What is an APK and why does it need to be signed?
An APK (Android Package Kit) is a file format that contains all the components of an Android app, such as code, resources, assets, and manifest. An APK is used to distribute and install Android apps on devices.
Before you can publish your app on Google Play or other app stores, you need to sign your APK with a digital certificate. Signing your APK ensures that:
you uploaded an apk that is signed with a different certificate to your previous apks
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Your app is authentic and comes from you, the original developer.
Your app has not been tampered with or modified by anyone else.
Your app can be updated securely and consistently.
Your app can access certain features and APIs that require app signing, such as Google Play App Signing, Google Play Licensing, Google Play Protect, and Google Play Instant.
What is an APK signing certificate?
An APK signing certificate is a public-key certificate that contains information about you and your app, such as your name, organization, and app's package name. The certificate also contains a public key that corresponds to a private key that only you have access to.
When you sign an APK, you use your private key to create a digital signature for the APK. The signature is attached to the APK and can be verified by anyone using your public key, which is embedded in the certificate. The verification process ensures that the APK has not been altered and that it comes from you.
An APK signing certificate is also known as a keystore, a key, or an alias. You can generate an APK signing certificate using various tools, such as Android Studio, keytool, or apksigner.
What are the benefits of signing your APK?
Signing your APK has several benefits for you and your users, such as:
Security: Signing your APK prevents unauthorized modifications or malware injections that could compromise your app or harm your users. It also protects your app from being impersonated by other developers who might try to use your app's identity or reputation.
Updates: Signing your APK enables you to update your app seamlessly and consistently. Android devices only accept app updates that are signed with the same certificate as the installed app. This prevents someone else from publishing an update for your app that could harm your users or steal their data.
Compatibility: Signing your APK enables you to use certain features and APIs that require app signing, such as Google Play App Signing, Google Play Licensing, Google Play Protect, and Google Play Instant. These features and APIs help you distribute your app more efficiently, protect your app from piracy, enhance your app's security and performance, and deliver your app to users instantly without installation.
What happens when you upload an APK that is signed with a different certificate to your previous APKs?
If you try to upload an APK that is signed with a different certificate to your previous APKs, you will encounter an error message that says something like this:
"Upload failed. You uploaded an APK that is signed with a different certificate to your previous APKs. You must use the same certificate. Your existing APKs are signed with the certificate(s) with fingerprint(s): [SHA1: 12:34:56:78:90:AB:CD:EF:12:34:56:78:90:AB:CD:EF:12:34:56:78] and the certificate(s) used to sign the APK you uploaded have fingerprint(s): [SHA1: 23:45:67:89:01:BC:DE:F0:23:45:67:89:01:BC:DE:F0:23:45:67:89]"
This error means that Android has detected a mismatch between the signing certificates of your new and old APKs. This prevents you from uploading the new APK to Google Play or other app stores. a reset of your app signing key, if you meet the following conditions: - You are enrolled in Google Play App Signing, which is a service that lets Google manage and protect your app signing key for you. - You have the original app signing key that you used to sign the first APK that you uploaded to Google Play. - You have not yet published your app to any tracks or released it to any users. If you meet these conditions, you can follow these steps to request a reset of your app signing key: - Create a new key and keystore that you want to use as your new app signing key. Make sure it is different from any previous keys that you have used. - Sign an APK with the new key and keystore, using the same package name and version code as the last APK that you uploaded to Google Play. - Fill out and submit the [contact form] for Google Play support, and attach the APK signed with the new key, the original app signing key, and the upload certificate for the original app signing key. The upload certificate is a public-key certificate that identifies your upload key, which is the key that you use to sign APKs before uploading them to Google Play. You can get your upload certificate by using the [App Signing by Google Play] page in the Play Console, or by using the [PEM export] feature of keytool or apksigner. - Wait for Google Play support to review your request and contact you with the next steps. This option will allow you to keep your existing app and users, but it may take some time and effort to complete. You should only use this option as a last resort, and only if you are sure that you have the original app signing key.
