A Systematic Survey on TPE Schemes for the Cloud: Classification, Challenges, and Future Scopes

It is now essential to ensure security because of the enormous volumes of data being exchanged. Particularly, images are very vulnerable to encryption flaws. Therefore, it is imperative to provide robust security mechanisms for image data. Conventional image encryption methods secure the privacy of necessary information by converting it into noise-like, encrypted ciphertext images that completely obscure visual content. However, the main drawback of this method is that it almost eliminates visual usability in the cloud. Thumbnail-preserving encryption (TPE) was created to solve this problem by retaining the image's thumbnail appearance even after encryption, providing a compromise between privacy and usability. Aspiring researchers should use this review to understand TPE schemes thoroughly. In this survey, the objectives, benefits, and drawbacks of several methods are examined with an emphasis on image privacy and usability. Notable TPE applications and evaluation metrics are also highlighted in the review. These metrics are grouped into categories such as quality, encryption key, security, and resilience to different kinds of attacks. In addition, a characterization of TPE schemes is provided, along with a comparison and summary of each scheme's contributions. In addition, we list the open research questions and difficulties that must be resolved to guarantee secure TPE for real-time applications.