# About Certificates
Mitmproxy can decrypt encrypted traffic on the fly, as long as the client trusts mitmproxy’s built-in certificate authority. Usually this means that the mitmproxy CA certificate has to be installed on the client device.
# Quick Setup
By far the easiest way to install the mitmproxy CA certificate is to use the built-in certificate installation app. To do this, 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, follow the setup instructions for the platform you’re on and you are good to go.
# The mitmproxy certificate authority
The first time mitmproxy is run, it creates the keys for a certificate
authority (CA) in the config directory (
~/.mitmproxy by default).
This CA is used for on-the-fly generation of dummy certificates for each visited website.
Since your browser won’t trust the mitmproxy CA out of the box, you will either need to click through a TLS certificate
warning on every domain, or install the CA certificate once so that it is trusted.
The following files are created:
|mitmproxy-ca.pem||The certificate and the private key in PEM format.|
|mitmproxy-ca-cert.pem||The certificate in PEM format. Use this to distribute on 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.|
For security reasons, the mitmproxy CA is generated uniquely on the first start and is not shared between mitmproxy installations on different devices. This makes sure that other mitmproxy users cannot intercept your traffic.
# Installing the mitmproxy CA certificate manually
Sometimes using the quick install app is not an option and you need to install the CA manually.
Below is a list of pointers to manual certificate installation
documentation for some common platforms. The mitmproxy CA cert is located in
~/.mitmproxy after it has been generated at the first start of mitmproxy.
- curl on the command line:
curl --proxy 127.0.0.1:8080 --cacert ~/.mitmproxy/mitmproxy-ca-cert.pem https://example.com/
- wget on the command line:
wget -e https_proxy=127.0.0.1:8080 --ca-certificate ~/.mitmproxy/mitmproxy-ca-cert.pem https://example.com/
- macOS (automated):
sudo security add-trusted-cert -d -p ssl -p basic -k /Library/Keychains/System.keychain ~/.mitmproxy/mitmproxy-ca-cert.pem
- Mozilla Firefox
- Chrome on Linux
On recent iOS versions you also need to enable full trust for the mitmproxy root certificate:
- Go to Settings > General > About > Certificate Trust Settings.
- Under “Enable full trust for root certificates”, turn on trust for the mitmproxy certificate.
- iOS Simulator
sudo keytool -importcert -alias mitmproxy -storepass changeit -keystore $JAVA_HOME/lib/security/cacerts -trustcacerts -file ~/.mitmproxy/mitmproxy-ca-cert.pem
- Android/Android Simulator
- Windows (automated):
certutil -addstore root mitmproxy-ca-cert.cer
# Upstream Certificate Sniffing
When mitmproxy receives a request to establish TLS (in the form of a ClientHello message), it puts the client on hold and first makes a connection to the upstream server to “sniff” the contents of its TLS certificate. The information gained – Common Name, Organization, Subject Alternative Names – is then used to generate a new interception certificate on-the-fly, signed by the mitmproxy CA. Mitmproxy then returns to the client and continues the handshake with the newly-forged certificate.
Upstream cert sniffing is on by default, and can optionally be disabled by turning the
upstream_cert option off.
# Certificate Pinning
Some applications employ Certificate Pinning to prevent man-in-the-middle attacks. This means that mitmproxy’s certificates will not be accepted by these applications without modifying them. If the contents of these connections are not important, it is recommended to use the ignore_hosts feature to prevent mitmproxy from intercepting traffic to these specific domains. If you want to intercept the pinned connections, you need to patch the application manually. For Android and (jailbroken) iOS devices, various tools exist to accomplish this:
- apk-mitm is a CLI application that automatically removes certificate pinning from Android APK files.
- objection is a runtime mobile exploration toolkit powered by Frida, which supports certificate pinning bypasses on iOS and Android.
- ssl-kill-switch2 is a blackbox tool to disable certificate pinning within iOS and macOS applications.
Please propose other useful tools using the “Edit on GitHub” button on the top right of this page.
# Using a custom server certificate
You can use your own (leaf) certificate by passing the
--certs [domain=]path_to_certificate option to mitmproxy. Mitmproxy then uses the
provided certificate for interception of the specified domain 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 your 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 # (Specify the mitm domain as Common Name, e.g. \*.google.com) openssl req -new -x509 -key cert.key -out cert.crt cat cert.key cert.crt > cert.pem
Now, you can run mitmproxy with the generated certificate:
For all domain names
mitmproxy --certs *=cert.pem
For specific domain names
mitmproxy --certs *.example.com=cert.pem
*.example.com is for all the subdomains. You can also use
www.example.com for a particular subdomain.
# 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
--set confdir=DIRECTORY option to
mitmproxy. Mitmproxy will then look for
mitmproxy-ca.pem in the
specified directory. If no such file exists, it will be generated
mitmproxy-ca.pem certificate file has to look roughly like this:
-----BEGIN PRIVATE KEY----- <private key> -----END PRIVATE KEY----- -----BEGIN CERTIFICATE----- <cert> -----END CERTIFICATE-----
When looking at the certificate with
openssl x509 -noout -text -in ~/.mitmproxy/mitmproxy-ca.pem
it should have at least the following X509v3 extensions so mitmproxy can
use it to generate certificates:
X509v3 extensions: X509v3 Key Usage: critical Certificate Sign X509v3 Basic Constraints: critical CA:TRUE
# Using a client side certificate
You can use a client certificate by passing the
option to mitmproxy. Using a directory allows certs to be selected based on
hostname, while using a filename allows a single specific certificate to be used
for all TLS connections. Certificate files must be in the PEM format and should
contain both the unencrypted private key and the certificate.
# Multiple client certificates
You can specify a directory to
--set client_certs=DIRECTORY, in which case the matching
certificate is looked up by filename. So, 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.