RE: SNI Extension for Alt-Svc

Nope, that’s the discussion in Security Considerations, basically.

It’s the same problem that HSTS and HPKP have by themselves – you have to connect to the site at least once to learn how you should have connected to the site.  Secondary Certs means a client that knows two domains are collocated could do this already.  This allows the server to use Alt-Svc to recommend a public-facing domain for the client to use, and requires less initiative from the client.  But you need a bootstrap either way.

Alt-Svc in DNS keeps coming up and would enable the bootstrapping, if you’re willing to pay the latency cost on browsing or race the resolutions.  However (as SC notes), that would allow a crawler to build a map of “hidden” domains behind the public-facing one by making DNS queries, so pick your poison carefully.

From: Martin Thomson [mailto:martin.thomson@gmail.com]
Sent: Thursday, November 30, 2017 8:23 PM
To: Mike Bishop <mbishop@evequefou.be>
Cc: Lucas Pardue <Lucas.Pardue@bbc.co.uk>; Mark Nottingham <mnot@mnot.net>; HTTP Working Group <ietf-http-wg@w3.org>; Patrick McManus <mcmanus@ducksong.com>
Subject: Re: SNI Extension for Alt-Svc

One thought that has been bugging me.  This doesn't seem to do anything for the bootstrapping scenario.  At least, not any more than the secondary certs on its own does.  Was I missing something?

On Fri, Dec 1, 2017 at 11:26 AM, Martin Thomson <martin.thomson@gmail.com<mailto:martin.thomson@gmail.com>> wrote:
Hi Mike,

Interesting idea.

How would you imagine this interacting with a client's TLS session cache?  Specifying unique SNI values that contain encrypted information is interesting, but you want to ensure that the TLS session cache for the hostname is not used or you could get linkability based on the value of a session ID or session ticket.

Also, I think that it would be good to have some sort of commitment to TLS 1.3 support.  Then you could rely on the server certificate being protected.  I don't want to have to rely on secondary certificates and the associated delays.  This seems like it could be a reasonable alternative to the secondary certificates work.


On Fri, Dec 1, 2017 at 4:56 AM, Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>> wrote:

I was already planning to spin up a thread on that draft today, so thanks for deciding what I'm doing next today!  😉  Forking a separate thread.



WG, https://tools.ietf.org/html/draft-bishop-httpbis-sni-altsvc-00 proposes a new parameter for Alt-Svc suggesting that a client use a different (presumably generic) hostname in the TLS SNI extension, and instead gain Alt-Svc "reasonable assurances" by requesting the origin's certificate via Secondary Certificates (which is currently under Call for Adoption).  It gives a solution, albeit HTTP-specific, to SNI privacy by providing a discoverability path for which generic hostname can be used to reach a more sensitive origin under encryption.



As to the frame reference, I intentionally didn't reference which protocol, in part because Alt-Svc itself says it can be carried by various mechanisms and the definition of an Alt-Svc extension doesn't need to get into that layer.  The Alt-Svc frame for HTTP/QUIC is specified by https://tools.ietf.org/html/draft-bishop-httpbis-altsvc-quic-00.  While frames are present in both HTTP/2 and HTTP/QUIC, I don't think that makes frames a generic HTTP concept -- it's a property of certain mappings, and specified individually in each of them.



-----Original Message-----
From: Lucas Pardue [mailto:Lucas.Pardue@bbc.co.uk<mailto:Lucas.Pardue@bbc.co.uk>]
Sent: Thursday, November 30, 2017 2:13 AM
To: Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>; ilariliusvaara@welho.com<mailto:ilariliusvaara@welho.com>
Cc: Mark Nottingham <mnot@mnot.net<mailto:mnot@mnot.net>>; HTTP Working Group <ietf-http-wg@w3.org<mailto:ietf-http-wg@w3.org>>; Patrick McManus <mcmanus@ducksong.com<mailto:mcmanus@ducksong.com>>
Subject: RE: DRAFT: more details for HTTPtre



Hi Mike,



The connection coalescing case is interesting as it's not currently described in HTTP/QUIC. Presumably by oversight or time constraint rather than intent. (We've got a ticket open tracking that one.)



Changing track, I've just seen your SNI I-D

https://tools.ietf.org/html/draft-bishop-httpbis-sni-altsvc-00




References to Frames don't state a specific mapping (HTTP/2 or HTTP/QUIC). Reading between the lines this seems intentional, which got me thinking that also Frames could be described as a new HTTP semantic for binary-capable wire formats.



Lucas

________________________________________

From: Mike Bishop [mbishop@evequefou.be<mailto:mbishop@evequefou.be>]

Sent: 28 November 2017 18:32

To: Lucas Pardue; ilariliusvaara@welho.com<mailto:ilariliusvaara@welho.com>

Cc: Mark Nottingham; HTTP Working Group; Patrick McManus

Subject: RE: DRAFT: more details for HTTPtre



I agree that HPACK is largely decouplable from HTTP/2, or HTTP.  The core of the protocol is a general-purpose compression algorithm for streaming key-value dictionaries, rather than straight text.  The pieces that bind it to H2 are incidental, and perhaps we could have structured it differently.



Coalescing isn't a new semantic -- each HTTP mapping defines how parallelism and connection reuse should work in that mapping.  HTTP/2 simply happens to define it more expansively than HTTP/1.1.













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