On Wednesday, 4 July 2018 18:54:10 CEST Eric Rescorla wrote: > On Wed, Jul 4, 2018 at 6:36 AM, Hubert Kario <hka...@redhat.com> wrote: > > On Wednesday, 4 July 2018 15:00:18 CEST Eric Rescorla wrote: > > > I think it's a close call, because the length is sort of external to the > > > language. > > > > which language? the decode_error alert description literally says "length > > of > > the message was incorrect." > > The protocol definition language.
Sorry, I really don't see it. There are multiple references to "length" in the
draft, and as far as I can tell, all are quite consistent.
> -Ekr
>
> > > That's why, for instance, NSS sends "illegal_parameter". So,
> > > absent specific text about this value, I think this is something we can
> > > leave to the implementations.
> >
> > but the text is explicit, if a message continues past message boundary,
> > the
> > correct response is decode_error. Decode_error is also consistent with the
> > way
> > above-expected length Client Hello MUST be handled.
> >
> > Just because the description of the message uses a single opaque array
> > doesn't
> > make this message syntactically any different from other Handshake
> > protocol
> > message.
> >
> > if the interpretation of "I know this _message_ _length_ is wrong because
> > of
> > some other values I negotiated before, so I'll send illegal_parameter" was
> > correct, then overflow_error, decrypt_error and probably few others would
> > also
> > need to be replaced with illegal_parameter...
> >
> > > -Ekr
> > >
> > > On Wed, Jul 4, 2018 at 2:54 AM, Hubert Kario <hka...@redhat.com> wrote:
> > > > Despite this, is it correct to terminate a connection with
> > > > "illegal_parameter"
> > > > upon receiving a Finished handshake message with a 100 byte payload?
> >
> > or a
> >
> > > > 20
> > > > byte payload? My opinion is that it is not, "decode_error" is more
> > > > specific so
> > > > it should be used instead.
> > > >
> > > >
> > > > Specification says the following on the matter:
> > > >
> > > > The draft 28 specifies the Finished message as having following
> >
> > structure:
> > > > struct {
> > > >
> > > > opaque verify_data[Hash.length];
> > > >
> > > > } Finished;
> > > >
> > > > At multiple places it also talks about handling messages that have
> >
> > sizes
> >
> > > > that
> > > > don't match their structure as requiring termination of connection
> > > > with
> > > > "decode_error".
> > > >
> > > > The generic situation in Section 6:
> > > > Peers which receive a message which
> > > > cannot be parsed according to the syntax (e.g., have a length
> > > > extending beyond the message boundary or contain an out-of-range
> > > > length) MUST terminate the connection with a "decode_error" alert.
> > > >
> > > > as description of the alert in Section 6.2:
> > > > decode_error A message could not be decoded because some field was
> > > >
> > > > out of the specified range or the length of the message was
> > > > incorrect. This alert is used for errors where the message does
> > > > not conform to the formal protocol syntax.
> > > >
> > > > In specific about Client Hello, in Section 4.1.2:
> > > > If negotiating a version of TLS prior to 1.3, a server MUST check
> > > > that the message either contains no data after
> > > > legacy_compression_methods or that it contains a valid extensions
> > > > block with no data following. If not, then it MUST abort the
> > > > handshake with a "decode_error" alert.
> > > >
> > > > And specific handling of Certificate from server in Section 4.4.2.4:
> > > > If the server supplies an empty Certificate message, the client
> > > > MUST
> > > > abort the handshake with a "decode_error" alert.
> > > >
> > > > Description of "illegal_parameter" in Section 6:
> > > > Peers which receive a message which is syntactically correct but
> > > > semantically invalid (e.g., a DHE share of p - 1, or an invalid
> >
> > enum)
> >
> > > > MUST terminate the connection with an "illegal_parameter" alert.
> > > >
> > > > Alert description in Section 6.2:
> > > > illegal_parameter A field in the handshake was incorrect or
> > > >
> > > > inconsistent with other fields. This alert is used for errors
> > > > which conform to the formal protocol syntax but are otherwise
> > > > incorrect.
> > > >
> > > > (it's also mentioned in over a dozen places in the draft)
> > > > --
> > > > Regards,
> > > > Hubert Kario
> > > > Senior Quality Engineer, QE BaseOS Security team
> > > > Web: www.cz.redhat.com
> > > > Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
> > > > _______________________________________________
> > > > TLS mailing list
> > > > TLS@ietf.org
> > > > https://www.ietf.org/mailman/listinfo/tls
> >
> > --
> > Regards,
> > Hubert Kario
> > Senior Quality Engineer, QE BaseOS Security team
> > Web: www.cz.redhat.com
> > Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
--
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
