at 02:57:42PM +0530, tirumal reddy wrote:
> > Hi Roman,
> >
> > Please see inline
> >
> > On Wed, 14 Jul 2021 at 00:33, Roman Danyliw via Datatracker <
> > [e-mail]> wrote:
> >
> [...]
> > >
> > > -- The text would benefit from a description on how to serialize the
> > > packet for
> > > hashing.  For example, Figure 6 and 7 are helpful logical descriptions
> of
> > > the
> > > integrity scope.  However, the MAC field itself is depicted as part of
> the
> > > what
> > > should get hashed.  Should that field be zeroed out? Removed ?
> > >
> >
> > Yes, we will update text as follows:
> >
> > The NSH imposer sets the MAC field to zero and then computes the message
> > integrity for the target NSH data (depending on the integrity protection
> > scope discussed in Section 5) using MAC_KEY and HMAC algorithm. It
> inserts
> > the computed digest in the MAC field in the "MAC and Encrypted Metadata"
> > Context Header.
>
> It's probably also worth updating the description of the verification
> procedures to match; we typically see these done in tandem.
>

Yes, we will update Section 7.5 as follows:

After storing the value of the MAC field in the "MAC and Encrypted
Metadata" Context Header, the SFC data plane element fills the MAC field
with zeros.  Then, the SFC data plane element generates the message
integrity
for the target NSH data (depending on the integrity protection scope
discussed in Section 5) using MAC_KEY and HMAC algorithm.  If the value of
the newly generated digest is identical to the stored one, the SFC data
plane element is certain that the NSH data has not been tampered and
validation is therefore successful. Otherwise, the NSH packet MUST be
discarded. The comparison of the computed HMAC value to the store value MUST
be done in a constant-time manner to thwart timing attacks.

-Tiru

>
>
> -Ben
>