Remote inspection of adversary-controlled environments

Remotely monitoring the location and enduring presence of valuable items in adversary-controlled environments presents significant challenges. In this article, we demonstrate a monitoring approach that leverages the gigahertz radio-wave scattering and absorption of a room and its contents, including a set of mirrors with random orientations placed inside, to remotely verify the absence of any disturbance over time. Our technique extends to large physical systems the application of physical unclonable functions for integrity protection. Its main applications are scenarios where parties are mutually distrustful and have privacy and security constraints. Examples range from the verification of nuclear arms-control treaties to the securing of currency, artwork, or data centers. Remotely monitoring valuable items in adversary-controlled environments constitutes an intricate problem. Traditional inspection and surveillance methods are not always possible to implement or may fall short of meeting stringent security and privacy requirements. It may be difficult and perhaps impossible to permit regular physical inspections or placing CCTV cameras in such secure environments to offer some level of confidence in the integrity of stored items. Agreed managed-access inspections leave open the possibility of inspectors gathering information. Providing confidence that relevant surveillance data are originating from the correct location and have not been pre-recorded could prove challenging when the environment is controlled by an adversarial party. In this context, specialized surveillance hardware and cryptographic tools are at risk of hacking and spoofing. An example for this problem can be found in the monitoring of non-deployed strategic and tactical nuclear warheads as part of an arms-control agreement. These warheads represent 70% of the global nuclear arms stockpile and remain outside of existing agreements because of the difficulties to monitor them. They are stored in dedicated bunkers at sensitive military or nuclear sites. The presence and number of such weapons at any given site cannot be verified easily via satellite imagery or other national technical means that are unable to see into the storage vaults. To include them in future arms control initiatives, there is a need to develop technologies and protocols to reliably assess if weapons declared as being in storage are not removed. Here we propose and demonstrate a new remote monitoring approach based on a radio-wave measurement system to generate fingerprints of a room and its content using an array of randomly oriented mirrors to verify that nothing changes over time. This approach only requires a single on-site visit to initialize the monitoring protocol to install the mirrors and take an initial imprint of the room. Our approach builds on the concepts of physical unclonable functions (PUFs) and virtual proofs of reality, for which data authenticity, confidentiality, and integrity does not rely on digital keys and algorithms but on the inherent material complexity of physical systems to achieve privacy and security objectives. Our work shows that large-scale systems such as an entire room and its content can also be turned into physical unclonable functions.

Johannes Tobisch, Sébastien Philippe, Boaz Barak, Gal Kaplun, Christian Zenger, Alexander Glaser, Christof Paar, Ulrich Rührmair