Android Development

If you want to publish an Android application you first need to write it

The result of your programming will be an .APK file which is the actual program binary of your application. However, the .APK file your compiler creates can only be used with the emulator on your desktop PC or Mac. You cannot use the same .APK file to install and run your app on your Android phone (like the G1, Kogan Agora, or else).

Why is that? Well, Google wants to protect its phone users from installing and running fraudulent software on their devices. Therefore, each and every application needs to be signed with a valid certificate that ensures where the application comes from. Meaning: the developer (you!) signs the application with his/her certificate to make sure it is always traceable where the application comes from. There are a bunch of more reasons to this so lets check out what Google is saying about this topic:

The important points to understand about signing Android applications are:

• All applications must be signed. The system will not install an application that is not signed.
• You can use self-signed certificates to sign your applications. No certificate authority is needed.
• When you are ready to publish your application, you must sign it with a suitable private key. You can not publish an application that is signed with the default key generated by the SDK tools.
• The system tests a signer certificate’s expiration date only at install time. If an application’s signer certificate expires after the application is installed, the application will continue to function normally.
• You can use standard tools — Keytool and Jarsigner — to generate keys and sign your application .apk files.

3 Easy Steps for getting what you need to sign Applications
(this needs to be done once only)

1. Create a keystore with your own keys and certificates
   First of all you need to create a keystore which stores your certificate. A certificate is always created by the developer himself without any interaction from Google. This actually means that Google does not approve certificates before you can use them for signing your application. (Note: other companies like RIM, Nokia/Symbian, Windows Mobile do such things.)

   Once you installed a Java SDK you can use the default keytool application to create your own keystore. A Java SDK is installed by default on Mac OS X machines and can also be installated additionally on your Windows PC or Linux machine. If you have Java SDK running on your system just go to any prompt and type in the following:

   Windows: START»Command
   $ keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -validity 10000

   Windows: Mac: Terminal
   $ keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -validity 10000

   You will be asked to enter a password for your keystore. Choose it wisely and remember it! You will need it every time you sign an APK file. Follow the instructions and finalize the creation of your keystore.

2. Place the keys at a location that makes sense
   Choosing the right place for your keystore is quite important. Let’s imagine you write more than one application so it would not make that much sense to put this keystore into the project directory of the application you are currently working with. As I am using Mac OS X Leopard and Eclipse I got a project directory like /Users/YOUR_NAME/Documents/workspace/DialANumber. However, as mentioned before a more global approach might make so I copied the keystore to the directory:

   /Users/YOUR_NAME/Documents/workspace/androidkeys

   So we got our keystore prepared for signing now.

3. Write a short script to make your life easier
   Just to make the life easier I wrote a short script which can be used each time to sign your Android APK file. You can download it below and place it in the same directory you placed the keystore at (see point 2).

   Download: Signing Script for Easy .APK Signing

Once you have done this we are ready for signing our application!

3 Easy Steps for getting your Application signed
(this needs to be done each time you build a binary that is going to be published)

1. Build your application

   Right click your Android project in Eclipse and select Android Tools » Export Unsigned Application Package.... Follow the instructions and remember the directory your placed the .APK file at. E.g. cd /Users/YOUR_NAME/Documents/workspace/DialANumber/deploy/

2. Go to your keystore & script directory

   cd /Users/YOUR_NAME/Documents/workspace/androidkeys/

3. Sign your application
   In your androidkeys directory you need to execute:

   ./sign-mac-example.sh ../DialANumber/deploy/DialANumber.apk
Enter passphrase:

   After you entered your passphrase the application should be signed.

You can now upload your app to your server and install it on an Android phone or you can even publish it on the Android Market!

Sources:

• Android Documentation
• Anddev.org howto

P.S.: The complete signing process (the part you need to do each time you sign an app) could be integrated better into Eclipse. I hope Google improves this in future. They could add an entry like Android Tools » Export Signed Application Package... so the developer just needs to enter the passphrase in a GUI dialog. This would make everyone’s life much easier. Perhaps a bored Eclipse PlugIn developer might want to write a plugin for this? It would make many people happy I guess

Tags: android, APK, application, certificate, google, jarsigner, keytool, sign

This entry was posted on Monday, January 19th, 2009 at 9:07 am and is filed under Distribution. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.