[cryptography] Allergy for client certificates

Tony Arcieri bascule at gmail.com
Tue Oct 8 18:41:18 EDT 2013


On Mon, Sep 30, 2013 at 9:55 AM, Guido Witmond <guido at witmond.nl> wrote:

> On 09/30/13 17:43, Adam Back wrote:
> > Anyway and all that because we are seemingly alergic to using client side
> > keys which kill the password problem dead.
>
>
> Hi Adam,
>
> I wondered about that 'allergy' myself. I have some ideas about that and
> I'm curious to learn about other.


We use client certs extensively for S2S authentication where I work
(Square).

As for web browsers, client certs have a ton of problems:

1) UX is *TERRIBLE*. Even if you you tell your browser to use a client cert
for a given service, and you go back to that service again, browsers often
don't remember and prompt you EVERY TIME to pick which cert to use from a
giant list. If you have already authenticated against a service with a
given client cert, and that service's public key hasn't changed, there's
absolutely no reason to prompt the user every single time to pick the cert
from all of the client certs they have installed.

2) HTML <keygen> tag workflow is crap and confusing. It involves
instructing users to install the generated cert in their browser, which is
weird and unfamiliar to begin with. Then what? There's no way to
automatically direct users elsewhere, you have to leave a big list of
instructions saying "Please install the cert, then after the cert is
installed (how will the user know?) click this link to continue"

3) Key management UX is crap: where are my keys? That varies from browser
to browser. Some implement their own certificate stores. Others use the
system certificate store. How do I get to my keys? For client certs to
replace passwords, browsers need common UI elements that make managing,
exporting, and importing keys an easy process.

Passwords may be terrible, but they're familiar and people can actually use
them to successfully log in. This is not the case for client certs. They're
presently way too confusing for the average user to understand.

-- 
Tony Arcieri
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