A Story About Bypassing Air Canada's In-Flight Network Restrictions

Summary

1 Prologue#A while ago, I took a flight from Canada back to Hong Kong - about 12 hours in total with Air Canada.Interestingly, the plane actually had WiFi: However, the WiFi had restrictions. For Aeroplan members who hadn’t paid, it only offered Free Texting, meaning you could only use messaging apps like WhatsApp, Snapchat, and WeChat to send text messages, but couldn’t access other websites.If you wanted unlimited access to other websites, it would cost CAD $30.75: And if you wanted to watch videos on the plane, that would be CAD $39: I started wondering: for the Free Texting service, could I bypass the messaging app restriction and access other websites freely?Essentially, could I enjoy the benefits of the $30.75 paid service without actually paying the fee? After all, with such a long journey ahead, I needed something interesting to pass the 12 hours.Since I could use WeChat in flight, I could also call for help from the sky.Coincidentally, my roommate happens to be a security and networking expert who was on vacation at home. When I mentioned this idea, he thought it sounded fun and immediately agreed to collaborate. So we started working on it together across the Pacific.2 The Process#After selecting the only available WiFi network acwifi.com on the plane, just like other login-required WiFi networks, it popped up a webpage from acwifi.com asking me to verify my Aeroplan membership. Once verified, I could access the internet. There’s a classic software development interview question: what happens after you type a URL into the browser and press enter?For example, if you type https://acwifi.com and only focus on the network request part, the general process is: DNS query -> TCP connection -> TLS handshake -> HTTP request and response. Let’s consider github.com as our target website we want to access. Now let’s see how we can break through the network restrictions and successfully access github.com.3 Approach 1: Domain Self-Signing#Since acwifi.com is accessible ...