How to Use apksigner Alias to Sign Your Android Apps
If you are an Android developer, you probably know that you need to sign your apps before you can distribute them to users or upload them to Google Play. Signing your apps ensures that they are authentic and have not been tampered with by anyone else.
apksigner alias
One of the tools that you can use to sign your apps is apksigner, which is available in the Android SDK Build Tools. apksigner lets you sign APKs and confirm that their signature will be verified successfully on all versions of Android supported by that APK. It also supports key rotation, which allows you to change your signing key in case it is compromised or if you need to migrate to a stronger one.
In this article, we will explain how to use apksigner and its alias option to sign your apps. We will also show you how to change or rotate your signing key using apksigner.
How to Sign an APK Using apksigner
To sign an APK using apksigner, you need to have a keystore file and a key pair that contains your private key and certificate. A keystore file is a secure container that stores one or more key pairs. A key pair consists of a public key and a private key that are mathematically related. The public key is used to verify the signature, while the private key is used to create the signature.
You can generate a keystore file and a key pair using the keytool command, which is also part of the Android SDK Build Tools. For example, you can run the following command to create a keystore file named my-release-key.jks and a key pair with an alias of myalias:
keytool -genkey -v -keystore my-release-key.jks -alias myalias -keyalg RSA -keysize 2048 -validity 10000
The command will prompt you to enter some information about yourself and your app, such as your name, organization, and location. It will also ask you to enter a password for the keystore file and the key pair. You should keep these passwords secure and remember them, as you will need them later to sign your app.
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Once you have a keystore file and a key pair, you can use the sign command of apksigner to sign your app. You need to specify the keystore file using the --ks option and the alias of the key pair using the --ks-key-alias option. For example, you can run the following command to sign an app named my-app.apk using the keystore file and key pair that we created earlier:
apksigner sign --ks my-release-key.jks --ks-key-alias myalias my-app.apk
The command will prompt you to enter the passwords for the keystore file and the key pair. It will then sign the app in place, which overwrites the input APK file. If you want to save the signed app in a different location, you can use the --out option. For example, you can run the following command to save the signed app as my-app-signed.apk:
apksigner sign --ks my-release-key.jks --ks-key-alias myalias --out my-app-signed.apk my-app.apk
After signing your app, you can verify the signature of the APK using the verify command of apksigner. For example, you can run the following command to check if the app is signed properly and will be verified on all supported Android platforms:
apksigner verify --verbose my-app-signed.apk
The command will print a summary of the signature information and any warnings or errors that may affect the verification of the app. If the app is signed correctly, you will see a message like this:
Verifies Verified using v1 scheme (JAR signing): true Verified using v2 scheme (APK Signature Scheme v2): true Verified using v3 scheme (APK Signature Scheme v3): true Verified using v4 scheme (APK Signature Scheme v4): true Verified for SourceStamp: true Number of signers: 1
How to Change or Rotate the Signing Key
Sometimes, you may need to change or rotate your signing key for various reasons, such as:
Your signing key is lost or compromised.
Your signing key is too weak or outdated.
You want to use a different signing key for a new version of your app.
However, changing your signing key can be problematic, because devices will not accept updates that are signed with a different key than the one used for the installed app. To solve this issue, you can use the rotate command of apksigner, which allows you to create a new signing key and link it to your old one using a certificate lineage. A certificate lineage is a sequence of certificates that proves that the new key is authorized by the old one.
To use the rotate command, you need to have both the old and new keystores and aliases. You also need to provide an input file that contains the existing certificate lineage, and an output file where the new certificate lineage will be saved. For example, you can run the following command to create a new signing key and link it to your old one:
apksigner rotate --in old-lineage.txt --out new-lineage.txt --old-signer --ks old-release-key.jks --ks-key-alias oldalias --new-signer --ks new-release-key.jks --ks-key-alias newalias
The command will prompt you to enter the passwords for both keystores and aliases. It will then generate a new certificate lineage file that contains both the old and new certificates. You can use this file to sign your app with the new key and still have it verified by devices that have your app installed with the old key.
