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Adding Caido's CA Certificate to the System Partition: Virtual Device ​

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For convenience, consider adding all installed tools/tool packages to your system PATH environment variable to avoid navigation/the need to use absolute paths in commands.

In this tutorial, we will cover the process of adding Caido's CA certificate to the system-store of a virtual Android device.

Renaming Caido's CA Certificate ​

In order for Caido's CA certificate to be compatible with the Android system, it will need to meet the expected naming format. The format is the legacy hash of a CA certificate's subject field with a .0 extension.

System storage certificate names.

To generate the correct certificate file name:

  1. Navigate to http://127.0.0.1:8080/ca.crt in a browser on your computer to download Caido's CA certificate.

  2. Open a terminal and navigate to the file system location of the certificate and enter the following command:

openssl x509 -inform PEM -subject_hash_old -in ca.crt
  1. Rename the certificate to the returned hash (located between the command and -----BEGIN CERTIFICATE-----) with a .0 extension.

Adding the Certificate ​

NOTE

This method will only work for virtual devices with an Android API level <= 33.

To add the certificate to the system level certificate storage of the device:

  1. In the Projects interface of the Android Studio window, click on the More Actions button and select SDK Manager.
SDK Manager.

  1. Select Android SDK from the Languages & Frameworks drop-down menu.

  2. Open a terminal and navigate the the file system location stated in the Android SDK Location field.

Android SDK Location.

  1. Navigate into the emulator directory.

  2. Execute the emulator tool with -list-avds to ensure the device is listed.

bash
./emulator -list-avds
  1. Execute the emulator tool with the name of your device as the value of the -avd argument and writeable-system (if your device is currently running, terminate it first by clicking the button of its associated row in the Device Manager window).
bash
./emulator -avd <device-name> -writable-system

  1. Open a new terminal and and navigate the the file system location stated in the Android SDK Location field.

  2. Navigate into the platform-tools directory.

  3. Execute the adb tool with devices to ensure the device is listed.

bash
./adb devices
List of connected virtual Android devices.
  1. Execute the adb tool with the device ID as the value of the -s argument and root to gain root privileges.
bash
./adb -s <device-id> root
Restarting for root privileges.
  1. Execute the adb tool against the device with shell avbctl disable-verification to disable secure boot verification.
bash
./adb -s <device-id> shell avbctl disable-verification
Disabling verification.
  1. Execute the adb tool against the device with reboot to reboot the device.
bash
./adb -s <device-id> reboot
  1. Once the device has rebooted, gain root privileges again.
bash
./adb -s <device-id> root
  1. Execute the adb tool against the device with remount to modify the partition permissions as read/write.
bash
./adb -s <device-id> remount
Remounting.
  1. Execute the adb tool against the device with the file system location of the renamed certificate as the value of the push argument to move it into the System partition.
bash
./adb push </path/to/certificate/hash.0> /system/etc/security/cacerts
Remounting.
  1. Execute the adb tool with shell chmod 664 -v to set the proper permissions on the certificate by specifying its file system location on the device.
bash
./adb -s <device-id> shell chmod 664 -v /system/etc/security/cacerts/<hash.0>
Certificate permissions.
  1. Reboot the device again for the changes to take effect.
bash
./adb -s <device-id> reboot
  1. Execute the adb tool against the device with reverse tcp:8080 tcp:8080 to forward traffic to Caido.
bash
./adb -s <device-id> reverse tcp:8080 tcp:8080

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To verify the addition of the certificate:

  1. On the device, navigate to the Settings interface.

  2. In the Search settings input field, search for and select Trusted credentials.

  3. Click on Trusted credentials and locate Caido in the System tab certificate list.

Once the certificate has been installed, interacting with certain applications on the device will add rows to the HTTP History traffic table in Caido.

NOTE

If traffic is not appearing in the HTTP History table in Caido, try:

  • Disabling Mobile data usage.

  • Disabling any VPN connections.

  • Setting the Wi-Fi Proxy hostname to 10.0.2.2.

If application traffic is still not proxied through Caido or you are encountering errors/limitations in functionality, continue with the Modifying an Android Application tutorial.