Re: [TLS] TLS1.2 vs TLS1.0

[Eric Rescorla <[e-mail]>]

On Wed, May 22, 2013 at 5:51 PM, Martin Rex <[e-mail]> wrote:

> Eric Rescorla wrote:
> > Martin Rex <[e-mail]> wrote:
> > >
> > > Paterson, Kenny wrote:
> > > >
> > > > True. Though the spec for DTLS does allow DTLS implementations to
> > > > terminate a connection in the event of errors.
> > > >
> > > > It's just that most (all?) implementations don't.
> > >
> > > Now that you mention it, I hadn't noticed that DTLS gives actual two
> > > _different_ guidances (MAY abort on MAC error and MUST discard records
> > > with MAC error are mutually exclusive)
> > >
> > > http://tools.ietf.org/html/rfc4347#section-4.1.2.1
> > >
> > >    4.1.2.1  MAC  (last paragraph):
> > >
> > >    In general, DTLS implementations SHOULD silently discard data with
> > >    bad MACs.  If a DTLS implementation chooses to generate an alert
> when
> > >    it receives a message with an invalid MAC, it MUST generate
> > >    bad_record_mac alert with level fatal and terminate its connection
> > >    state.
> > >
> > > http://tools.ietf.org/html/rfc4347#section-4.1.2.5
> > >
> > >    4.1.2.5  Anti-replay  (last paragraph):
> > >
> > >    If the received record falls within the window and is new, or if the
> > >    packet is to the right of the window, then the receiver proceeds to
> > >    MAC verification.  If the MAC validation fails, the receiver MUST
> > >    discard the received record as invalid.  The receive window is
> > >    updated only if the MAC verification succeeds.
> > >
> >
> > Hmm.... I'm not sure these are contradictory.
> >
> > If you get a packet with a MAC error you MUST discard the packet (i.e.,
> > not process it.) You may either *silently* discard it (i.e.., proceed as
> if
> > you had not received it) or terminate the connection with an alert.
>
> Silently discarding it     = proceed as if you had not received it
>
> non-silently discarding it = log an error and proceed as if you had not
>                              not received it
>
> Terminating the connection with an alert means "processing it".
>

Unsurprisingly, I don't agree with this interpretation.

-Ekr