Proxy Re-Encryption Schemes with Proxy Having Its Own Public/Private Keys

Proxy re-encryption (PRE) allows a ciphertext computed under Alice's public key to be transformed to those which can be decrypted by Bob. Since Blaze et al. introduced the concept of proxy re-encryption in Eurocrypt'98, there are many results on proxy re-encryption. However, all the proxy re-encryption schemes proposed until now assume the proxy having no its own public/private keys. In this paper, we investigate the benefits of proxy having its own public/private keys. We find that if we allow the proxy having its own public/private key, then the proxy can not act as malicious as the proxy in the traditional PRE. The proxy can be trusted to sign on the re-encrypted ciphertext, which somewhat make the authentication on the re-encrypted ciphertext no necessary again. Based on this observation, we give two proposals to try to solve two open problems in the PRE field.