The first time mitmproxy or mitmdump is run, a set of certificate files for the mitmproxy Certificate Authority are created in the config directory (~/.mitmproxy by default). This CA is used for on-the-fly generation of dummy certificates for SSL interception. Since your browser won't trust the mitmproxy CA out of the box (and rightly so), you will see an SSL cert warning every time you visit a new SSL domain through mitmproxy. When you're testing a single site through a browser, just accepting the bogus SSL cert manually is not too much trouble, but there are a many circumstances where you will want to configure your testing system or browser to trust the mitmproxy CA as a signing root authority.

CA and cert files

The files created by mitmproxy in the .mitmproxy directory are as follows:

mitmproxy-ca.pem The private key and certificate in PEM format.
mitmproxy-ca-cert.pem The certificate in PEM format. Use this to distribute to most non-Windows platforms.
mitmproxy-ca-cert.p12 The certificate in PKCS12 format. For use on Windows.
mitmproxy-ca-cert.cer Same file as .pem, but with an extension expected by some Android devices.

Using a custom certificate

You can use your own certificate by passing the --cert option to mitmproxy. mitmproxy then uses the provided certificate for interception of the specified domains instead of generating a cert signed by its own CA.

The certificate file is expected to be in the PEM format. You can include intermediary certificates right below your leaf certificate, so that you PEM file roughly looks like this:

-----BEGIN PRIVATE KEY-----
<private key>
-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
<cert>
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
<intermediary cert (optional)>
-----END CERTIFICATE-----

For example, you can generate a certificate in this format using these instructions:

> openssl genrsa -out cert.key 8192
> openssl req -new -x509 -key cert.key -out cert.crt
    (Specify the mitm domain as Common Name, e.g. *.google.com)
> cat cert.key cert.crt > cert.pem
> mitmproxy --cert=cert.pem

Using a custom certificate authority

By default, mitmproxy will (generate and) use ~/.mitmproxy/mitmproxy-ca.pem as the default certificate authority to generate certificates for all domains for which no custom certificate is provided (see above). You can use your own certificate authority by passing the --confdir option to mitmproxy. mitmproxy will then look for mitmproxy-ca.pem in the specified directory. If no such file exists, it will be generated automatically.

Installing the mitmproxy CA