Re: [TLS] TLS client puzzles

Bill Cox <> Thu, 07 July 2016 17:08 UTC

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From: Bill Cox <>
Date: Thu, 07 Jul 2016 10:08:02 -0700
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To: Kyle Rose <>
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Cc: "<>" <>, Dmitry Khovratovich <>
Subject: Re: [TLS] TLS client puzzles
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On Wed, Jul 6, 2016 at 1:16 PM, Kyle Rose <> wrote:

> On Wed, Jul 6, 2016 at 4:08 PM, Hannes Tschofenig <
>> wrote:
>> I agree with Brian here on this issue. This is clearly impractical for
>> IoT devices. For many of those devices we are talking about 32 KB (in
>> total).
> I continue to feel like this is a valid objection to the wrong
> proposition. I don't think the question is, "Should TLS client puzzles be
> issued by all TLS servers under load?" but rather, "Would client puzzles be
> a useful addition to the DDoS toolbox, and appropriate in some cases?"
> Kyle

I agree, and I think it is clear that client puzzles can be a useful
addition to the DDoS defense toolbox.  However, most of this can be handled
at the higher levels above TLS, or possibly as a custom extension that does
not complicate TLS.

The most similar effort I know of is one I work on: token binding.  Rather
than bake it into TLS, we're using the custom extension API.  If there were
a separate effort to standardize client puzzles, similar to what we are
doing with token binding, I would be interested in participating.