How to sign your APK correctly using Android Studio?
Android Studio is the recommended tool for building and signing Android apps. It provides a user-friendly interface and a streamlined process for generating and managing your signing keys and keystores, as well as signing your APKs.
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Here are the steps to sign your APK correctly using Android Studio:
How to generate a signing key and keystore?
You can generate a signing key and keystore using one of the following methods:
Using the keytool command: You can use the keytool command-line tool that comes with the Java Development Kit (JDK) to generate a signing key and keystore. The syntax of the command is as follows:
keytool -genkey -v -keystore .jks -alias -keyalg RSA -keysize 2048 -validity
The command will prompt you to enter a password for the keystore and the alias, as well as some information about yourself and your app, such as your name, organization, and app's package name. The command will also generate a .jks file that contains your keystore, which you should store in a safe and accessible location.
Using the Generate Signed Bundle / APK dialog: You can use the Generate Signed Bundle / APK dialog in Android Studio to generate a signing key and keystore. The dialog can be accessed by selecting Build > Generate Signed Bundle / APK from the menu bar. The dialog will guide you through the following steps:
Select whether you want to generate a signed Android App Bundle (AAB) or a signed APK. An AAB is a file format that contains all the components of your app, but allows Google Play to optimize and deliver only the necessary parts to each device. An AAB is recommended for publishing your app on Google Play, while an APK is recommended for testing or distributing your app outside of Google Play.
Select the module that you want to sign, which is usually the app module.
Create a new signing key and keystore, or choose an existing one. If you create a new one, you will have to enter a password for the keystore and the alias, as well as some information about yourself and your app, such as your name, organization, and app's package name. You will also have to specify a location for storing your keystore file.
Select whether you want to sign your app using APK Signature Scheme v2 or v3. These are signature schemes that improve the security and performance of your app by verifying it at install time. APK Signature Scheme v3 is recommended for apps that target Android 9 (API level 28) or higher, while APK Signature Scheme v2 is recommended for apps that target lower API levels.
Select whether you want to run ProGuard on your app. ProGuard is a tool that shrinks, optimizes, and obfuscates your code, making it smaller, faster, and more difficult to reverse engineer. ProGuard is recommended for apps that contain sensitive or proprietary code, or that need to reduce their size or improve their performance.
Select the destination folder for your signed app, and click Finish. Android Studio will generate a signed AAB or APK file that you can upload to Google Play or other app stores.
How to sign your APK using the signing key and keystore?
Once you have generated a signing key and keystore, you can use them to sign your APK using one of the following methods:
Using the Generate Signed Bundle / APK dialog: You can use the Generate Signed Bundle / APK dialog in Android Studio to sign your APK using the signing key and keystore that you created or selected in the previous step. The dialog can be accessed by selecting Build > Generate Signed Bundle / APK from the menu bar. The dialog will guide you through the same steps as before, except that you will have to choose an existing signing key and keystore instead of creating a new one.
Using the Build > Generate Signed APK menu option: You can use the Build > Generate Signed APK menu option in Android Studio to sign your APK using the signing key and keystore that you created or selected in the previous step. This option is similar to the Generate Signed Bundle / APK dialog, but it only generates a signed APK, not a signed AAB. You will have to choose an existing signing key and keystore instead of creating a new one.
How to verify the signature of your APK?
After you have signed your APK, you can verify the signature of your APK using one of the following tools:
Using the apksigner tool: You can use the apksigner command-line tool that comes with the Android SDK Build Tools to verify the signature of your APK. The syntax of the command is as follows:
apksigner verify --verbose .apk
The command will output information about the signature of your APK, such as the signer's certificate, the signature scheme, and the digest algorithm. You can also use the --print-certs option to print the certificates of the signers.
