## 2 Traditional Encryption Techniques
### Limitations  
Symmetric encryption algorithms, such as AES, are particularly appealing for data-intensive applications like UAV video surveillance due to their high processing speed. However, the dynamic and unpredictable characteristics of LEO communication channels exacerbate the vulnerabilities inherent in these traditional methods. For instance, phenomena such as signal attenuation and Doppler effects may disrupt the synchronization of AES keys, potentially resulting in decryption failures. Furthermore, the reliance of symmetric algorithms like AES on secure key exchange becomes problematic in LEO environments, where the dynamic nature of the communication channel increases the risk of data interception [2; 8].  
In contrast, asymmetric algorithms such as RSA offer enhanced security by employing a key pair (public and private), thereby obviating the need for secure key exchange. Nevertheless, the computational complexity associated with these algorithms imposes a considerable burden on the limited resources of UAVs, potentially causing delays in data processing and diminishing the overall system performance [3; 9]. Both AES and RSA encounter significant challenges when required to perform high-frequency key exchanges for secure, real-time UAV operations. Specifically, the pre-shared keys required by AES are difficult to synchronize amidst intermittent LEO communications, and the computational overhead of RSA hampers timely key generation and exchange in such dynamic settings.  
Moreover, scaling these traditional encryption methods to accommodate multi-UAV networks introduces additional complications, including the maintenance of synchronization across multiple dynamic nodes and the assurance of real-time data transmission [10; 11; 12; 13; 14; 15]. The asymmetric encryption in RSA creates bottlenecks when coordinating secure communication between UAVs and ground stations in agricultural monitoring applications. The AES-128 algorithm has an encryption rate of 100-200 Mbps and a computational load of 20-40 CPU cycles per byte, while the RSA-2048 algorithm has an encryption rate of 1-5 Mbps and a computational load of 5000-10,000 CPU cycles per byte [6; 7]. We consider the encryption rate and computational load, as these characteristics are critical for ensuring the encryption performance on resource-constrained UAVs and under dynamic LEO environments. This illustrates the trade-off between speed and security inherent in traditional encryption methods. For instance, AES is prized for its high speed, a critical factor for transmitting large volumes of data such as UAV video streams. Under continuous video surveillance workloads, AES demonstrates an energy efficiency advantage by consuming 20% less power than RSA, although it remains susceptible to quantum attacks [16; 17; 18; 19; 20]. In contrast, while QKD necessitates a higher initial power investment for hardware setup, it subsequently operates with significantly lower energy requirements over extended communication sessions. Conversely, the substantial computational overhead of RSA renders it more suitable for scenarios in which maximum security is paramount, even if this comes at the expense of transmission speed.  
The selection of an appropriate encryption algorithm ultimately depends on the specific requirements of the application and the desired balance between speed and security. Hybrid encryption schemes--employing AES for bulk encryption in conjunction with RSA for key exchange--have been explored to address UAV constraints. Nevertheless, these hybrid approaches encounter scalability challenges in LEO environments, as the dependence on RSA for frequent key updates introduces latency, which effectively negates the efficiency benefits achieved through AES-based data encryption.