  A key challenge in censorship-resistant web browsing is being able to direct
legitimate users to redirection proxies while preventing censors, posing as
insiders, from discovering their addresses and blocking them. We propose a new
framework for censorship-resistant web browsing called {\it CensorSpoofer} that
addresses this challenge by exploiting the asymmetric nature of web browsing
traffic and making use of IP spoofing. CensorSpoofer de-couples the upstream
and downstream channels, using a low-bandwidth indirect channel for delivering
outbound requests (URLs) and a high-bandwidth direct channel for downloading
web content. The upstream channel hides the request contents using
steganographic encoding within email or instant messages, whereas the
downstream channel uses IP address spoofing so that the real address of the
proxies is not revealed either to legitimate users or censors. We built a
proof-of-concept prototype that uses encrypted VoIP for this downstream channel
and demonstrated the feasibility of using the CensorSpoofer framework in a
realistic environment.
