frameworks_base/docs/html/guide/developing/app-signing.jd

page.title=Signing Your Applications
@jd:body

<p>The Android system requires that all installed applications be digitally
signed with a certificate whose private key is held by the application's
developer. The system uses the certificate as a means of identifying the author of
an application and establishing trust relationships between applications, rather
than for controlling which applications the user can install. The certificate
does not need to be signed by a certificate authority: it is perfectly
allowable, and typical, for Android applications to use self-signed
certificates.</p>

<p>The important points to understand about signing Android applications are:</p>

<ul>
  <li>All applications <em>must</em> be signed. The system will not install an application 
that is not signed.</li>
  <li>You can use self-signed certificates to sign your applications. No certificate authority 
is needed.</li>
  <li>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. 
  </li>
  <li>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.</li>
  <li>You can use standard tools &mdash; Keytool and Jarsigner &mdash; to generate keys and 
sign your application .apk files.</li>
</ul>

<p>The Android system will not install or run an application that is not signed appropriately. This 
applies wherever the Android system is run, whether on an actual device or on the emulator. 
For this reason, you must set up signing for your application before you will be able to 
run or debug it on an emulator or device.</p>

<p>The Android SDK tools assist you in signing your applications when debugging. Both the ADT Plugin 
for Eclipse and the Ant build tool offer two signing modes &mdash; debug mode and release mode. 

<ul>
<li>In debug mode, the build tools use the Keytool utility, included in the JDK, to create 
a keystore and key with a known alias and password. At each compilation, the tools then use 
the debug key to sign the application .apk file. Because the password is known, the tools 
don't need to prompt you for the keystore/key password each time you compile.</li>

<li>When your application is ready for release, you compile it in release signing mode. 
In this mode, the tools compile your .apk <em>without</em> signing it. You must then sign
the .apk manually &mdash; <span style="color:red">with your private key</span> &mdash; 
using Jarsigner (or similar tool). If you do not have a suitable private key already, 
you can run Keytool manually to generate your own keystore/key and then sign your 
application with Jarsigner.</li>
</ul>

<h2>Signing Strategies</h2>

<p>Some aspects of application signing may affect how you approach the development
of your application, especially if you are planning to release multiple
applications. </p>

<p>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: </p>

<ul>
<li>Application upgrade &mdash; As you release upgrades to your
application, you will want to sign the upgrades with the same certificate, if you
want users to upgrade seamlessly to the new version. When the system is 
installing an update to an application, if any of the certificates in the 
new version match any of the certificates in the old version, then the 
system allows the update. If you sign the version without using a matching
certificate, you will also need to assign a different package name to the 
application &mdash; in this case, the user installs the new version as a 
completely new application. 

<li>Application modularity &mdash; The Android system allows applications that
are signed by the same certificate to run in the same process, if the
applications so request, so that the system treats them as a single application.
In this way you can deploy your application in modules, and users can update
each of the modules independently if needed.</li>

<li>Code/data sharing through permissions &mdash; The Android system provides
signature-based permissions enforcement, so that an application can expose
functionality to another application that is signed with a specified
certificate. By signing multiple applications with the same certificate and
using signature-based permissions checks, your applications can share code and
data in a secure manner. </li>

</li>

</ul>

<p>Another important consideration in determining your signing strategy is 
how to set the validity period of the key that you will use to sign your 
applications.</p>

<ul>
<li>If you plan to support upgrades for a single application, you should ensure 
that your key has a validity period that exceeds the expected lifespan of
that application. A validity period of 25 years or more is recommended. 
When your key's validity period expires, users will no longer be
able to seamlessly upgrade to new versions of your application.</li>

<li>If you will sign multiple distinct applications with the same key, 
you should ensure that your key's validity period exceeds the expected 
lifespan of <em>all versions of all of the applications</em>, including 
dependent applications that may be added to the suite in the future. </li>

<li>If you plan to publish your application(s) on Android Market, the
key you use to sign the application(s) must have a validity period 
ending after 22 October 2033. The Market server enforces this requirement
to ensure that users can seamlessly upgrade Market applications when
new versions are available. </li>
</ul>

<p>As you design your application, keep these points in mind and make sure to
use a <a href="#cert">suitable certificate</a> to sign your applications. </p>

<h2 id="setup">Basic Setup for Signing</h2>

<p>To support the generation of a keystore and debug key, you should first make sure that 
Keytool is available to the SDK build 
tools. In most cases, you can tell the SDK build tools how to find Keytool by making sure 
that your JAVA_HOME environment variable is set and that it references a suitable JDK. 
Alternatively, you can add the JDK version of Keytool to your PATH variable.</p>

<p>If you are developing on a version of Linux that originally came with GNU Compiler for 
Java, make sure that the system is using the JDK version of Keytool, rather than the gcj 
version. If Keytool is already in your PATH, it might be pointing to a symlink at 
/usr/bin/keytool. In this case, check the symlink target to make sure that it points 
to the Keytool in the JDK.</p>

<p>If you will release your application to the public, you will also need to have
the Jarsigner tool available on your machine. Both Jarsigner and Keytool are included
in the JDK. </p>

<h2>Signing in Debug Mode</h2>

<p>The Android build tools provide a debug signing mode that makes it easier for you 
to develop and debug your application, while still meeting the Android system
requirement for signing your .apk when it is installed in the emulator or a device. </p>

<p>If you are developing in Eclipse/ADT and have set up Keytool as described
above, signing in debug mode is enabled by default. When you run or debug your
application, ADT signs the .apk for you and installs it on the emulator. No
specific action on your part is needed, provided ADT has access to Keytool.</p>

