On the Traceability of the Accountable Anonymous Channel

Anonymous channels guaranteeing anonymity of senders such as Tor are effective for whistle-blowing and other privacy sensitive scenarios. However, there is a risk of being abused for illegal activities. As a countermeasure to illegal activities using an anonymous channel, it is natural to construct an accountable anonymous channel which can revoke anonymity of senders when an unlawful message was sent out from them. In this paper, we point out that an accountable anonymous channel THEMIS does not provide anonymity in a perfect way and there is a possibility that attackers can identify senders even if messages are not malicious. Feasibility of tracing senders is analyzed by using simulation. Moreover, we give a simple remedy of the flaw in THEMIS.