How to retrieve the signature of the key used to sign an Android APK?

What is signing of an Android APK

Signing an Android APK (Android Package Kit) means applying a digital signature to the APK file using a private key to verify the authenticity and integrity of the package. The signature is created by a developer or an organization and is unique to their app.

When an app is published on the Google Play Store, the app must be signed with a certificate that verifies the identity of the developer or organization who published the app. This certificate helps ensure that the app has not been tampered with or modified since it was signed.

In addition to ensuring the authenticity of the app, signing an APK also allows the app to access system-level permissions and features, such as the ability to interact with other apps on the device or access sensitive data. Unsigned APKs cannot be installed on Android devices, and even apps with expired or revoked certificates will not be allowed to update.

In this article we will take a look at How to retrieve the signature of the key which is used to sign an Android APK.

How to retrieve the signature of the key used to sign an Android APK

Signing an Android application package (APK) is a crucial step in the process of publishing an Android app. By signing an APK, developers are able to ensure that the app is authentic and can be trusted. It also helps to protect the app from hacking and tampering. Retrieving the signature of a key used to sign an APK is a relatively simple process that can be done in a few easy steps. This guide will explain how to retrieve the signature of the key used to sign an Android APK.

Unzipping the APK file

APK is an Android application package which is composed of all the resources which are required for running any android application on a mobile device. It is basically a zip file in which all the resources required to run the application are present. To unzip the apk file we have to first rename the apk file from .apk to .zip file to change its types. Once you have changed the type of the file to .zip. Then we can simply use any zip extractor installed within our system to unzip this zip file.

Locating the signature file

Once you have unzipped the apk file on your system. The next step is to locate the signature file. To locate the signature file we have to navigate to the extracted folder. Inside that folder we have to navigate to the META-INF folder. Inside this folder we have to find a file which extends with .SF extension. It may be named as CERT.SF.

Opening that .SF file

Once you have located the .SF file. In my case it is CERT.SF, we have to simply open that file. Inside this file we will get to see the different signing keys which are being used to sign the android application.

Locating the signature of the key

Once you open a .SF file which is CERT.SF in my case. We will get to see so many keys present in that file. Inside this file we have to go to the bottom where we will get to see a key which is labeled as "X-Android-Signature". Alternatively you can search for this keyword inside your .SF file to find it.

Verify the signature

Once you have found the signature. We have to verify the signature. For verifying the signature we will require the keystore file. This keystore file is used when we are creating a signing for our application. Once you have downloaded this keystore file then you have to simply run the command as "keytool -verify" command to verify the signature of your keystore file. If the signature matches, the key which is used to sign is valid otherwise it is invalid.

Conclusion

In the above article we have taken a look at How to retrieve the signature of the key which is used to sign an Android APK file.