  Cooperative perception is crucial for connected automated vehicles in
intelligent transportation systems (ITSs); however, ensuring the authenticity
of perception data remains a challenge as the vehicles cannot verify events
that they do not witness independently. Various studies have been conducted on
establishing the authenticity of data, such as trust-based statistical methods
and plausibility-based methods. However, these methods are limited as they
require prior knowledge such as previous sender behaviors or predefined rules
to evaluate the authenticity. To overcome this limitation, this study proposes
a novel approach called zero-knowledge Proof of Traffic (zk-PoT), which
involves generating cryptographic proofs to the traffic observations. Multiple
independent proofs regarding the same vehicle can be deterministically
cross-verified by any receivers without relying on ground truth, probabilistic,
or plausibility evaluations. Additionally, no private information is
compromised during the entire procedure. A full on-board unit software stack
that reflects the behavior of zk-PoT is implemented within a specifically
designed simulator called Flowsim. A comprehensive experimental analysis is
then conducted using synthesized city-scale simulations, which demonstrates
that zk-PoT's cross-verification ratio ranges between 80 % to 96 %, and 80 % of
the verification is achieved in 2 s, with a protocol overhead of approximately
25 %. Furthermore, the analyses of various attacks indicate that most of the
attacks could be prevented, and some, such as collusion attacks, can be
mitigated. The proposed approach can be incorporated into existing works,
including the European Telecommunications Standards Institute (ETSI) and the
International Organization for Standardization (ISO) ITS standards, without
disrupting the backward compatibility.
