How to use application's client certificate with Charles?

Question

Trying to investigate private APIs on apps installed on my Android, I've noticed most modern apps use custom client certificate meaning with the trusted root certificate installed on the Android, Charles still cannot monitor the traffic because the server would reject the handshake from Charles. I imagine either I will need a different tool for the traffic monitoring or I will need to direct Charles to use some custom certificate file embedded in the app itself.

Ziegler

Answer 1

You need that certificate file at hand (I don't know if and how you can extract it from application).

You also need to know the passphrase (password) for that certificate. Charles will ask it when you connect to selected host for 1st time.

Then just use latest Charles (tested on version 4.2.1) menu Proxy -> SSL Proxying Settings, tab Client Certificates and add certificate (PKCS#12 key file) for selected host and port.

Gratt

Even if you could extract the client certificate, would it be possible to decrypt all communications? – Yore