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

"Fossati, Thomas (Nokia - GB)" <> Fri, 04 March 2016 07:19 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 07:10:06 +0000
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Subject: Re: [TLS] Accepting that other SNI name types will never work.
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Trying again...

> Hi Adam,

In CoRE we might need to allocate a new SNI NameType for non-DNS host
names [1].

Removing SNI extensibility would make it unfeasible.

Cheers, t


>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