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!
If you are acting as the proxy for the user, then all web requests go through you. A normal proxy would just forward those on to the Amazon (e.g.) server.
In your scenario, the proxy sends a cert to the client saying ‘I’m Amazon’, and the client believes it. The client talks to you like you’re Amazon, and you read all his messages. At the same time, you talk to Amazon pretending to be the user, so you can get all the correct Amazon responses to send back to the user.
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.
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.
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If you are acting as the proxy for the user, then all web requests go through you. A normal proxy would just forward those on to the Amazon (e.g.) server.
In your scenario, the proxy sends a cert to the client saying ‘I’m Amazon’, and the client believes it. The client talks to you like you’re Amazon, and you read all his messages. At the same time, you talk to Amazon pretending to be the user, so you can get all the correct Amazon responses to send back to the user.
Thanks, could you explain this a bit more? I didn’t understand what you mean by “sends a cert saying ‘I’m Amazon’”
That’s literally it. It sends a cert for amazon.com, that your client trusts, because the CA cert used to sign it is in your trusted store.
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!