Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert

I was about to say that ... but eventually realised I was misinterpreting the
text, so I suggest adding a clause to express the 'if-then-else' more
rigourously ie

"The ServerNameList MUST NOT contain more than one name of the same
name_type.

If the server understood the client hello extension, but
**decides not to continue because it does not recognize the server name, it
MUST send a fatal unrecognized_name(112) alert and terminate the
handshake.

**If the server understood the client hello extension but** decides to continue
the  handshake, sending a warning-level unrecognized_name(112) alert is NOT
RECOMMENDED, since existing  client behavior is unpredictable.

...."

which also makes it clear we are not covering the case of client hello extension
not understood.

Tom Petch

----- Original Message -----
From: "Joseph Salowey (jsalowey)" <jsalowey@cisco.com>
To: <mrex@sap.com>
Cc: <tls@ietf.org>
Sent: Tuesday, June 08, 2010 1:10 AM
Subject: Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert

> OK with me, so we have:
>
> "The ServerNameList MUST NOT contain more than one name of the same
> name_type. If the server understood the client hello extension, but
> refuses to continue because it does not recognize the server name, it
> MUST send a fatal unrecognized_name(112) alert and terminate the
> handshake.  If the server decides to continue the  handshake, sending a
> warning-level unrecognized_name(112) alert is NOT RECOMMENDED, since
> existing  client behavior is unpredictable. A TLS client implementation
> that receives a warning-level unrecognized_name(112) alert SHOULD ignore
> this alert and continue the TLS handshake.  If there is a mismatch
> between the server name used by the client application and the server
> name of the default credential chosen by the server, this mismatch will
> become apparent when the client application performs the server endpoint
> identification, at which point the client application will have to
> decide whether to proceed with the communication.  TLS implementations
> are encouraged to make information available to application callers
> about warning-level alerts that were received during a TLS handshake.
> Such information can be useful for diagnostic purposes. "
>
>
>
> > -----Original Message-----
> > From: Martin Rex [mailto:mrex@sap.com]
> > Sent: Monday, June 07, 2010 3:04 PM
> > To: Joseph Salowey (jsalowey)
> > Cc: tls@ietf.org
> > Subject: Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert
> >
> > Joseph Salowey wrote:
> > >
> > > OK, here is some new suggested text.  Let me know if you can live
> with
> > > this.
> > >
> > > "The ServerNameList MUST NOT contain more than one name of the same
> > > name_type. If the server understood the client hello extension, but
> > > refuses to continue because it does not recognize the server name,
> it
> > > MUST send a fatal unrecognized_name(112) alert and terminate the
> > > handshake.  If the server decides to continue the  handshake,
> sending a
> > > unrecognized_name(112) alert with a warning level is NOT
> RECOMMENDED,
> > > since existing  client behavior is unpredictable.  A client that
> > > receives a warning-level unrecognized_name(112) alert SHOULD ignore
> this
> > > alert and continue the TLS handshake, which may fail as a result of
> a
> > > name mismatch.  The warning MAY be logged as part of diagnostic
> > > information recorded for a failed handshake."
> >
> >
> > I am fine with what I think is the intention of this wording,
> > but I would actually appreciate to be more specific about what
> > "may fail as a result of a name mismatch" applies to exactly.
> >
> >                                                      A TLS client
> >   implementation that receives a warning-level unrecognized_name(112)
> >   alert SHOULD ignore this alert and continue the TLS handshake.
> >   If there is a mismatch between the server name used by the client
> >   application and the server name of the default credential chosen
> >   by the server, this mismatch will become apparent when the client
> >   application performs the server endpoint identification, at which
> >   point the client application will have to decide wether to proceed
> >   with the communication.  TLS implementations are encouraged to
> >   make information available to application callers about
> warning-level
> >   alerts that were received during a TLS handshake. Such information
> >   can be useful for diagnostic purposes.
> >
> >
> > -Martin
>
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