Signing APKs

This tutorial shows how to create a signed release APK of your project with AndroidIDE.

Introduction

This tutorial covers the following topics :

• Create a keystore file with AndroidIDE Terminal.

• Configure Gradle to use the signing key.

• Verify APK signature.

Creating the keystore

For creating the keystore file, we’ll use keytool that is provided by OpenJDK. You can execute the keytool -h command to check if the tool is available or not. If you do not see the help message, you might need to perform the basic setup before you can proceed with next steps.

Open the terminal and follow the instructions to create the keystore.

First of all, you need to cd into the directory where you want to store the keystore file. For this tutorial, we’ll be storing the keystore in the AndroidIDEProjects directory in the internal storage. Execute the following command to cd into the projects’ directory :

cd $PROJECTS

Here, PROJECTS is an environment variable whose value is the absolute path of the projects’ directory.

To create a new keystore file, execute the following command :

keytool -genkey -v -keystore signing-key.jks -keyalg RSA -keysize 2048 -validity 9125 -alias myAlias

Explanation :

• -genkey : Command used to create new keystore with keytool.

• -v : For verbose output.

• -keystore signing-key.jks : Specifies the filename of the output keystore file. In this example, the keystore file will be saved as signing-key.jks.

• -keyalg RSA : Specifies the key algorithm to use for the keystore.

• -keysize 2048 : The number of bits in the key used by the key algorithm.

• -validity 9125 : The validity of the key, in days. In this example, the value is 9125 days which is equal to 25 years.

• -alias myAlias : The key alias.

Learn more about keytool.

After you execute the above command, you’ll be asked to provide additional information about the keystore. After you enter the required information, the keystore file will be created.

Configuring Gradle

We need to add signingConfig in the app/build.gradle file. The signingConfig specifies the keystore which will be used to sign the build variants of your application. To do this, we need to copy the signing-config.jks file to the app module’s directory of our project. So go ahead and copy the file.

Then edit your app/build.gradle file like this :

android {
    ...
    signingConfigs {
        release {
            // Specify the name of your keystore file
            // The file must be located in your module directory
            storeFile file("signing-key.jks")

            // The keystore password
            storePassword "test1234"

            // The key alias, same as the one you specified with '-alias' argument while creating the keystore
            keyAlias "myAlias"

            // The key password
            keyPassword "test1234"
        }
    }

    // specify the signingConfig to use for release build type
    buildTypes {
        release {
            signingConfig signingConfigs.release
        }
    }
    ...
}

That’s it! You can now run :app:assembleRelease task to assemble the release build of your project. The resultant APK will be signed with the signing-key.jks file.

Verify APK Signature

You can use the apksigner tool provided by the Android SDK Build Tools to verify the signature of the APK. To do this, just execute the following command :

$HOME/android-sdk/build-tools/<build-tools-version>/apksigner verify --print-certs /path/to/your/app.apk

# For example
$HOME/android-sdk/build-tools/33.0.3/apksigner verify --print-certs $PROJECTS/MyApplication/app/build/outputs/apk/release/app-release.apk

This will print the information about the APK’s signature. You can learn more about the apksigner tool here.