Proxy re-encryption (PRE) is a cryptosystem that realizes efficient encrypted data sharing by allowing a third party proxy to transform a ciphertext intended for a delegator (i.e., Alice) to a ciphertext intended for a delegatee (i.e., Bob). Attribute-based proxy re-encrypftion (AB-PRE) generalizes PRE to the attribute-based scenarios, enabling fine-grained access control on ciphertexts. However, the existing AB-PRE schemes do not adequately address the following problems: (1) the risk of decryption key leakage, and (2) the need of time-based delegation. To resolve these problems, we introduce a primitive called time-based attribute-based proxy re-encryption (TB-AB-PRE) with decryption key update. TB-AB-PRE associates keys with the current time information and supports efficient periodical decryption key update for each time transition. This property guarantees that a compromise of a decryption key for some time does not breach the security of ciphertexts from the others. Leveraging this time-based property, the proposed TB-AB-PRE elegantly achieves time-based delegation which enables Alice to decide which ciphertexts can be transformed and their decryptable timeframe after being transformed. The proposed construction is proven to be secure against honest re-encryption attacks with decryption key exposure resistance, under the learning with errors assumption.

代理重加密（PRE）是一种密码系统，它通过允许第三方代理将委托者（即 Alice）的密文转换为委托者（即 Bob）的密文来实现高效的加密数据共享。基于属性的代理重加密（AB-PRE）将 PRE 推广到基于属性的场景，从而实现对密文的细粒度访问控制。然而，现有的AB-PRE方案没有充分解决以下问题：（1）解密密钥泄漏的风险，以及（2）基于时间的委托的需要。为了解决这些问题，我们引入了一种称为基于时间的基于属性的代理重加密（TB-AB-PRE）的原语，具有解密密钥更新功能。 TB-AB-PRE 将密钥与当前时间信息相关联，并支持每次时间转换的高效定期解密密钥更新。此属性保证解密密钥在一段时间内的妥协不会破坏其他密文的安全性。利用这种基于时间的属性，所提出的 TB-AB-PRE 优雅地实现了基于时间的委托，使 Alice 能够决定可以转换哪些密文以及转换后的可解密时间范围。在错误学习假设下，所提出的结构被证明可以安全地抵御具有解密密钥暴露抵抗力的诚实重加密攻击。