[Security] TLS Certificates Verification

Dirk Meyer dmeyer at tzi.de
Wed Aug 20 05:25:38 CDT 2008

Jonathan Dickinson wrote:
> I think the client MUST guide the user through installing the key on
> a thumbdrive. However, the wizard MUST NOT require the user to put
> the key on a thumbdrive. I usually lose my thumbdrive once every two
> weeks (_dime a dozen_), I would obviously take care of my XMPP one,
> but that means at times I don't have one lying around to just
> install a new key on. 

We have to think on different levels here. One is the security done by
machines and the other one is the user interface. There are several
ideas how to put usability on complex situations.

E.g. Shared secret: We must keep an open mind what kind of secrets we
have. There are several ideas to make it work besides passwords: md5
sum of an image from a shared vacation (the app must take care of the
md5), when you connect you set-top box it could show a 2d barcode and
you take a photo, ...

The password for the key is like a shared key. You do not have to
think about it as a password, be creative. It could be your
fingerprint. While fingerprints are easy to manipulate, the attacker
must know it is the fingerprint. So the user only has to remember that
the password is created by his left thumb. The password again could be
the md5 sum of an important photo you have multiple backups of.

In all cases the unser interface must guide the user.

> I know a couple of people who don't even know what a thumbdrive is
> (they also use gopher).

I also did not know the term thumbdrive, but I know wikipedia :)


Always remember you're unique, just like everyone else.

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