Re: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt (Martin Rex) Wed, 25 September 2013 21:32 UTC

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To: "Michael D'Errico" <>
Date: Wed, 25 Sep 2013 23:32:17 +0200 (CEST)
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From: (Martin Rex)
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Subject: Re: [TLS] Comments/Questions on draft-gutmann-tls-encrypt-then-mac-00.txt
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Michael D'Errico wrote:
> >
> I think that the server MUST send a FATAL alert only if it would
> not have been willing to negotiate the lower TLS version in the
> absence of the SCSV.
> A WARNING alert from the server (or some extension_data with more
> information) lets the client decide whether to continue.  Both
> sides can keep track of these occurrences for further investigation
> by interested admins at their leisure (not via calls to the help
> desk).
> Also RFC 3546 and 4366 have been obsoleted by RFC 6066.

"Warning level alerts"?  Please don't!  As rfc6066 summarizes,
the last experiment of using warning level alerts failed badly
  -> "unpredictable client behaviour" and it is NOT RECOMMENDED.

Speaking of rfc 3546/4366/6066 "TLS Extensions":

                  If the server understood the ClientHello extension but
   does not recognize the server name, the server SHOULD take one of two
   actions: either abort the handshake by sending a fatal-level
   unrecognized_name(112) alert or continue the handshake.  It is NOT
   RECOMMENDED to send a warning-level unrecognized_name(112) alert,
   because the client's behavior in response to warning-level alerts is