## 3 Proposed Approach: Quantum Key Distribution (QKD)
### Detailed Description of the Data Encryption and Compression Algorithm  
The AES-128 algorithm, chosen for its efficiency and suitability for resource-constrained devices like UAVs, operates with a block size and key length of 128 bits, employing a substitution-permutation network structure across 10 rounds. The LZW algorithm provides lossless data compression, typically achieving a 30-50% reduction in data volume, which enhances the transmission efficiency and indirectly improves security by minimizing the transmission time. The QKD (BB84) protocol, selected for its relative ease of implementation and proven efficiency, utilizes the polarization of single photons in two mutually unbiased bases, with an expected key generation rate of 10-100 Mbps. In the proposed methodology, a hybrid security framework that integrates Quantum Key Distribution (QKD) for secure key management with AES-128 symmetric encryption for data protection is employed. QKD facilitates the secure generation and distribution of cryptographic keys, while AES-128 is responsible for the encryption and decryption of data. AES-128 is utilized to encrypt data due to its high encryption throughput and relatively low computational overhead, rendering it ideal for deployment on UAVs with constrained resources. This algorithm processes data in 128-bit blocks using a 128-bit key and is structured around multiple rounds of substitutions and permutations. Such a design ensures a high degree of confusion and diffusion, thereby enhancing resistance against a range of cryptanalytic attacks. The hybrid system is designed to optimize resource utilization by offloading the computationally intensive QKD processes to ground stations whenever feasible, while UAV onboard systems prioritize the rapid execution of AES-128. This approach minimizes the energy burden associated with QKD and ensures uninterrupted, real-time encryption even under constrained operational conditions. For secure key exchange, the system employs the QKD (BB84) protocol, which is fundamentally based on the principles of quantum mechanics. This protocol provides information-theoretic security for key transfer, rendering it robust against even quantum computer-based attacks. The hybrid architecture leverages the speed and reliability of AES-128 in conjunction with the rigorous security guarantees provided by QKD. In the unlikely event of QKD link degradation, pre-established AES keys are employed to maintain secure data transmission without compromising confidentiality or integrity. Specifically, the BB84 protocol transmits key information using photons polarized in two mutually unbiased bases. Any attempt at interception perturbs the photon states, thereby signaling the presence of an intruder. Additionally, to enhance the performance of the BB84 protocol under low-bandwidth and high-latency conditions, dynamic error correction thresholds and adaptive reconciliation processes have been integrated. Field simulations indicate that these enhancements can yield up to a 20% improvement in key generation rates, ensuring seamless integration within the hybrid system. To mitigate the challenges posed by a limited communication bandwidth--especially in low Earth orbit scenarios--the Lempel-Ziv-Welch (LZW) lossless data compression algorithm is implemented [17]. The LZW algorithm builds a dictionary of frequently occurring character sequences, enabling efficient, lossless data compression. Depending on the nature and structure of the data, the algorithm typically achieves a compression ratio resulting in a 30-50% reduction in data volume. Although LZW may introduce a slight risk of error propagation during decompression, particularly in noisy transmission environments, this risk is addressed by integrating error detection mechanisms at the compression level. These measures ensure that any corrupted packets are identified and flagged for retransmission prior to decompression, thereby significantly enhancing the data rates in bandwidth-constrained environments.