Abstract. We introduce a new cryptographic technique that we call universal re-encryption. A conventional cryptosystem that permits re-encryption, such as ElGamal, does so only for a player with knowledge of the public key corresponding to a given ciphertext. In contrast, universal re-encryption may be performed without knowledge of public keys. We demonstrate an asymmetric cryptosystem with universal re-encryption that is half as e cient as standard ElGamal in terms of both computation and storage. While technically and conceptually simple, universal re-encryption leads to new types of functionality in mixnet architectures. Conventional mixnets are often called upon to enable players to communicate with one another through channels that are externally anonymous, i.e., that hide information permitting tra c-analysis. Universal re-encryption permits a mixnet of this kind to be constructed in which servers hold no public or private keying material, and may therefore dispense with the cumbersome requirements of key generation, key distribution, and private-key management. We describe two highly practical mixnet constructions, one involving asymmetric input ciphertexts, and another for hybrid-ciphertext inputs.
Proxy re-encryption should not be confused with the universal re-encryption REF , in which the ciphertexts are re-randomized instead of changing the underlying public key.
Universal Re-encryption for Mixnets
CT-RSA
Computer Science