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Q: How to sign an android apk file

This was originally posted as an answer to the question "How to sign an android apk file" on stackoverflow.com.
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Here is a guide on how to manually sign an APK. It includes info about the new apk-signer introduced in build-tools 24.0.3 (10/2016)

Automated Process: #

Use this tool (uses the new apksigner from Google):

https://github.com/patrickfav/uber-apk-signer

Disclaimer: Im the developer :)

Manual Process: #

Step 1: Generate Keystore (only once) #

You need to generate a keystore once and use it to sign your unsigned apk. Use the keytool provided by the JDK found in %JAVA_HOME%/bin/

keytool -genkey -v -keystore my.keystore -keyalg RSA -keysize 2048 -validity 10000 -alias app

Step 2 or 4: Zipalign #

zipalign which is a tool provided by the Android SDK found in e.g. %ANDROID_HOME%/sdk/build-tools/24.0.2/ is a mandatory optimzation step if you want to upload the apk to the Play Store.

zipalign -p 4 my.apk my-aligned.apk

Note: when using the old jarsigner you need to zipalign AFTER signing. When using the new apksigner method you do it BEFORE signing (confusing, I know). Invoking zipalign before apksigner works fine because apksigner preserves APK alignment and compression (unlike jarsigner).

You can verify the alignment with

zipalign -c 4 my-aligned.apk

Step 3: Sign & Verify #

Using build-tools 24.0.2 and older #

Use jarsigner which, like the keytool, comes with the JDK distribution found in %JAVA_HOME%/bin/ and use it like so:

jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my.keystore my-app.apk my_alias_name

and can be verified with

jarsigner -verify -verbose my_application.apk

Using build-tools 24.0.3 and newer #

Android 7.0 introduces APK Signature Scheme v2, a new app-signing scheme that offers faster app install times and more protection against unauthorized alterations to APK files (See here and here for more details). Threfore Google implemented their own apk signer called apksigner (duh!) The script file can be found in %ANDROID_HOME%/sdk/build-tools/24.0.3/ (the .jar is in the /lib subfolder). Use it like this

apksigner sign --ks my.keystore my-app.apk --ks-key-alias alias_name

and can be verified with

apksigner verify my-app.apk

The official documentation can be found here.