[cryptography] Allergy for client certificates

Guido Witmond guido at witmond.nl
Fri Oct 11 05:07:14 EDT 2013


On 10/10/13 20:12, Michael Rogers wrote:
> On 10/10/13 09:29, Guido Witmond wrote:
>>> It looks like you've worked around the UX issues by inserting an 
>>> EC-aware proxy between the client and server. Who would be
>>> responsible for deploying such proxies?
> 
>> That proxy lives in the end user's computers. Right now, the user
>> needs to install the proxy. I hope to get time and funding to make
>> it a Firefox plug in. I hope that when it proofs useful browsers
>> will adopt it.
> 
> I hope you manage to persuade browsers to support it, because it seems
> like it will be difficult to get sites to adopt EA until their users
> can reliably expect it to be supported on every machine they use.

Browser support would be a big breakthrough.


> (Sorry for referring to EA as EC in my last email!)

It's not a trademark or so. As long as it's clear from the context I'm
fine with it. :-)


> My family and friends outside the tech community are quite casual
> about logging into their accounts from friends' machines, work
> machines, internet cafes, etc. It's all very well for us to say that's
> a bad idea, but we can't deny it's convenient to be able to log in
> from anywhere with nothing but a password.

If the computers and browsers were designed to protect the users against
many risks, it would not be a problem. However, most browsers are
designed by companies that don't deliver that promise. We are slowly
getting there with things like sandboxing, partitioning. See
qubes-os.org and Genode.org.

There is also the cryptostick, a usb/smartcard combo. The first
generation can hold only 3 keys. When we have one that can hold a few
hundred, it makes it easier. People can carry them along. As each
certificate/key only fits one site, the amount of damage is limited to
the sites that any malware can reach. And there are ways to obfuscate
the name of the site where that key fits. A hash of the sitename, with a
simple password as index to the keys.


> I can definitely see the benefits of EA for users who have a few
> personal devices that are synced and not shared with other users, and
> who value the security of using their own devices more than the
> convenience of being able to log in from anywhere. That describes me,
> but it doesn't describe most of the people I know.

It's a thing that we, system architects/crypto-plumbers need to address.
To give a (always flawed) analogy: People expect a Volvo in terms of
security when they read the brochure but all they get is a T-Ford. It
requires a lot of care to keep it safe and going.

I don't blame the people for having these expectations. We need to make
it happen.

> Perhaps you could think of a killer app for EA that appeals to people
> whose habits match the way EA works?

One feature is the ease of signing up at web sites. Just click. No more
hassles with email address, links to click, waiting for that message to
come through the spam filter, grey-lists. Immediate login.

That could be a good feature for web shops. No more hassle with making
accounts. A single click for customers to create an account, and you
have a secure channel for a credit card transaction.

As shop, offer a public RSS-feed with promotions instead of an email
list. Make an encrypted RSS-feed and you have a personalised channel.
Now make it tempting for customers to sign up and you get to see what
each customer is interested in.

If you send to much, your customers can unsubscribe by deleting the feed
in their browser, knowing that you cannot reach them anymore. When they
come back, you know it to if they use the same account. Otherwise, learn
to be less agressive. Treat your customers as kings, and they appreciate it.


Another (not a killer)-feature (for users) is that they are in control
of the account. When they delete the private key, their account is
closed. No one else can come later and claim the account. Unless they
copied the private key beforehand.


A benefit for site operators is that there is no personal data lying
around in case of a breach of the server. Some european politicians
already propose heavy fines (500.000 euros) for leaking personal
details. Even if your customer was so stupid to re-use their gmail
password for your little shop, you get the blame for leaking it.

A smaller benefit, all traffic between you and your customer is
encrypted so there can be no spying by people that want to plaster their
advertisement onto your shop. What Phorm in the UK tried to do.


This is all possible just by having a local CA that signs client
certificates and a user agent that uses that.


I hope you this list offers anything to kill for?


Regards, Guido.



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