Witness encryption with updatable ciphertexts

Witness encryption with updatable ciphertexts

연구 분야: Analysis

학회: Science China Information Sciences

Witness encryption (WE) is a novel type of cryptographic primitive that enables a message to be encrypted via an NP instance. Anyone who possesses a solution to this instance (i.e., a witness) can then recover the message from the ciphertext. We introduce a variant of WE that allows ciphertext updates, referred to as ciphertext updateable WE (CUWE). With CUWE, a user can encrypt a message using an instance x and a tag t, and those who possess a valid witness w for x and match the access policy defined by tag t can decrypt the message. Furthermore, CUWE allows for the use of an update token to change the tag t of ciphertext to a different tag. This feature enables fine-grained access control, even after the ciphertext has been created, thereby significantly increasing the usefulness of the WE scheme. We demonstrate that such a WE framework with an updatable ciphertext scheme can be constructed using our puncturable instance-based deterministic encryption (PIDE) and indistinguishability obfuscation . We also propose an instantiation of PIDE utilizing puncturable pseudorandom functions (PRFs) that provide (selectively) indistinguishable security. Finally, we expand our CUWE to ciphertext-updatable functional WE (CUFWE), which offers enhanced data access control.