Symmetric Blind Decryption with Perfect Secrecy
This work addresses privacy-preserving encrypted file storage and payment systems by enabling secure decryption queries without revealing plaintext information, representing a foundational advance in cryptography.
The paper tackled the problem of achieving information-theoretically secure blind decryption, which was previously thought impossible, by formulating a definition of perfect secrecy for symmetric blind decryption and devising a scheme based on modular arithmetic on a ring Z_p^2 that satisfies this notion.
A blind decryption scheme enables a user to query decryptions from a decryption server without revealing information about the plaintext message. Such schemes are useful, for example, for the implementation of privacy preserving encrypted file storages and payment systems. In terms of functionality, blind decryption is close to oblivious transfer. For noiseless channels, information-theoretically secure oblivious transfer is impossible. However, in this paper we show that this is not the case for blind decryption. We formulate a definition of perfect secrecy of symmetric blind decryption for the following setting: at most one of the scheme participants is a malicious observer. We also devise a symmetric blind decryption scheme based on modular arithmetic on a ring $\mathbb{Z}_{p^2}$, where $p$ is a prime, and show that it satisfies our notion of perfect secrecy.