But the connection between the user and the VPN server could still be sniffed. Let's say I live in Boulder, CO, and there's an IXP in Denver. Due to the hierarchical nature of the internet topology, my ISP's upstream link goes through that IXP. Every connection from every subscriber of my ISP goes through that IXP. So it doesn't matter if I'm using a bridge that the NSA doesn't recognize as a Tor entry point, or the obfs3 protocol which they can't DPI, or a VPN server in Argentina. If they control SR's HSDir and the IXP, then when I fetch the SR descriptor, they can include a traffic signature that is detected by the IXP, which sees the IP address that the packets are headed to, which is me. It doesn't matter how many layers of encryption I add, or how many VPNs or proxy hops I add, as long as the IXP is between me and the first hop. Theoretically the NSA could inject a traffic signature that is detectable by the IXP through all those hops and layers of encryption. Yes, I think this could help. When the Chaos Computer Club published their results of Tor circuit fingerprinting, I read that it could be trivially defeated by loading pages in another tab.