Re: WD: Inaccessibility of CAPTCHA (Call for Wide Review)

Thanks Nick, I'm particularly interested to read and see whether *Turing
Tokens* are cross compatible with the deployed *Privacy Pass* system which
seems to have a similar goal.

On Fri, Jun 28, 2019 at 1:24 PM Nick Doty <>

> As of this week, the Accessible Platform Architectures group has published
> a new draft of the Inaccessiblity of CAPTCHA document for further wide
> review. Their blog post notes changes made in this version, including a
> couple of sections on “Turing Tokens”, which is the new name they suggest
> for the blinded verification tokens that we discussed on this list during
> our review in February/March.
> Here’s the new Working Draft:
> My first take is that the new sections do consider these potential
> architectural alternatives/additions to CAPTCHAs, but that the explanations
> are not very clear — I find the paragraphs hard to read and some of the
> examples included seem confused or extraneous. They are recommending the
> creation of more federated verification token models, which may be a
> response to our on-list discussion about privacy-preserving mechanisms for
> validation of humanness without persistent identifiers. There is an
> expanded section on the “multi-device environment”, but I’m not sure it’s
> an accurate or up-to-date description of multi-factor authentication.
> None of the Github issues we opened previously have been closed and few
> have responses, although my impression is that the changes in the document
> are intended to respond to most or all of the issues we opened. The issues
> list is available here, although we don’t have the privacy issues labeled
> as privacy (which I would like):
> —Nick
> > On Feb 15, 2019, at 12:10 PM, Nick Doty <>
> wrote:
> >
> > Would any experts be willing to provide advice on this draft regarding
> CAPTCHA accessibility? There is a particular request for feedback on
> privacy and security and I think help is needed if this is going to be
> widely used analysis.
> >
> >> The APA Working Group particularly seeks feedback on the following
> questions:
> >> […]
> >>  * Are issues of privacy and security appropriately addressed?
> >
> > It’s good that privacy and security are at least being mentioned already
> in the draft, but from my quick read the general advice doesn’t seem
> especially promising.
> >
> > Biometrics are prominently listed as an easy-to-use and hard-to-defeat
> authenticator. While the caveat is in place that a biometric identifier is
> inconsistent with anonymous use of the Web, I think this also misstates the
> security properties of biometrics — since you leave fingerprints everywhere
> you go and it’s much harder to change fingers than it is passwords. And
> access to biometric identifiers is typically not available over the Web and
> there would be serious privacy concerns about adding such access, given the
> permanent and global scope of such identifiers.
> >
> > Privacy is also mentioned in this draft in Google’s reCAPTCHA, which is
> using Google account information as well as browser fingerprinting
> techniques for the “I am not a robot” checkbox. The concern is noted that
> relying on everyone to be logged in to Google while browsing the Web could
> have implications for user privacy, and that users with disabilities often
> have privacy concerns themselves. The privacy concerns could be noted more
> specifically in these sections: relying on large, centralized parties for
> embedded CAPTCHAs specifically gives the provider information about which
> site (and often, action on that site) is being used. Additinoally, the
> burdens are increased on users who aren’t logged in to the large identity
> providers, or who use techniques to inhibit browser fingerprinting.
> >
> > That federated identity, single-sign on and PKI certificates are listed
> as alternatives seems to directly conflate proving humanness with revealing
> a specific identity or identifier.
> >
> > Not mentioned are any proposed techniques for blinding tokens so that
> completing a CAPTCHA can be separated from use of the site.
> > I don’t know the current progress on “Privacy Pass” or where that’s
> going, but that seems like an especially relevant alternative to relying on
> centralized third-parties.
> >
> > If anyone involved with Tor Browser development could give advice, I
> think that would be especially helpful for this group.
> >
> > —Nick

Received on Tuesday, 2 July 2019 21:19:44 UTC