  We theoretically propose and experimentally demonstrate the use of a
configurable four-qubit photonic system to generate a publicly verifiable
quantum random numbers, to perform entanglement verification, and to generate a
secure public and private key. Quantum circuits, to generate the desired
four-qubit states and its experimental realization in the photonic architecture
is carried out using photon pairs entangled in polarization and path degree of
freedom. By performing measurements on the four-qubit system and accessing
partial information of the four-qubit state for public verification, we
generate publicly verified and purely secured random bits at the rate of 370
kbps. When the system is used for generating public and private keys, an equal
number of public and private keys are generated simultaneously. We also record
about 97.9\% of sampled bits from four-qubit states passing entanglement
verification. The theoretical model of noise on the four-qubit state and its
effect on the generation rate of verified and secured bits are in perfect
agreement with the experimental results. This demonstrates the practical use of
the small-scale multi-qubit photonic system for quantum-safe applications by
providing the option for real-time verification of the security feature of the
quantum system.
