Android application package file (APK) is the file format used to distribute and install application software and middleware onto the Google's Android operating system. To make an APK file, a program for Android is first compiled, and then all of its parts are packaged into one file. This holds all of that program's code such as (.dex files), resources, assets, certificates, and manifest file. As is the case with many file formats, APK files can have any name needed, but must end with the four character, three letter extension, .apk.[1][2][3][4]
APK files are ZIP file formatted packages based on the JAR file format, with .apk file extensions. The MIME type associated with APK files is application/vnd.android.package-archive.[5]
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An APK file is an archive that usually contains the following folders:
META-INF directory:
MANIFEST.MF: the Manifest fileCERT.RSA: The certificate of the application.CERT.SF: The list of resources and SHA-1 digest; for example:
Signature-Version: 1.0
Created-By: 1.0 (Android)
SHA1-Digest-Manifest: wxqnEAI0UA5nO5QJ8CGMwjkGGWE=
...
Name: res/layout/exchange_component_back_bottom.xml
SHA1-Digest: eACjMjESj7Zkf0cBFTZ0nqWrt7w=
...
Name: res/drawable-hdpi/icon.png
SHA1-Digest: DGEqylP8W0n0iV/ZzBx3MW0WGCA=
res: the directory containing resources not compiled into resources.arsc (see below).AndroidManifest.xml: An additional Android manifest file, describing the name, version, access rights, referenced library files for the application. This file may be in Android binary XML that can be converted into human-readable plaintext XML with tools such as AXMLPrinter2 or apktool.classes.dex: The classes compiled in the dex format understandable by the Dalvik virtual machineresources.arsc : a file containing pre-compiled resources, such as binary XML for example.
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