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

Michael D'Errico <mike-list@pobox.com> Sat, 05 June 2010 03:31 UTC

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Date: Fri, 04 Jun 2010 20:30:52 -0700
From: Michael D'Errico <mike-list@pobox.com>
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To: "Joseph Salowey (jsalowey)" <jsalowey@cisco.com>
References: <4C092737.2060604@pobox.com> from "Michael D'Errico" at Jun 4, 10 09:17:59 am <201006041647.o54Gl4iH024692@fs4113.wdf.sap.corp> <AC1CFD94F59A264488DC2BEC3E890DE50A9EDDA1@xmb-sjc-225.amer.cisco.com>
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Cc: tls@ietf.org
Subject: Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert
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Joseph Salowey (jsalowey) wrote:
> 
> (1) "The ServerNameList MUST NOT contain more than one name of the same
> name_type. If the server understood the client hello extension, but does
> not recognize the server name, and it refuses to continue 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 the  client behavior is unpredictable.  Some clients respond by
> aborting the handshake while others allow it  to continue to certificate
> validation, which may fail as a result of a name mismatch. "

I prefer the above text, but would modify it slightly:

     If the server decides to continue the handshake, sending an
     unrecognized_name(112) alert with a warning level is NOT
     RECOMMENDED at this time due to legacy client software that
     escalates it to a fatal error.  New software is encouraged
     to treat warning alerts as informational, and not to abort
     an otherwise legitimate handshake.

Mike