Re: [TLS] Accepting that other SNI name types will never work.

"Fossati, Thomas (Nokia - GB)" <> Fri, 04 March 2016 07:15 UTC

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From: "Fossati, Thomas (Nokia - GB)" <>
To: Adam Langley <>, "" <>
Thread-Topic: [TLS] Accepting that other SNI name types will never work.
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Date: Fri, 4 Mar 2016 07:06:09 +0000
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Subject: Re: [TLS] Accepting that other SNI name types will never work.
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Hi Adam,

On 03/03/2016 18:49, "TLS on behalf of Adam Langley" <
on behalf of> wrote:
>The Server Name Indication (SNI) extension in TLS has a provision to
>provide names other than host names[1]. None have even been defined to
>my knowledge, but it's there.
>OpenSSL (and possibly others) have had a long-standing bug[2] (fixed
>in master) that means that different types of names will cause an
>error. To be clear: I live in a glass house and am not throwing
>stones; these things happen. However, it means that a huge fraction of
>the TLS deployment will not be able to accept a different name type
>should one ever be defined. (This issue might have been caused by the
>fact that the original[3] spec didn't define the extension in such a
>way that unknown name types could be skipped over.)
>Therefore we (i.e. BoringSSL, and thus Google) are proposing to give
>up on this and implement our parser such that the SNI extension is
>only allowed to contain a single host name value. (This is compatible
>with all known clients.) We're assuming that since this is already the
>de-facto reality that there will be little objection. I'm sending this
>mostly to record the fact so that, if someone tries to define a new
>name type in the future, they won't waste their time.
>If the community wishes to indicate a different type of name in the
>future, a new extension can be defined. This is already effectively
>the case because we wouldn't fight this level of incompatibility when
>there's any other option.
>(I think the lesson here is that protocols should have a single joint,
>and that it should be kept well oiled. For TLS, that means that
>extensions should have minimal extensionality in themselves and that
>we should generally rely on the main extensions mechanism for these
>sorts of things.)
>­ note that the data pointer is not updated.
>Adam Langley
>TLS mailing list