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Re: [TLS] About encrypting SNI

David Holmes <d.holmes@f5.com> Mon, 12 May 2014 18:02 UTC

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From: David Holmes <d.holmes@f5.com>
To: Eric Rescorla <ekr@rtfm.com>, Brian Sniffen <bsniffen@akamai.com>
Thread-Topic: [TLS] About encrypting SNI
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Date: Mon, 12 May 2014 18:01:53 +0000
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Cc: "tls@ietf.org" <tls@ietf.org>, Andy Lutomirski <luto@amacapital.net>
Subject: Re: [TLS] About encrypting SNI
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➢ so a server under load can, in the initial opportunistic encryption phase, push back to a client and ask for a puzzle to be solved?

I was describing this idea to a colleague, and the first thing he said was "could you have the client mine some bitcoin for you? As a show of good faith?"

Two problems sprung to mind with a bitcoin mining solution - unethical servers would be gaming clients to do computation for them. Second, this would also a cause a problem for mobile handsets where CPU = battery life.

But I think the puzzle idea has merit, especially if it's not a required challenge = that is, only issued when server is under load.


From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Eric Rescorla
Sent: Thursday, April 17, 2014 2:20 PM
To: Brian Sniffen
Cc: tls@ietf.org; Andy Lutomirski
Subject: Re: [TLS] About encrypting SNI

On Thu, Apr 17, 2014 at 12:59 PM, Brian Sniffen <bsniffen@akamai.com> wrote:
I hesitate to ask, but: is it plausible to re-open the proof-of-work
conversation, so a server under load can, in the initial opportunistic
encryption phase, push back to a client and ask for a puzzle to be
solved?

I don't think it's implausible (though I'm not completely sold yet).

One concern I would have is whether we understand the problem well
enough to actually specify this. I'm not an expert in this area, but weren't
there a bunch of concerns about designing puzzles that were effective
without being prohibitively expensive for mobile devices? How would
we design a new kind of puzzle (As opposed to messing with the puzzle
work factor) and then roll it out?

-Ekr

> I wonder if there's a way to test a large number of private keys at
> once.  If so, then the cost drops to O(log N).  Off the top of my
> head, I can't think of a cryptosystem with that property.
I certainly don't expect to find any *pair* of cryptosystems with that
property, and continue to maintain that in 3 years we won't find two big
organizations willing to use exactly the same crypto.

-Brian

--
Brian Sniffen
Information Security
Akamai Technologies
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