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Re: [TLS] [ECH] Reverting the config ID change

Carrick Bartle <cbartle891@icloud.com> Wed, 17 February 2021 00:21 UTC

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From: Carrick Bartle <cbartle891@icloud.com>
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Date: Tue, 16 Feb 2021 16:21:46 -0800
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Cc: Martin Thomson <mt@lowentropy.net>, "<tls@ietf.org>" <tls@ietf.org>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] [ECH] Reverting the config ID change
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>  It's not significant extra complexity to have this field bigger and it basically makes it impossible to have any structure.

What do you mean by structure? How does a byte not provide sufficient "structure"?



> On Feb 16, 2021, at 3:33 PM, Eric Rescorla <ekr@rtfm.com> wrote:
> 
> 
> 
> On Tue, Feb 16, 2021 at 3:01 PM Martin Thomson <mt@lowentropy.net <mailto:mt@lowentropy.net>> wrote:
> On Wed, Feb 17, 2021, at 08:31, Christopher Wood wrote:
> > That's true, but I'd personally prefer one tracking vector to two. This 
> > structure also better aligns with other proposed use cases for HPKE 
> > configurations. I also don't see an immediate need for flexibility in 
> > this value given that there are extensions in ECHConfigContents already.
> 
> I don't see the tracking angle as relevant here.  The only things that might matter is size, collision probability (for greasing), and consistency.  Size doesn't matter, because it's a handful of bytes at most; collisions matter little because the cost is a resource the server is prepared to spend anyway; consistency with something that can also change isn't worth much.
> 
> The primary argument I would have in support of this is YAGNI.  The number of active keys should be much smaller than 256, and there's a slot for extensions should that need arise.
> 
> I don't find YAGNI that persuasive in this case. It's not significant extra complexity to have this field bigger and it basically makes it impossible to have any structure.
> 
> -Ekr
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