Universal re-encryption of signatures and controlling anonymous information flow

Abstract

Anonymous communication protocols, very essential for preserving privacy of the parties communicating, may lead to severe problems. A malicious server may use anonymous communication protocols for injecting unwelcome messages into the system so that their source can be hardly traced. So anonymity and privacy protection on one side and protection against such phenomena as spam are so far contradictory goals. We propose a mechanism that may be used to limit the mentioned side eects of privacy protection. During the protocol proposed each encrypted message admitted into the system is signed by a respective authority. Then, on its route through the network the encrypted message and the signature are reencrypted universally. The purpose of universal re-encryption is to hide the routes of the messages from an observer monitoring the trac. Despite re-encryption, the signature of the authority remains valid. Depending on a particular application, verification of the signature is possible either o-line by anybody with the access to the ciphertext and the signature or requires contacting the authority that has issued the signature. Our work is an extension of recent works by Golle, Jakobsson, Juels and Syverson.