As semiconductor supply chains become increasingly complex and globally distributed, the risks of intellectual property (IP) piracy, reverse engineering, and hardware tampering continue to intensify. Logic locking is a widely-adopted countermeasure, but traditional schemes such as XOR/XNOR-based locking and SARLock provide limited and often brittle resilience against modern attack vectors, and their effectiveness deteriorates as circuit complexity grows. We propose STREAMLOCK, a lightweight stream-cipher-driven logic locking mechanism that integrates a 128-bit Non-Linear Feedback Shift Register (NLFSR)-based keystream generator into classical circuits. By leveraging low hardware overhead, nonlinear diffusion, and dynamic keystream behavior, stream ciphers enhance resistance against unauthorized key recovery. Experimental evaluation on ISCAS'85 benchmarks shows that the proposed scheme maintains 100% functional correctness with the correct key, while a single-bit key error causes approximately 50% output corruption, demonstrating strong diffusion. Despite this increased security, STREAMLOCK incurs moderate area and power overhead, while maintaining interface resource usage comparable to or lower than conventional techniques. These results highlight that lightweight stream ciphers offer a practical and scalable approach for hardware IP protection, achieving strong security with efficient resource utilization.