TUM Logo

The Pairing Problem: A Systematic Review

The Pairing Problem: A Systematic Review

Supervisor(s): Ludwig Peuckert
Status: open
Topic: Others
Type of Thesis: Masterthesis Bachelorthesis


Chair of IT Security / Prof. Dr. Claudia Eckert

The Pairing Problem: A Systematic Review

Consider a set of devices in principle capable of engaging in communication with each other (e.g. the set of Bluetooth capable devices).
Now consider that we pick two nodes A and B from such set.
We want applications running on each of these nodes to be able to communicate with each other without any third party being able to tamper or eavesdrop their communication, and being completely aware and certain about this ability.
This is for instance desired when we purchase a Bluetooth capable smartphone and headset and want to connect them to lead hands-free confidential conference-calls.
An alternative example is when we want to establish a connection between our smartphone wallet and the POS terminal of a store when purchase something.

The question is now, how can the applications on A and B achieve to establish such a communication channel?
This situation is called the 'Pairing Problem' more precisely characterized as the task of establishing a long-term connection between two previously unknown devices. Unknown involves i.e. the following two restrictions.
First, pairing partners do not share any key material they could use in a key exchange or to authenticate each other (this would require an individual preinstalled key for each device combination inside the ecosystem).
Second, solutions involving a central trusted third party (e.g., PKI) are not applicable (this would require a connection for all devices to such global authority).

To solve the Pairing Problem devices need to identify and leverage a shared trust anchor.
Common trust anchors are a low bandwidth OOB channel with certain security properties or physical limitations such as spatial distance.
The availability of a certain trust anchor for a specific device depends on the abilities of this device.
These abilities, however, vary greatly and so a large variety of methods coined for specific use cases exist.
While [1], [2], [3], and [4] proposed reviews for the field,  they focus on a elemen perspective and examine trust anchors and methods one by one.
No work examining the Pairing Problem from a bigger perspective and accounting for the interconnection of methods exists.   

This is especially problematic for the security of general purpose scenarios as in Bluetooth, where the goal is to connect any to devices supporting its radio interface.
As a solution different methods are eligible (e.g. Numeric Comparison, Passkey Entry, and Just Works in Bluetooth).
While these combinations introduce security implications and issues as shown in [5], they are not widely discussed in the research community.

This leads to a number of research questions for the proposed thesis:

- Which trust anchors exist?

- How to systematize the field? Which sub problems or related problems exist? Identify consistent definitions and formulate new definitions where needed!

- Which methods exist? Which trust anchors do they leverage? In which scenarios are they applicable, are they realistic? 

- How are different methods combined in general purpose systems and which security implications follow?

- Many methods leverage DH using trust anchors, could we leverage other KE methods?

- Which role plays UI and the user? Which role plays a third party? 


  • Knowledge in Protocol Security
  • Ideally obtained from the lectures IT-Security and Secure Mobile Systems or IT-Security 2