Re: [MLS] Fwd: Re: multiple devices per user?

Eric Rescorla <ekr@rtfm.com> Sun, 25 March 2018 12:23 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sun, 25 Mar 2018 05:23:08 -0700
Message-ID: <CABcZeBMA7u11+8wtX-vx72Xhyax=nbZaPRzTkZ-oRamfW=ySuQ@mail.gmail.com>
To: Simon Friedberger <simon.tls@a-oben.org>
Cc: mls@ietf.org
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Subject: Re: [MLS] Fwd: Re: multiple devices per user?
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On Sun, Mar 25, 2018 at 3:53 AM, Simon Friedberger <simon.tls@a-oben.org>
wrote:

> (Copy to the list.)
>
> Hi Eric!
>
>
> >
> >     Eric:
> >     > it's that there are use cases in
> >     > which users want to add a new device without an existing device
> >     being
> >     > online, and these are incompatible with type #0 designs.
> >
> >     I'm not sure that devices being added is such a common occurence
> >     that it
> >     would prohibit asking for authorization from a different device.
> >
> >
> > OK. I guess Jon and others who run IM services can weigh in here on
> > their experience, but
> > I can tell you about Mozilla's experience in a not-dissimilar setting,
> > namely browser sync.
> > Firefox used to have a system which required interaction between the
> > original device
> > and the one to be enrolled, and we found it to be a very aversive user
> > experience which
> > we eventually abandoned in favor of a more conventional password based
> > design.
> >
> Indeed that sounds much better. So how does this work? The user encrypts
> their data with a password derived key and you use some form of
> challenge response for authentication so you never get the password?
>

This is documented at:
https://github.com/mozilla/fxa-auth-server/wiki/onepw-protocol


So for MLS this would translate to the service provider holding password
> encrypted packets with pre-approved authentication keys from a known
> good device?
>

Well, I wasn't suggesting we adopt the Firefox protocol, merely that the UX
requirements of a scheme which required key transfer were not good.

-Ekr


>
> Best Regards,
> Simon
>
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