Recipient Anonymity: An Improved Crowds Protocol Based on Key Sharing

Crowds, which is a classical P2P anonymous communication protocol, adopts random forwarding to effectively provide a privacy preserving way of accessing the web with good expansibility, without web sites being able to recognize who is browsing. However, it does not provide anonymity against global eavesdroppers. Furthermore, recipient anonymity and relationship anonymity are not implemented by Crowds. This paper utilizes the characteristic that IPv6 protocol allows user-defined IPv6 options to improve Crowds anonymous communication protocol. The contributions of our improved Crowds protocol (Crowds6) are as follows: 1. It makes other relays of the re-routing path correctly get last-hop's address by adding a self-defined option in sender's packet to store last-hop's address; 2. When sender sends packets, it uses last-hop's public key to encrypt symmetry key which is used to decode the message content, so only the last-hop can get recipient's address, resolving the key sharing problem between sender and last-hop, and achieving recipient anonymity to some extent. The theoretical analysis and simulation results show that our improved Crowds protocol effectively resolves the problem that other relays of the re-routing path can not correctly get last-hop's address, and performances better than traditional anonymous protocol on defending predecessor attack by utilizing the key sharing technology, at the same time, recipient anonymity is also realized while the communication delay is reduced.