File extension

.apk

Android Package

.apk files are Android application packages: ZIP-based archives containing the compiled code, resources, and manifest needed to install an app on Android devices.

Known meanings

Formats and reference material for .apk

Android Package

ZIP-based installable package format for Android applications

  • binaries archive
  • Google
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Details

Format notes

APK

An APK (Android Package) is the file format used to distribute and install applications on Android. It is a ZIP archive, so it begins with the usual PK signature and can be opened with any ZIP tool, but it follows a fixed layout that the Android package installer expects.

Structure

A typical APK contains AndroidManifest.xml (stored in a compiled binary XML form), one or more classes.dex files with code for the Android Runtime, resources.arsc with compiled resource tables, the res/ and assets/ directories, optional native libraries under lib/<abi>/, and a META-INF/ directory holding signature data. Every APK must be signed before Android will install it.

Signing And Distribution

Android defines several signature schemes. The original JAR-style scheme (v1) signs individual files listed in META-INF/; later schemes (v2, v3, v4) sign the APK as a whole, with the signing block placed before the ZIP central directory, which makes tampering easier to detect and installation faster. For Google Play, developers now upload Android App Bundles (.aab) rather than APKs, and Play generates device-specific APKs from them. APKs remain the format for sideloading and for other app stores.

Preservation And Security Notes

Because an APK is just a ZIP, its content can be inspected without installing it, but decompiled or repackaged APKs lose their original signature. Sideloaded APKs from untrusted sources are a common malware vector; verify the signing certificate and use tools such as apksigner verify before installing.

Further Reading

  • Android App Bundle and APK overview: https://developer.android.com/guide/app-bundle
  • apksigner tool: https://developer.android.com/tools/apksigner
  • APK signature schemes: https://source.android.com/docs/security/features/apksigning
  • Build from the command line: https://developer.android.com/studio/build/building-cmdline