What is Android keystore file and what is it used for

Question

This is a general question  but particularly I am interested in it s use for Android  What is a keystore file  and what is it used for   Can multiple Android applications use the same keystore to sign their application  what exactly does it mean to  sign  an  apk    and what are the implications  if any  of this

User · Answer

Android Market requires you to sign all apps you publish with a certificate, using a public/private key mechanism (the certificate is signed with your private key). This provides a layer of security that prevents, among other things, remote attackers from pushing malicious updates to your application to market (all updates must be signed with the same key).

From The App-Signing Guide of the Android Developer's site:

In general, the recommended strategy for all developers is to sign all of your applications with the same certificate, throughout the expected lifespan of your applications. There are several reasons why you should do so...

Using the same key has a few benefits - One is that it's easier to share data between applications signed with the same key. Another is that it allows multiple apps signed with the same key to run in the same process, so a developer can build more "modular" applications.

User · Answer

You can find more information about the signing process on the official Android documentation here   http   developer android com guide publishing app-signing html  Yes  you can sign several applications with the same keystore  But you must remember one important thing   if you publish an app on the Play Store  you have to sign it with a non debug certificate  And if one day you want to publish an update for this app  the keystore used to sign the apk must be the same  Otherwise  you will not be able to post your update

User · Answer

The whole idea of a keytool is to sign your apk with a unique identifier indicating the source of that apk  A keystore file  from what I understand  is used for debuging so your apk has the functionality of a keytool without signing your apk for production  So yes  for debugging purposes you should be able to sign multiple apk s with a single keystore  But understand that  upon pushing to production you ll need unique keytools as identifiers for each apk you create

User · Answer

The answer I would provide is that a keystore file is to authenticate yourself to anyone who is asking  It isn t restricted to just signing  apk files  you can use it to store personal certificates  sign data to be transmitted and a whole variety of authentication   In terms of what you do with it for Android and probably what you re looking for since you mention signing apk s  it is your certificate  You are branding your application with your credentials  You can brand multiple applications with the same key  in fact  it is recommended that you use one certificate to brand multiple applications that you write  It easier to keep track of what applications belong to you   I m not sure what you mean by implications  I suppose it means that no one but the holder of your certificate can update your application  That means that if you release it into the wild  lose the cert you used to sign the application  then you cannot release updates so keep that cert safe and backed up if need be    But apart from signing apks to release into the wild  you can use it to authenticate your device to a server over SSL if you so desire   also Android related  among other functions

[android] What is Android keystore file, and what is it used for?

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