  Quantum key distribution (QKD) is a revolutionary communication technology
that promises ultimate security assurance by exploiting the fundamental
principles of quantum mechanics. In this work, we report design and development
of a fully automated inter-building QKD framework for generation and
distribution of cryptographic keys, securely and seamlessly, by executing weak
coherent pulse based BB84 protocol. This framework is experimentally validated
by establishing a quantum communication link between two buildings separated by
~300m of free-space atmospheric channel. A novel synchronization technique
enabled with indigenous NavIC (IRNSS) constellation is developed and
implemented. This QKD system demonstrates generation of secure key rate as high
as 300 Kbps with QBER< 3% for mean photon no. per pulse (${\mu}$) of 0.15. The
intercept-resend eavesdropping attack has been emulated within the system and
evaluated during experiment. A novel quantum secured end-to-end encrypted video
calling app (QuViC) is also developed and integrated with QKD framework to
demonstrate unconditionally secure two-way communication over Ethernet,
functioning alongside with quantum communication.
