A hybrid cryptosystem for cloud security: combining Okamoto-Uchiyama and Advanced Encryption Standard for optimized encryption performance

The central challenge in cloud computing is delivering strong data protection while maintaining high system performance. This paper addresses the problem by developing a hybrid cryptosystem that integrates the strengths of Okamoto-Uchiyama (OU) and Advanced Encryption Standard (AES). For key transfer, the model employs secure OU public-key encryption to prevent key compromise in transit, and AES for fast symmetric encryption of large data bursts when required. As a result, AES handles data encryption operations while OU was used solely for key exchange, avoiding the usual overhead associated with asymmetric encryption. The hybrid system was deployed in the cloud and compared with asymmetric models such as RSA. Test results showed that the proposed system outperforms existing approaches by reducing encryption and decryption times by nearly 90% for large-scale data without compromising security. It also provides extended resistance to common attacks, including brute-force and man-in-the-middle (MITM) attacks, supporting its practical applicability in cloud environments. The hybrid cryptosystem offers an optimal balance of performance and security, making it suitable for current cloud computing applications such as SaaS, PaaS, and IaaS.