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Joseph Salowey (jsalowey) wrote:
> 
> "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.

OK.

> 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.

After reading this again, I think it's missing something:  If the
server understood the extension but did not recognize the server name,
yet continues with the handshake anyway using default configuration
parameters, sending a warning-level....

Mike

> 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 or sent during a TLS handshake.  Such
> information can be useful for diagnostic purposes."
> 
>> -----Original Message-----
>> From: t.petch [mailto:ietfc@btconnect.com]
>> Sent: Tuesday, June 08, 2010 5:45 AM
>> To: Joseph Salowey (jsalowey)
>> Cc: tls@ietf.org
>> Subject: 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
>>> _______________________________________________
>>> TLS mailing list
>>> TLS@ietf.org
>>> https://www.ietf.org/mailman/listinfo/tls
> 
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