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An Improved Construction for Reusable Anonymous Return Channels Based on Universal Re-encryption

Reusable anonymous return channels proposed by Golle and Jakobsson allow any recipient of one of the anonymous messages in a mix net to send back one or more replies directly. Yet their protocol has an obvious efficiency problem caused by multiple rounds of message processing. In this paper, we introduce a technique which is based on universal re-encryption and increases the total efficiency of reusable anonymous return channels. Our protocol retains all the significant attributes of the reusable channels, known as compos ability, reusability, transferability and compatibility. And it reduces the processing rounds of a message so as to increase efficiency. Moreover, it produces some new important properties. When using our protocol, even if all the servers in our system are corrupted, they can not gain the information of message content and our system can not be easily used as a decryption oracle. We also improve the efficiency of our original protocol when processing long messages and present a hybrid construction for it. Using Pohlig-Hellman, a message is much shorter in our hybrid construction than it is in our primary construction. As a result, the larger a message is, the more efficient our hybrid construction becomes.