Hi everyone, I’ve been trying to understand how MiTM setups like a transparent proxy work.
Obviously, the use-case here is in a personal scope: I’d like to inspect the traffic of some of my machines. I am aware that Squid can be a transparent proxy, and some might use the Burp Suite to analyse network traffic.
Could someone explain the basic networking and the concept of certificates in this scenario? I feel like I don’t understand how certificates are used well enough.
For example: I realise that if someone inserts a root certificate in the certificate store of an OS, the machine trusts said CA, thus allowing encrypted traffic from the machine to be decrypted. However, say the machine was trying to access Amazon; won’t Amazon have its own certificate? I don’t know how I’m confused about such a simple matter. Would really appreciate your help!
I see, thanks for the explanation. Amazon sends the certificate to the proxy, and the proxy sends its own certificate, masquerading as amazon, to the user.
Thanks
Yes, I think that ‘masquerading’ is the key bit to grasp. The MITM Proxy isn’t just intercepting the traffic, it alters the traffic as it passes through.
Thanks, got it!
I think it’s important to understand how a typical SSL certificate is generated. Basically, there are a handful of companies that we have all agreeded to trust. When you download Chrome it comes with a set of trusted root certificates, so does your OS, etc. So when Amazon wants to create an SSL for amazon.com, the only way they can do that is by contacting one of those handful of trusted companies and getting them to issue a certificate that’s says Amazon.com. When you go to the site, you see a trusted party generated the cert and your browser is happy.
When you create a new root certificate and install it on your computer, you become one of those companies. So now, you can intercept traffic, decrypt it, read it, reissue a certificate for amazon.com (the same way Amazon would have gotten one from the third parties), reencrypt it, and pass it along to the client. Because the client trusts you it’s still a valid certificate. But if you inspect the certificate on the client side the root signer will no longer be GoDaddy or whatever, it will be you.
Basically, if I were to run a CA locally (on my network) and use that certificate in some OS, I should be able to set up a MiTM setup easily. Except that applications like web browsers don’t care and will utilise certificate pinning anyway, regardless of which certificates I keep in my certificate store in the OS.
Also, let’s say I’m running HAProxy/Caddy/NGINX at home which acts as my SSL-termination point for my network. In this case, if a service wants to access the internet, do these reverse proxies encrypt the outbound traffic with a different certificate?