Re: [DNSOP] Proposal for a new record type: SNI
Ben Schwartz <bemasc@google.com> Sat, 18 February 2017 02:37 UTC
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From: Ben Schwartz <bemasc@google.com>
Date: Fri, 17 Feb 2017 21:37:36 -0500
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To: Erik Nygren <erik+ietf@nygren.org>
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Cc: dnsop@ietf.org, dkg@fifthhorseman.net
Subject: Re: [DNSOP] Proposal for a new record type: SNI
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On Fri, Feb 17, 2017 at 9:02 PM, Erik Nygren <erik+ietf@nygren.org> wrote: > I wrote a similar draft a few years ago which I've been considering > resurrecting if there is interest: > > https://tools.ietf.org/html/draft-nygren-service-bindings-00 > Thanks for pointing this out, Erik! I think a flexible binding record like B could be a great way to solve this problem and also enable clean future extensibility. With the standardization of DNS over TLS, I think your binding draft might make more sense. Maybe it's time to revisit. The major concerns I have about B as described there are latency and graceful degradation. Does this add delay to new connections? Does it break connections if the client is behind a resolver that silently drops all queries other than "A"? My impression is that, for a new record to be widely usable, both answers must be "no". My draft attempts to resolve both dilemmas by (1) getting a head start on the SYNACK and (2) specifying fallback behavior if the SNI response doesn't arrive in time, along with a strategy to minimize the impact of fallback. Maybe those ideas could be applied to some version of B. > > > One of the big challenges that at least in the web context, browsers want > to make as few DNS lookups as possible prior to making HTTP requests. > (For example, some home gateways choke if too many requests are > outstanding.) > Having to lookup both A and AAAA is already a problem. So if we're going > to add > something, ideally we'd add something that was extensible that could be > used > for multiple purposes. > > For this case, the result could be something like: > > _https._b.www.example.com IN B 2 0 www.example.com. { "alpn": "h2", "tls-sni": "SOME_TOKEN", "hsts": true } > _https._b.www.example.com IN B 1 0 www-alt.example.com. { "alpn": "quic352", "tp": 443, "tls-sni": "SOME_OTHER_TOKEN", "hsts": true } > > By adding this one single lookup, you both get to specify an alternate SNI, > be able to force HTTPS-only, and specify Alternative Services (ala rfc7838 > but allowing it to be done in DNS). Having an extensible model here also > increases > the value of a client doing the lookup as once the records exist other > optional > attributes can be added in. > > (Ignore the specific key/value pair examples in that expired I-D. They > made more > sense when some other things were being considered.) > > Based on our extensive discussions in the TLS WG over the past few years, > introducing something like this into the DNS to indicate an alternate SNI > value > (which might be one shared with many other hostnames) or telling the > client > not to send an SNI value seemed to be one of the best ways to help with > the SNI privacy problems, at least once there is a DNS privacy path. > > For example, for a cert like *.example.com (perhaps with lots of other > SANs as well) > there is no reason the client needs to send "something-potentially- > private.example.com" when sending > an SNI value of "wildcard.example.com" would do just fine. The TLS > handshake > is too late to learn this, but if we could move it into the DNS then > clients > could learn it (and potentially other useful info) before connecting. > > [I added DKG as he was a strong advocate of doing something in this space > for signalling TLS SNI omission, alteration, or aliasing in DNS records.] > > Erik > > > > > On Fri, Feb 17, 2017 at 3:49 PM, Ben Schwartz <bemasc@google.com> wrote: > >> Thanks for the input everyone! Here's an updated version with some >> clarifications based on your feedback: >> https://tools.ietf.org/html/draft-schwartz-dns-sni-02 >> >> Diff: >> https://www.ietf.org/rfcdiff?url1=draft-schwartz-dns-sni-01& >> url2=draft-schwartz-dns-sni-02 >> >> I know this approach is controversial, so I'm also very curious to hear >> any suggestions of other ways that we could fix this privacy leak without >> slowing down everyone's connections. As a friend put it: if everyone can >> see you're reading justinbieber.tumblr.com, "that defeats the whole >> point of HTTPS". >> >> On Tue, Feb 14, 2017 at 1:02 PM, Ben Schwartz <bemasc@google.com> wrote: >> >>> Hi dnsop, >>> >>> I've written a draft proposal to improve the privacy of TLS connections, >>> by letting servers use the DNS to tell clients what SNI to send. >>> >>> https://tools.ietf.org/html/draft-schwartz-dns-sni-01 >>> >>> I've incorporated some helpful feedback [1] from the TLS WG, but now I >>> could use your help analyzing the DNS side. All comments welcome; this >>> draft will change based on your feedback. >>> >>> One particular issue that I could use advice on: should this be a new >>> record type, or should it reuse/repurpose an existing type like SRV or PTR? >>> >>> Thanks, >>> Ben >>> >>> [1] https://www.ietf.org/mail-archive/web/tls/current/msg22353.html >>> >> >> >> _______________________________________________ >> DNSOP mailing list >> DNSOP@ietf.org >> https://www.ietf.org/mailman/listinfo/dnsop >> >> >
- [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI Robert Edmonds
- Re: [DNSOP] Proposal for a new record type: SNI Paul Wouters
- Re: [DNSOP] Proposal for a new record type: SNI Wessels, Duane
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI Robert Edmonds
- Re: [DNSOP] Proposal for a new record type: SNI John Levine
- Re: [DNSOP] Proposal for a new record type: SNI John Levine
- Re: [DNSOP] Proposal for a new record type: SNI Warren Kumari
- Re: [DNSOP] Proposal for a new record type: SNI Adrien de Croy
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI John Levine
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI John Levine
- Re: [DNSOP] Proposal for a new record type: SNI Erik Nygren
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI John R Levine
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI John R Levine
- Re: [DNSOP] Proposal for a new record type: SNI Tony Finch
- Re: [DNSOP] Proposal for a new record type: SNI Phillip Hallam-Baker
- Re: [DNSOP] Proposal for a new record type: SNI Ben Schwartz
- Re: [DNSOP] Proposal for a new record type: SNI John Levine
- Re: [DNSOP] Proposal for a new record type: SNI Warren Kumari
- Re: [DNSOP] Proposal for a new record type: SNI John R Levine
- Re: [DNSOP] Proposal for a new record type: SNI Robert Edmonds
- Re: [DNSOP] Proposal for a new record type: SNI Phillip Hallam-Baker
- Re: [DNSOP] Proposal for a new record type: SNI John R Levine
- Re: [DNSOP] Proposal for a new record type: SNI Mark Andrews
- Re: [DNSOP] Proposal for a new record type: SNI Phillip Hallam-Baker
- Re: [DNSOP] Proposal for a new record type: SNI Mark Andrews