RHyTHM: A Randomized Hybrid Scheme To Hide in the Mobile Crowd
This addresses privacy issues for vehicles in intermittent connectivity scenarios, but it is incremental as it builds on existing pseudonym and anonymous authentication methods.
The paper tackles the problem of vehicle privacy when connectivity to pseudonym infrastructure is lost, proposing RHyTHM to allow disconnected vehicles to use on-the-fly pseudonyms without being tracked, achieving enhanced privacy with reasonable computational overhead.
Any on-demand pseudonym acquisition strategy is problematic should the connectivity to the credential management infrastructure be intermittent. If a vehicle runs out of pseudonyms with no connectivity to refill its pseudonym pool, one solution is the on-the-fly generation of pseudonyms, e.g., leveraging anonymous authentication. However, such a vehicle would stand out in the crowd: one can simply distinguish pseudonyms, thus signed messages, based on the pseudonym issuer signature, link them and track the vehicle. To address this challenge, we propose a randomized hybrid scheme, RHyTHM, to enable vehicles to remain operational when disconnected without compromising privacy: vehicles with valid pseudonyms help others to enhance their privacy by randomly joining them in using on-the-fly self-certified pseudonyms along with aligned lifetimes. This way, the privacy of disconnected users is enhanced with a reasonable computational overhead.