The virtue of data forgetting has become a substantial demand in the digital era. Once online content has served its purpose, the concept of forgetting arises to ensure that data remains private between data owners and service providers. Despite significant advancements in supporting data forgetting through approaches like access heuristics, elastic expiration times, and manual revocation, the existing research falls short in addressing the demand for a multi-level forgetting structure that can cater to diverse audience-based expiration requirements while considering additional criteria. To the best of our knowledge, no prior works have investigated this gap, emphasizing the need for a comprehensive solution that can effectively accommodate the varying expiration needs of different audience groups. In this paper, we introduce a novel disjunctive multi-level forgetting scheme designed to meet the aforementioned demand for data forgetting. Our scheme introduces unique expiration periods for the encrypted data the service provider stores, called levels. Users are grouped into different levels based on priorities assigned by the data owners. Each level corresponds to a specific expiration threshold, enabling designated user groups to access the content within its validity period before it is forgotten. This approach enables selective data forgetting for one group while enabling concurrent access and retention for other user groups until the stipulated expiration period elapses. To achieve this, we have devised a cutting-edge system that integrates a hierarchical and dynamic scheme utilizing a key decay for managing expiration periods. Moreover, we introduce an innovative approach that harnesses smart contracts on a local Ethereum blockchain to enforce regulations and streamline the secure and efficient expiration and deletion of data. Finally, we thoroughly evaluate our proposed scheme, focusing on decay sensitivity, computational complexity, and rigorous security analysis.@en

During the recent development of information technology and the prevalent breakthroughs of its services, more digital data tend to be readily stored online. Although the massive advantages, there is a pivotal necessity for curating digital data forgetting. Online content can pose perilous threats in terms of privacy and security that may hinder the right to be forgotten, encompassed by the GDPR act, since the released data can be archived and accessed retrospectively. Prior approaches focused on various access heuristics and elastic expiration times to make the data unreachable to some extent. However, there are still many pending issues related to the proposed studies, such as securing ephemeral key storage and co-ownership data deletion. In this paper, we attempt to tackle the problem of storing ephemeral keys during the estimated validity period. Hence, we devise a novel concept called key decay over time, which can achieve the ephemeral existence of the key. The decay idea entails the gradual, irreversible corruption of the key with time passing. In the current work, we combine the concept of gradual time elapsing and corruption into a single notion of the decay rate. Meanwhile, the irreversibility merit formed by randomness and various obfuscation strategies impedes retrospective attacks. Over time, the decay rate will give an estimated range for the key to be destroyed entirely. Finally, we implement and thoroughly assess a proof-of-concept regarding the key decay, including computational complexity and security analysis.

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