Conclusion
In this article, we have learned how to use apksigner and its alias option to sign our Android apps. We have also learned how to change or rotate our signing key using apksigner. Signing our apps is an important step to ensure their authenticity and integrity, and to prevent unauthorized modifications or installations.
Here are some tips and best practices for signing our apps with apksigner:
Use a strong and secure password for your keystore file and key pair.
Keep your keystore file and key pair in a safe location and back them up regularly.
Avoid sharing your keystore file and key pair with anyone else.
If possible, use a separate upload key for Google Play App Signing, which allows you to delegate app signing to Google Play while keeping your app signing key safe.
If you need to change or rotate your signing key, use the rotate command of apksigner to create a certificate lineage that links your old and new keys.
FAQs
What is the difference between jarsigner and apksigner?
jarsigner is a tool that is part of the Java Development Kit (JDK) that allows you to sign JAR files using digital signatures. jarsigner can also be used to sign APK files, but it only supports the v1 signature scheme, which is based on the JAR signing mechanism. jarsigner does not support the newer v2, v3, and v4 signature schemes, which are based on the APK Signature Scheme and offer better performance and security. apksigner is a tool that is part of the Android SDK Build Tools that allows you to sign APK files using any of the supported signature schemes. apksigner also supports key rotation, which jarsigner does not. Therefore, it is recommended to use apksigner instead of jarsigner to sign your APK files.
How to list the content and alias of a keystore file?
You can use the keytool command with the -list option to list the content and alias of a keystore file. For example, you can run the following command to list the content and alias of a keystore file named my-release-key.jks:
keytool -list -v -keystore my-release-key.jks
The command will prompt you to enter the password for the keystore file. It will then print the details of each entry in the keystore file, such as the alias, creation date, certificate fingerprint, and validity period.
How to sign an APK with multiple signers?
You can use the --next-signer option of apksigner to sign an APK with multiple signers. This option allows you to specify another signer after the previous one. For example, you can run the following command to sign an APK with two signers, each with their own keystore file and alias:
apksigner sign --ks signer1.jks --ks-key-alias signer1alias --next-signer --ks signer2.jks --ks-key-alias signer2alias my-app.apk
The command will prompt you to enter the passwords for both keystores and aliases. It will then sign the APK with both signers in sequence.
How to use a separate upload key for Google Play App Signing?
If you use Google Play App Signing, you can delegate app signing to Google Play while keeping your app signing key safe. You can also use a separate upload key to upload your app to Google Play, which is different from your app signing key. This way, if your upload key is compromised or lost, you can request Google Play to reset it without affecting your app signing key.
To use a separate upload key for Google Play App Signing, you need to follow these steps:
Create a new keystore file and key pair for your upload key using keytool.
Sign your app with your upload key using apksigner.
Upload your signed app to Google Play Console and enroll in Google Play App Signing.
Export your app signing certificate from Google Play Console and save it as a PEM file.
Create a certificate lineage file that links your upload key to your app signing key using apksigner rotate.
Sign your app with your upload key and certificate lineage using apksigner sign.
Upload your signed app with certificate lineage to Google Play Console.
How to recover a lost or compromised signing key?
If you lose or compromise your signing key, you may not be able to update your app or verify its signature. However, depending on your situation, you may have some options to recover or replace your signing key:
If you use Google Play App Signing, you can contact Google Play support and request them to reset your upload key or provide you with a new app signing key.
If you have a backup of your keystore file and password, you can restore it and use it to sign your app.
If you have a certificate lineage file that links your old and new keys, you can use it to sign your app with the new key and have it verified by devices that have your app installed with the old key.
If none of the above options are available, you may have to create a new app with a new package name and a new signing key, and ask your users to install it.
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