META-INF Files - Digests, Signature and Certificate

This section describes META-INF files in an .apk package file: MANIFEST.MF - manifest file, CERT.SF - signature file and CERT.RSA - the real signature file with certificate.

In the previous tutorial, we learned that the debug package of an Android application is automatically signed by a debug key in the "ant debug" build process. Now I am interested to how signatures are stored in package file.

1. Copy the .apk file to a .zip file:

C:\herong\HelloAndroid>copy bin\HelloAndroid-debug.apk package.zip
        1 file(s) copied.

2. Unzip "package.zip" to \herong\package folder.

3. Open the manifest file, META-INF\MANIFEST.MF, in the package folder in a text editor. You will see a list of all files in the package with their SHA1 digests (Base64 encoded strings):

Manifest-Version: 1.0
Created-By: 1.0 (Android)

Name: res/layout/main.xml
SHA1-Digest: NXEzfMpms988J98yXEUXqh9u9ug=

Name: AndroidManifest.xml
SHA1-Digest: 0f22NLU8EbmlkrUUO0GjGIIl4zU=

Name: res/drawable-mdpi/ic_launcher.png
SHA1-Digest: 7Ft/Rirt+l/JRX2KjDREScdbCZk=

Name: res/drawable-hdpi/ic_launcher.png
SHA1-Digest: Vj/qhxk8ic8FE0/kT6E3vgRJ4mE=

Name: resources.arsc
SHA1-Digest: 5kllfCdPWbdy9w3CYz9lXYfN1Do=

Name: classes.dex
SHA1-Digest: ostS2N/xSK7OaaQ4m2rCAq8iD0k=

Name: res/drawable-ldpi/ic_launcher.png
SHA1-Digest: i7vxaosoiS+9HzKB7ZgIsXMYRLY=

4. Open the signature file, META-INF\CERT.SF, in the package folder in a text editor. You will see a list of all files in the package again with their SHA1 digests again. But this time, each digest is the digest of the 3-line entry of that file in the Manifest file.

Signature-Version: 1.0
Created-By: 1.0 (Android)
SHA1-Digest-Manifest: UOE6fu4Pq1ddGXiJC5iAOkOtDVI=

Name: res/layout/main.xml
SHA1-Digest: +IKkn6R+Vr90Oy+4cVnVwXvkqXw=

Name: AndroidManifest.xml
SHA1-Digest: 8GD9vp78dBfzFq7uRbunWZs2XjU=

Name: res/drawable-mdpi/ic_launcher.png
SHA1-Digest: zSBo0hBNc4K46aIFvlD4ZmQBHcg=

Name: res/drawable-hdpi/ic_launcher.png
SHA1-Digest: YuN8HjuH/csIGA1V8jxQw62DV0A=

Name: resources.arsc
SHA1-Digest: lU1eIHhOCyd3E+nBCgPiv27Vb+M=

Name: classes.dex
SHA1-Digest: k/Tdh4GY0wZKoL/g28iE7z3uGLI=

Name: res/layout/main_original.xml
SHA1-Digest: dD4LMOZORFmtPpAZwc0R48/FAik=

Name: res/drawable-ldpi/ic_launcher.png
SHA1-Digest: edY5GhthxxpZN3rJpWsoorrticI=

5. The real signature of the package is actually stored in the META-INF\CERT.RSA file in the package folder. The CERT.RSA also contains the certificate of the public key for you to verify the signature.

6. You can use the "keytool" command to view the certificate:

C:\herong\HelloAndroid>\Progra~1\Java\jdk1.7.0_03\bin\keytool \
   -printcert -file package\META-INF\CERT.RSA

Owner: CN=Android Debug, O=Android, C=US
Issuer: CN=Android Debug, O=Android, C=US
Serial number: 4427b9db
Valid from: Sun Mar 01 14:43:33 EDT 2012 until: \
   Tue Mar 25 14:43:33 EDT 2042
Certificate fingerprints:
         MD5:  47:F7:5B:83:5E:F0:19:08:15:7D:1B:80:67:96:9A:03
         SHA1: CA:59:3A:44:F5:08:D7:43:96:E2:EE:2C:10:91:0F:86:3C:...
         SHA256: BE:29:82:5E:4A:F6:81:D4:AA:E7:2E:D8:AB:66:B4:E2:7...
94:81:08:62:D9:AE:38:66:F9:66:1F
         Signature algorithm name: SHA256withRSA
         Version: 3

Extensions:

#1: ObjectId: 2.5.29.14 Criticality=false
SubjectKeyIdentifier [
KeyIdentifier [
0000: B4 41 2F 4A 00 AF 4B E1   2A A8 C6 E8 DA 55 13 FB  .A/J..K.*...
0010: 02 64 48 87                                        .dH.
]
]

As I expected, this certificate is a self-signed certificate, which can not be verified by any root certificate authorities. I guess for debugging purpose, this is good enough.

Last update: 2015.

Table of Contents

 About This Book

 Installing JDK 1.8 on Windows System

 Installation of Android SDK R24 and Emulator

 Installing Apache Ant 1.9 on Windows System

 Developing First Android Application - HelloAndroid

 Android Application Package (APK) Files

 Android Debug Bridge (adb) Tool

 Android File Systems

 Android 4.0.3 File Systems

 AboutAndroid - Application to Retrieve System Information

 android.app.Activity Class and Activity Lifecycle

 View Objects and Layout Resource Files

 Using "adb logcat" Command for Debugging

Build Process and Package File Content

 "android create project" Command Options

 Android Project Folder Structure

 Android Application Project Build Process

 Project Build Process Done by "ant debug" Command

 Detailed Output of "ant -verbose debug" Command

 Output of "ant -verbose debug" - Android SDK R17

 "aapt" - Android Asset Packaging Tool

 "aapt package" Command - Resource Code Generation

 "javac" - Java Compilation Command

 "dx.bat --dex" Command - Converting .class Files into .dex File

 "apkbuilder" Command - Packaging and Signing .apk File

 "zipalign" Command - Aligning File Locations in .apk Package

 "aapt dump" Command - Printing Contents of .apk Package

META-INF Files - Digests, Signature and Certificate

 Building Your Own Web Browser

 Android Command Line Shell

 Samsung Galaxy Tab 3 Mini Tablet

 USB Debugging Applications on Samsung Tablet

 Android Tablet - LG-V905R

 USB Debugging Applications on LG-V905R Tablet

 Android Phone - LG-P925g

 USB Debugging Applications on LG-P925g Phone

 Outdated Tutorials

 References

 PDF Printing Version