I am Matthias Fassl from the CISPA Helmholtz Center for Information Security and I am going
to present our paper on exploring a user-centered security design approach for authentication
ceremonies.
Let's begin by clarifying what we mean by authentication ceremonies so end-to-end encrypted
communication is susceptible to so-called man-in-the-middle attackers and these attackers
eavesdrop on conversation partners by making them use the wrong keys.
And most mobile messengers such as WhatsApp, Signal, Telegram provide so-called authentication
ceremonies so that users can detect these kinds of attacks.
This slide actually shows Signal's authentication ceremony on iOS.
There people have to meet up and scan each other's QR code to verify the security of
the communication channel.
However, these authentication ceremonies have several issues.
So, first of all most users are not aware of them, and those who know that they exist
have problems using them correctly or do not really understand their exact purpose.
And also there is always the issue of social friction such as embarrassment for not exactly
knowing what's going on.
So despite valuable prior research, these problems are still ongoing.
So we decided to try something different and design authentication ceremonies from the
ground up. So instead of starting with a security mechanism
we started with the users' perceptions on authentication and then tried match a security
mechanism to these perceptions. So our design process included collaborative
design workshops to get an idea of how users imagine how authentication should work.
Then a security expert selected viable conceptual designs.
And then we used iterative storyboard prototyping together with users and a UX expert to develop
these prototypes further. In the end we used a mixed-methods online
evaluation to compare our prototypes with Signal's authentication ceremony.
So this process resulted in three prototypes. First of all, a selfies-based prototype where
each user takes selfies of themselves that shows a verification action.
Then a ID-card based prototype where people meet up to verify each other's security card.
And lastly, and most successful in our evaluation: a prototype based on a combination lock, where
users choose a combination they want to use to lock the conversation, when they lock the
channel they get a notification that it's locked and that they need to share the PIN
with their conversation partner. And then they use a secure channel or they
meet up so that the other conversation partner enters this access code.
And then the conversation can continue.
When we asked the participants what kind of attacks they thought these ceremonies protected
against we found that participants who saw the selfies-based prototype where less confident
in its security then participants who were in the control group.
Participants who saw the combination-lock based prototype where more confident in its
security.
We can partially explain this with qualitative data:
So while participants in the selfies-based prototype condition were convinced in the
authenticity of their conversation partner, the prototype did not really explain how process
would secure the communication channel itself. On the other hand, the combination lock prototype's
security was on the surface easy to understand for participants, even though they might understand
zero-knowledge proof in the background.
The most important lessons we learned were: it is important to have clear expectations
from participants. They are not security or UX experts, but nevertheless
we can gain valuable insights from their conceptual ideas.
and also that misunderstandings early on in the design process can influence the prototypes
throughout the process.
For future design projects we would be more specific about our choice of participants
and also increase our focus on iterative qualitative evaluation.