Re: [Add] avoiding unnecessary metadata in applications doing DNS / DoH

Moving thread from ADD to DPRIVE.

I would suggest reaching out to the authors of
https://tools.ietf.org/html/draft-dickinson-doh-dohpe-00 if you're
interested in advancing that line of work.

One major challenge related to User-Agent is forming a workable threat
model.  It seems likely that an interested server could easily identify
distinct user agents, even without this header field.  For example, the TLS
fingerprint alone is sufficient to uniquely identify most TLS
implementations[1], and different HTTP/2 implementations produce different
framing patterns.  Active probing (e.g. returning slightly invalid
responses and observing how the client reacts) would likely allow the
server to identify the client software completely.

It's harder to motivate this kind of protection if it only works against
"friendly" servers, especially because the User-Agent is extremely useful
for server operations, capacity planning, etc.

The DOHPE draft also contains several other suggestions (e.g. removing
locale and language preference information) that may be easier to justify.

[1] https://tlsfingerprint.io/

On Thu, Apr 11, 2019 at 3:12 PM nusenu <nusenu-lists@riseup.net> wrote:

>
> DNS never had something like a user-agent field and that is fine,
> but since browsers send one by default during their (non-DoH) operations
> it is likely that they and other DoH clients will send the user-agent
> along with their DoH queries.
>
> This exposes unnecessary metadata to the resolver, something that
> didn't exist on the resolver before DoH.
>
> Since RFC8484 does not require user-agent headers
> applications implementing DoH should not include
> such metadata by default.
> Some DoH implementations do it currently but it is early
> enough to improve that.
>
>
> DoH Privacy Enhancement: Do not set the user-agent header for DoH requests
> https://bugzilla.mozilla.org/show_bug.cgi?id=1543201
>
>
>
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Re: [Add] avoiding unnecessary metadata in applications doing DNS / DoH

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