Using the jarsigner tool: You can use the jarsigner command-line tool that comes with the Java Development Kit (JDK) to verify the signature of your APK. The syntax of the command is as follows:
jarsigner -verify -verbose -certs .apk
The command will output information about the signature of your APK, such as the signer's certificate, the signature scheme, and the digest algorithm.
How to sign your APK correctly using other tools?
If you prefer not to use Android Studio, you can also sign your APK correctly using other tools, such as Gradle, apksigner, or jarsigner. These tools require more manual configuration and execution, but they offer more flexibility and control over the signing process and options. Here are the steps to sign your APK correctly using other tools: How to sign your APK using Gradle?
Gradle is a build automation tool that can be used to sign your APK using a configuration file called build.gradle. This file contains instructions and parameters for building and signing your app, such as the signing key and keystore, the signature scheme, and the ProGuard settings.
To sign your APK using Gradle, you need to do the following:
Create a signing key and keystore: You can create a signing key and keystore using the keytool command or the Generate Signed Bundle / APK dialog in Android Studio, as explained in the previous section.
Configure the signingConfigs and buildTypes blocks in your app's build.gradle file: You need to configure the signingConfigs block to specify the properties of your signing key and keystore, such as the file location, the passwords, and the alias. You also need to configure the buildTypes block to specify the properties of your app's build variants, such as the debug and release versions. You can also enable or disable ProGuard and APK Signature Scheme v2 or v3 in this block. For example, your app's build.gradle file might look something like this:
android ... signingConfigs release storeFile file("my-release-key.jks") storePassword "password" keyAlias "my-alias" keyPassword "password" buildTypes release minifyEnabled true proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' signingConfig signingConfigs.release v2SigningEnabled true v3SigningEnabled true ...
Build and sign your APK using the Gradle command: You can build and sign your APK using the Gradle command-line tool that comes with Android Studio. The syntax of the command is as follows:
gradlew assemble
The parameter is the name of the build variant that you want to build and sign, such as release or debug. The command will generate a signed APK file in the app/build/outputs/apk/ directory of your project.
How to sign your APK using apksigner?
apksigner is a command-line tool that can be used to sign your APK using a signing key and keystore. This tool is part of the Android SDK Build Tools and offers more options and features than jarsigner, such as support for APK Signature Scheme v2 and v3, verification of signatures, alignment of ZIP entries, and optimization of APK files.
To sign your APK using apksigner, you need to do the following:
Create a signing key and keystore: You can create a signing key and keystore using the keytool command or the Generate Signed Bundle / APK dialog in Android Studio, as explained in the previous section.
Sign your APK using the apksigner sign command: You can sign your APK using the apksigner sign command-line tool that comes with the Android SDK Build Tools. The syntax of the command is as follows:
apksigner sign --ks .jks --out .apk .apk
The command will prompt you to enter the password for the keystore and the alias, and then generate a signed APK file with the specified output name. You can also use other options with this command, such as --ks-key-alias to specify the alias name, --v2-signing-enabled or --v3-signing-enabled to enable or disable APK Signature Scheme v2 or v3, or --key and --cert to specify separate files for the private key and public certificate instead of a keystore.
How to sign your APK using jarsigner?
jarsigner is a command-line tool that can be used to sign your APK using a signing key and keystore. This tool is part of the Java Development Kit (JDK) and offers basic functionality for signing your APK, such as support for APK Signature Scheme v1 and verification of signatures. However, this tool is not recommended for signing your APK, as it does not support APK Signature Scheme v2 or v3, which are required for apps that target Android 7.0 (API level 24) or higher.
To sign your APK using jarsigner, you need to do the following:
Create a signing key and keystore: You can create a signing key and keystore using the keytool command or the Generate Signed Bundle / APK dialog in Android Studio, as explained in the previous section.
