  The amount of information generated grows as more and more sensor and IoT
devices are deployed in smart cities. It is of utmost importance for us to
consider the privacy data leakage and compromised identity from both outside
adversaries and inside abuse of data access privilege. The security assumption
of the system should not solely rely on the fact that permission and access
control were being implemented correctly. Quite the contrary, a system can be
designed in a way that user's identity data and usage traces are not leaked
even if the system had been compromised. Based upon our previous on-street
parking system utilizing Bluetooth Low Energy (BLE) beacons, we applied a
cryptographic primitive called zero-knowledge proof to our authentication
system. A commitment scheme and Merkle tree is combined in the setup to achieve
zero-knowledge set membership proof. Doing so, the user is anonymous to the
server between authentication sessions, while the server's still able to verify
the legitimacy of such user. The on-street parking system is therefore immune
to privacy data leakage, as for now one cannot mass-query and profile certain
user's traces within the system.
