Importing a Certificate and Installing it on Android

In this quick tutorial, we’ll cover the process of importing a certificate into an Android device using a series of command-line commands. This can be particularly useful for various security-related tasks or when working with self-signed certificates.

Prerequisites

Before we begin, make sure you have the following:

• A certificate file in DER format (cacert.der)
• An Android device connected to your computer via USB
• A working knowledge of the command line

Step 1: Convert DER to PEM

The first step is to convert the DER-encoded certificate to PEM format. Run the following command:

openssl x509 -inform DER -in cacert.der -out cacert.pem

This command takes the DER-encoded certificate (cacert.der) and converts it to PEM format (cacert.pem).

Step 2: Generate the Certificate Hash

Next, you’ll generate the subject hash for the certificate. Run the following command:

openssl x509 -inform PEM -subject_hash_old -in cacert.pem | head -1

This command extracts the subject hash from the PEM certificate.

Step 3: Copy the Certificate to Android

Now, copy the PEM certificate to your Android device’s SD card:

cp cacert.pem 9a5ba575.0
adb push 9a5ba575.0 /sdcard

This sequence of commands copies the cacert.pem file to 9a5ba575.0 and pushes it to the SD card of your Android device using ADB (Android Debug Bridge).

Step 4: Mount the System Partition

To install the certificate, you’ll need to mount the system partition as read-write. Depending on your Android version and device, you can try one of the following commands:

adb shell
mount -o rw,remount /system

or

adb shell
mount -o rw,remount /

Use the appropriate mount command based on your device's configuration.

Step 5: Copy the Certificate to the System

Once the system partition is mounted as read-write, copy the certificate to the system’s security certificates folder:

cp /sdcard/9a5ba575.0 /system/etc/security/cacerts/

This command copies the certificate to the /system/etc/security/cacerts/ directory.

Step 6: Set Appropriate Permissions

Finally, set the appropriate permissions for the certificate:

cd /system/etc/security/cacerts/
chmod 644 9a5ba575.0

This command changes the permissions of the certificate file to allow read access.

And that’s it! You’ve successfully imported a certificate into your Android device’s system. This can be particularly useful when dealing with secure connections or custom certificates in various Android applications.

Remember to exercise caution when modifying system files on your Android device, as it can potentially lead to instability if done incorrectly. Always ensure you have a backup and know what you’re doing before making system changes.