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Re: [TLS] Captive portals, "access administratively disabled" and alert messages

Eric Rescorla <ekr@rtfm.com> Tue, 02 January 2018 21:57 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 02 Jan 2018 13:56:19 -0800
Message-ID: <CABcZeBMAqyta17umDrwMeNevPj31z6Dsi6XedaftLko8D0r-Tw@mail.gmail.com>
To: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: "<tls@ietf.org>" <tls@ietf.org>, Ted Lemon <mellon@fugue.com>
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Subject: Re: [TLS] Captive portals, "access administratively disabled" and alert messages
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On Tue, Jan 2, 2018 at 1:40 PM, Mateusz Jończyk <mat.jonczyk@o2.pl> wrote:

> CCing Ted Lemon <mellon at fugue.com> as the author of previous
> proposition.
>
> W dniu 02.01.2018 o 21:20, Eric Rescorla pisze:
> > On Tue, Jan 2, 2018 at 12:08 PM, Mateusz Jończyk <mat.jonczyk@o2.pl
> > <mailto:mat.jonczyk@o2.pl>> wrote:
> >
> >     Then the browser should display a message inside the warning screen
> that the
> >     string cannot be trusted.
> >
> > Users tend to ignore that kind of warning.
> Not any more then they ignore certificate warnings [2].


That's not clear. We would be providing some sort of attacker-controlled
text to the user with a warning that says "you can't trust this". That's
difficult to pull off.

Moreover, the certificate warnings are under control of the browser, but we
actively work to discourage the user from ignoring them. Moreover, for HSTS
sites, the browser doesn't allow the user to override them, so providing
some attacker-controlled information would make the situation materially
worse. And given that a lot of the sites which people are likely to hit
with captive portals are in fact HSTS sites (because HSTS is common in big
sites) instead showing attacker controlled information would make things
materially worse.

-Ekr

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