Privacy Preserving Collaborative Enforcement of Firewall Policies in Virtual Private Networks

The widely deployed Virtual Private Network (VPN) technology allows roaming users to build an encrypted tunnel to a VPN server, which, henceforth, allows roaming users to access some resources as if that computer were residing on their home organization's network. Although VPN technology is very useful, it imposes security threats on the remote network because its firewall does not know what traffic is flowing inside the VPN tunnel. To address this issue, we propose VGuard, a framework that allows a policy owner and a request owner to collaboratively determine whether the request satisfies the policy without the policy owner knowing the request and the request owner knowing the policy. We first present an efficient protocol, called Xhash, for oblivious comparison, which allows two parties, where each party has a number, to compare whether they have the same number, without disclosing their numbers to each other. Then, we present the VGuard framework that uses Xhash as the basic building block. The basic idea of VGuard is to first convert a firewall policy to nonoverlapping numerical rules and then use Xhash to check whether a request matches a rule. Comparing with the Cross-Domain Cooperative Firewall (CDCF) framework, which represents the state-of-the-art, VGuard is not only more secure but also orders of magnitude more efficient. On real-life firewall policies, for processing packets, our experimental results show that VGuard is three to four orders of magnitude faster than CDCF.