Quantum cryptography leverages principles from quantum mechanics to advance secure data transmission, posing significant improvements over classical cryptographic systems. As quantum computing evolves, traditional cryptographic methods reliant on complex mathematical operations, such as prime factorization and discrete logarithms, face increased vulnerability to quantum-based attacks. Quantum Key Distribution (QKD) has emerged as a vital quantum cryptographic method, allowing secure key exchanges resistant to eavesdropping and cyber threats. This study systematically reviews the role of numerical methods in enhancing quantum cryptographic protocols, particularly regarding efficiency, scalability, and security. These methods, including Monte Carlo techniques, density matrices, and quantum state tomography, play critical roles in simulating quantum states and error correction, which are crucial for QKD's reliability. Furthermore, the study examines number-theoretic functions fundamental to quantum security systems and investigates how large-scale numerical computations impact the scalability of these protocols. Findings suggest that while quantum cryptography offers unbreakable security potentials, challenges in real-world implementation persist, primarily due to computational demands and environmental noise. Future work focuses on optimizing quantum cryptographic protocols to overcome these challenges and fully harness the potential of quantum-secured networks.