mitmproxy 0.13 - About Certificates

# About Certificates

## On This Page

- Introduction
- Quick Setup
- Installing the mitmproxy CA certificate manually
- More on mitmproxy certificates
- CA and cert files
- Using a custom certificate
- Using a client side certificate
- Using a custom certificate authority

## Introduction

Mitmproxy can decrypt encrypted traffic on the fly, as long as the client trusts its built-in certificate authority. Usually this means that the mitmproxy CA certificates have to be installed on the client device.

## Quick Setup

By far the easiest way to install the mitmproxy certificates is to use the built-in certificate installation app. To do this, just start mitmproxy and configure your target device with the correct proxy settings. Now start a browser on the device, and visit the magic domain mitm.it. You should see something like this:

Click on the relevant icon, and follow the setup instructions for the platform you're on, and you are good to go.

## Installing the mitmproxy CA certificate manually

Sometimes using the quick install app is not an option - Java or the IOS similator spring to mind - or you just need to do it manually for some other reason. Below is a list of pointers to manual certificate installation documentation for some common platforms:

iOS Simulator | Java
iOS | Android/Android Simulator
Windows | Mac OS X
Ubuntu/Debian | Firefox
Chrome on Linux

## More on mitmproxy certificates

The first time mitmproxy or mitmdump is run, the mitmproxy Certificate Authority(CA) is created in the config directory (~/.mitmproxy by default). This CA is used for on-the-fly generation of dummy certificates for each of the SSL sites that your client visits. Since your browser won't trust the mitmproxy CA out of the box , you will see an SSL certificate warning every time you visit a new SSL domain through mitmproxy. When you are 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 certificate 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 2048
    $ 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 client side certificate

You can use a client certificate by passing the `--client-certs DIRECTORY` option to mitmproxy. If you visit example.org, mitmproxy looks for a file named example.org.pem in the specified directory and uses this as the client cert. The certificate file needs to be in the PEM format and should contain both the unencrypted private key and the certificate.

## Using a custom certificate authority

By default, mitmproxy will use `~/.mitmproxy/mitmproxy-ca.pem` as the 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.