How does Fiddler work with HTTPS

Question

I made HTTP proxy server. But the problem that I can't decrypt SSL traffic.

I found that Fiddler install Trust Root Certificate. I did the same and now I don't have error that certificate untrusted but I got other error: wrong Common Name (CN). How fiddler change the CN of installed trusted certificate?

Will appreciate any answer.

Answer 1

Fiddler acts as an SSL termination proxy. Ie the connection goes like this:

Browser ---(SSL handshake)---> Fiddler --- (SSL handshake) ---> Actual Site

So your connection is first time encrypted and sent to Fiddler, where it is first decrypted by Fiddler and then again encrypted to be sent to the actual site that you access.

Additionally when you access a site Fiddler automatically generates a server certificate with a CN that is equal to the host name of the site and this certificate is signed by the CA of fiddler That's why Fiddler needs to install a set of trusted CAs in your browser so that the first SSL handshake can be made against a trusted authority.