[IEEE 2019 6th IEEE International Conference on Cyber Security and Cloud Computing (CSCloud)/ 2019 5th IEEE International Conference on Edge Computing and Scalable Cloud (EdgeCom) - Paris, France (2019.6.21-2019.6.23)] 2019 6th IEEE International Conference on Cyber Security and Cloud Computing (CSCloud)/ 2019 5th IEEE International Conference on Edge Computing and Scalable Cloud (EdgeCom) - Reinforcing Protection Against Chosen-Plaintext Attack Using Ciphertext Fragmentation in Multi-cloud Environments