Ensuring Efficient and Secure Updatable Encryption in Cloud Storage

With the widespread adoption of cloud computing, individuals and companies are increasingly storing data in encrypted form on cloud servers. However, the continuous evolution of attack methods poses a persistent threat to the security of user keys. This paper proposes a model in which, with the involvement of the server, users periodically rotate keys, and the server acts as a proxy to facilitate ciphertext updates. This approach eliminates the need to download data to the local environment for updates before re-uploading, thereby saving bandwidth. We present a specific encryption scheme that ensures even in the transmission through an insecure channel, tokens used for ciphertext updates do not disclose key information from the previous or subsequent epochs—a concept previously unrealizable in practice. Our solution relies on the widely used and simple DDH (Decisional Diffie-Hellman) assumption, and the length of our ciphertext does not increase with the progression of epochs.