API Keys

Using local.properties

We can use local.properties to store API keys and other sensitive information. This file is not checked into version control, so it is safe to store sensitive information here.

local.properties

API_KEY=MyAPIKeyInLocalProperties

l̥ build.gradle

// Make this section buildFeatures, and set buildConfig to true
buildFeatures {
    buildConfig = true
}

defaultConfig {
    // Get values from local.properties
    val properties = Properties()   // Properties of java.util
    properties.load(project.rootProject.file("local.properties").inputStream())
    buildConfigField("String", "API_KEY", "\"${properties.getProperty("API_KEY")}\"")
}

l̥ MainActivity.java

String API_KEY = BuildConfig.API_KEY

Using ProGuard

Another methods is to use obfuscation. This is a method of hiding the API key in the code. This is not a very secure method, but it is better than nothing.

It is done by using ProGuard. ProGuard is a tool that is used to obfuscate code. It is used to make the code smaller and faster. It is also used to make the code more secure.

In order to do this, set isMinifyEnabled to true in the build.gradle file.

build.gradle

buildTypes {
    release {
        isMinifyEnabled = true
        proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
    }
}

Using NDK

Step 1: Set Project view in the Android Studio

Step 2: go to app -> src -> main

Step 3: Right click on main, and select "Add C++ to module" from context menu

This will generate two files required

CMakeLists.txt
native-lib.cpp (other name can be used in place of 'native-lib')

And this will also add the following code in build.gradle

defaultConfig {
    externalNativeBuild {
        cmake {
            cppFlags += ""
        }
    }
}

externalNativeBuild {
    cmake {
        path = file("src/main/cpp/CMakeLists.txt")
        version = "3.22.1"
    }
}

Step 4: Add this code in MainActivity to dynamically load the C++ library into our application

static {
    System.loadLibrary("native-lib");
}

Step 5: Now write this line of code

public native String getApiKey();

At this point, getApiKey() will return null, We need to implement it in native-lib.cpp.

IDE will show an error on this line, because we have not implemented it yet.

Right click on the error and select "Create JNI function for getApiKey()"

Step 6: Now the code will look like this

#include <jni.h>
// Some Comments
extern "C"
JNIEXPORT jstring JNICALL
Java_com_ripalnakiya_apikeysndk_MainActivity_getApiKey(JNIEnv *env, jobject thiz) {
    // TODO: implement getApiKey()
}

Step 7: Now we need to return the API key from this function. So replace the comment with the following code

jstring API_KEY = (jstring) "MyAPIKeyInNDK";
return env->NewStringUTF(reinterpret_cast<const char *>(API_KEY));

Step 8: Now we can use this API key in our MainActivity.java file

String API_KEY = getApiKey();

Last modified: 05 February 2026