As Quantum Computing Evolves From Theoretical Promise To Emerging Reality, The Urgency To Develop Quantum-resilient Data Protection Mechanisms Becomes Increasingly Paramount-particularly Within Critical Infrastructure Systems Dependent On Multi-cloud Architectures. This Study Explores The Design And Deployment Of Quantum-resilient Encryption Protocols Tailored To Secure Sensitive Data Flows Across Heterogeneous And Decentralized Cloud Environments Supporting Energy, Transportation, Defense, And Healthcare Infrastructures. Beginning From A Broader Analysis Of Cryptographic Vulnerabilities Posed By Quantum Adversaries-especially Those Exploiting Shor's And Grover's Algorithms-the Paper Highlights The Limitations Of Current Asymmetric Key Systems And Symmetric Encryption Practices In Multi-cloud Data Orchestration. Building On This Foundation, The Research Narrows In On Post-quantum Cryptographic (PQC) Frameworks, Including Lattice-based, Code-based, And Multivariate Polynomial Schemes, Evaluating Their Performance And Adaptability For Dynamic Cloud-native Systems. A Key Focus Is Placed On Designing Lightweight, Interoperable Encryption Protocols That Can Seamlessly Integrate With Federated Identity Management, Zero-trust Security Models, And Real-time Data Streams Without Introducing Prohibitive Latency Or Computational Burden. The Study Also Presents An Architectural Model That Allows For Real-time Key Negotiation, Distributed Trust Management, And Algorithm Agility, Ensuring Compliance With Both Current And Forward-looking Regulatory Standards (e.g., NIST PQC Guidelines). Simulation And Benchmarking Conducted Across Hybrid Cloud Environments Demonstrate That Carefully Optimized Quantum-resilient Protocols Can Be Implemented Without Compromising System Availability Or Scalability. The Results Validate The Feasibility Of Transitioning From Conventional Cryptography To Quantum-safe Models In Mission-critical Multi-cloud Operations. The Paper Concludes By Offering A Strategic Roadmap For Organizations Seeking To Future-proof Their Cloud Infrastructures Against Quantum-era Threats.