Sign your APK using the jarsigner command: You can sign your APK using the jarsigner command-line tool that comes with the Java Development Kit (JDK). The syntax of the command is as follows:
jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore .jks .apk
The command will prompt you to enter the password for the keystore and the alias, and then generate a signed APK file with the same name as the input APK. You can also use other options with this command, such as -storetype to specify the type of the keystore, such as JKS or PKCS12.
Conclusion
Signing your APK is an essential step for publishing your app on Google Play or other app stores. It ensures that your app is authentic, secure, and compatible with various features and APIs. To sign your APK correctly, you should use the same signing key and keystore for all versions of your app, and keep them safe and consistent. You should also use Android Studio or other tools that support APK Signature Scheme v2 or v3, which are required for apps that target Android 7.0 (API level 24) or higher.
We hope this article has helped you understand how to sign your APK correctly and avoid common errors. If you have any questions or feedback, please let us know in the comments below.
FAQs
What is the difference between APK Signature Scheme v1, v2, and v3?
APK Signature Scheme v1 is the original signature scheme that signs the entire APK file, including the ZIP entries and alignment. This scheme is supported by all versions of Android, but it has some limitations, such as being vulnerable to ZIP archive attacks and requiring extra verification time and memory.
APK Signature Scheme v2 is a new signature scheme that signs only the APK file content, excluding the ZIP metadata and alignment. This scheme is supported by Android 7.0 (API level 24) or higher, and it has some advantages, such as being immune to ZIP archive attacks, allowing faster verification, and supporting key rotation.
APK Signature Scheme v3 is an extension of APK Signature Scheme v2 that adds support for key rotation without requiring a new package name or a new signing certificate. This scheme is supported by Android 9 (API level 28) or higher, and it allows developers to change their signing key without losing access to their app's data or functionality.
How can I check which signature scheme my APK uses?
You can check which signature scheme your APK uses by using the apksigner tool or the jarsigner tool, as explained in the previous section. For example, you can use the following command to check which signature scheme your APK uses:
apksigner verify --verbose .apk
The command will output information about the signature scheme of your APK, such as "Verified using v1 scheme (JAR signing): true" or "Verified using v2 scheme (APK Signature Scheme v2): true".
How can I change my app's package name?
You can change your app's package name by modifying the applicationId attribute in your app's build.gradle file. For example, you can change your app's package name from "com.example.myapp" to "com.example.myapp2" by changing the following line in your app's build.gradle file:
applicationId "com.example.myapp"
to
applicationId "com.example.myapp2"
You should also update any references to your app's package name in your manifest file, code, resources, and other files.
How can I contact Google Play support?
You can contact Google Play support by filling out and submitting the [contact form] for Google Play developers. You can also access this form by selecting Help & feedback > Contact us from the Play Console. You should provide as much information as possible about your issue, such as your app's name, package name, version code, signing key, and error message. You should also attach any relevant files, such as your APK, your original app signing key, and your upload certificate.
How can I optimize my APK size and performance?
You can optimize your APK size and performance by using various tools and techniques, such as:
Using Android App Bundle: Android App Bundle is a file format that allows Google Play to optimize and deliver only the necessary parts of your app to each device. This reduces the size of your app and improves its performance. You can generate an Android App Bundle using Android Studio or Gradle, as explained in the previous section.
Using ProGuard: ProGuard is a tool that shrinks, optimizes, and obfuscates your code, making it smaller, faster, and more difficult to reverse engineer. You can enable ProGuard in your app's build.gradle file, as explained in the previous section.
Using vector drawables: Vector drawables are images that are defined by XML files instead of bitmap files. Vector drawables can scale to any size and resolution without losing quality or increasing size. You can use vector drawables in your app by using the Vector Asset Studio in Android Studio or by adding the support library dependency to your app's build.gradle file.
Using WebP images: WebP is an image format that provides better compression than PNG or JPEG images. WebP images can reduce the size of your app and improve its loading speed. You can use WebP images in your app by converting your existing images to WebP using Android Studio or by using the cwebp command-line tool.
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