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

Rob Sayre <sayrer@gmail.com> Wed, 17 February 2021 01:01 UTC

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From: Rob Sayre <sayrer@gmail.com>
Date: Tue, 16 Feb 2021 17:01:37 -0800
Message-ID: <CAChr6SxjCXfqtZ2m8wKHk8Jmf8SyHXnfXqoT0bjp48JxYHVmbg@mail.gmail.com>
To: Carrick Bartle <cbartle891=40icloud.com@dmarc.ietf.org>
Cc: Eric Rescorla <ekr@rtfm.com>, "<tls@ietf.org>" <tls@ietf.org>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/Dp8T3Zb3hhAtL_hsN3HW7WY-LFA>
Subject: Re: [TLS] [ECH] Reverting the config ID change
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The shorter ID was described as such: "significantly limits future
flexibility."

What "flexibility" is lost?

thanks,
Rob


On Tue, Feb 16, 2021 at 4:57 PM Carrick Bartle <cbartle891=
40icloud.com@dmarc.ietf.org> wrote:

> I see. It seems reasonable to me to leave it as a variable-length vector
> to provide flexibility. Since the best mitigation for the privacy issue,
> regardless of the length of the config_id, is to have a large anonymity set
> as described in Security and Privacy Goals, it doesn't seem like a longer
> config_id is, in all cases, a major privacy trade-off.
>
>
>
> On Feb 16, 2021, at 4:34 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>
>
>
> On Tue, Feb 16, 2021 at 4:21 PM Carrick Bartle <cbartle891@icloud.com>
> wrote:
>
>>  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"?
>>
>
> It's not long enough to encode much. As a concrete example, what if the
> label is actually an encrypted version of the private key? Or you have a
> distributed generation algorithm that you don't want to synchronize?
>
> -Ekr
>
>
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