<p>If you use Ant to build your .apk files, debug signing mode 
is enabled by default, assuming that you are using a build.xml file generated by the 
activitycreator tool included in the latest SDK. When you run Ant against build.xml to 
compile your app, the build script generates a keystore/key and signs the .apk for you. 
No specific action on your part is needed.</p>

<p>Note that you can not release your application to the public if it is signed only with
the debug key. </p>

<h2>Signing for Public Release</h2>

<p>When your application is ready for release to other users, you must:</p>
<ol>
<li>Compile the application in release mode</li>
<li>Obtain a suitable private key, and then</li>
<li>Sign the application with your private key</li>
<li>Secure your private key</li>
</ol>

<p>The sections below provide information about these steps. </p>

<h3>Compiling for Release</h3>

<p>To prepare your application for release, you must first compile it in release mode. 
In release mode, the Android build tools compile your application as usual, 
but without signing it with the debug key.  </p>

<p>If you are developing in Eclipse/ADT, right-click the project in the Package 
pane and select <strong>Android Tools</strong> > <strong>Export Application 
Package</strong>. You can then specify the file location for the unsigned .apk. 
Alternatively, you can follow the "Exporting the unsigned .apk" 
link in the Manifest Editor overview page. </p>

<p>If you are using Ant, all you need to do is specify the build target 
"release" in the Ant command. For example, if you are running Ant from the 
directory containing your build.xml file, the command would look like this:</p>

<pre>$ ant release</pre>

<p>The build script compiles the application .apk without signing it. 

<p>Note that you can not release your application unsigned, or signed with the debug key.</p>

<h3 id="cert">Obtaining a Suitable Private Key</h3>

<p>In preparation for signing your application, you must first ensure that 
you have a suitable private key with which to sign. A suitable private 
key is one that:</p>

<ul>
<li>Is in your possession</li>
<li>Represents the personal, corporate, or organizational entity to be identified 
with the application</li>
<li>Has a validity period that exceeds the expected lifespan of the application
or application suite. A validity period of more than 25 years is recommended. 
<p>If you plan to publish your application(s) on Android Market, note that a 
validity period ending after 22 October 2033 is a requirement. You can not upload an
application if it is signed with a key whose validity expires before that date. 
</p></li>
<li>Is not the debug key generated by the Android SDK tools. </li>
</ul>

<p>The key may be self-signed. If you do not have a suitable key, you must 
generate one using Keytool. Make sure that you have Keytool available, as described
in <a href="#setup">Basic Setup</a>.</p>

<p>To generate a self-signed key with Keytool, use the <code>keytool</code>
command and pass any of the options listed below (and any others, as
needed). </p>

<p class="warning">Before you run Keytool, make sure to read <a
href="#secure-key">Securing Your Key</a> for a discussion of how to keep your
key secure and why doing so is critically important to you and to users. In
particular, when you are generating your key, you should select strong
passwords for both the keystore and key.</p>

<table>
<tr>
<th>Keytool Option</th>
<th>Description</th>
</tr>
<tr>
<td><code>-genkey</code></td><td>Generate a key pair (public and private
keys)</td>
</tr>
<tr>
<td><code>-v</code></td><td>Enable verbose output.</td>
</tr>
<tr>
<td><code>-keystore&nbsp;&lt;keystore-name&gt;.keystore</code></td><td>A name
for the keystore containing the private key.</td>
</tr>
<tr>
<td><code>-storepass &lt;password&gt;</code></td><td><p>A password for the
keystore.</p><p>As a security precaution, do not include this option 
in your command line unless you are working at a secure computer.
If not supplied, Keytool prompts you to enter the password. In this 
way, your password is not stored in your shell history.</p></td>
</tr>
<tr>
<td><code>-alias &lt;alias_name&gt;</code></td><td>An alias for the key.</td>
</tr>
<tr>
<td><code>-keyalg &lt;alg&gt;</code></td><td>The encryption algorithm to use 
when generating the key.</td>
</tr>
<tr>
<td><code>-dname &lt;name&gt;</code></td><td><p>A Distinguished Name that describes
who created the key. The value is used as the issuer and subject fields in the
self-signed certificate. </p><p>Note that you do not need to specify this option
in the command line. If not supplied, Jarsigner prompts you to enter each 
of the Distinguished Name fields (CN, OU, and so on).</p></td>
</tr>
<tr>
<td><code>-validity &lt;valdays&gt;</code></td><td><p>The validity period for the
key, in days. </p><p><strong>Note:</strong> A value of 9500 or greater is recommended.</p></td>
</tr>
<tr>
<td><code>-keypass &lt;password&gt;</code></td><td><p>The password for the key.</p>
<p>As a security precaution, do not include this option 
in your command line unless you are working at a secure computer.
If not supplied, Keytool prompts you to enter the password. In this 
way, your password is not stored in your shell history.</p></td>
</tr>
</table>


<p>Here's an example of a Keytool command that generates a private key:</p>

<pre>$ keytool -genkey -v -keystore my-release-key.keystore 
-alias alias_name -keyalg RSA -validity 9500</pre>

<p>Running the example command above, Keytool prompts you to provide
passwords for the keystore and key, and to provide the Distinguished
Name fields for your key. It then generates the keystore as a file called
<code>my-release-key.keystore</code>. The keystore and key are 
protected by the passwords you entered. The keystore contains 
a single key, valid for 9500 days. The alias is a name that you &mdash;
will use later, to refer to this keystore when signing your application. </p>

<p>For more information about Keytool, see the documentation at
<a
href="http://java.sun.com/j2se/1.5.0/docs/tooldocs/#security">
http://java.sun.com/j2se/1.5.0/docs/tooldocs/#security</a></p>

<h3>Signing Your Application</h3>

<p>When you are ready to actually sign your .apk for release, you can do so
using the Jarsigner tool. Make sure that you have Jarsigner available on your
machine, as described in <a href="#setup">Basic Setup</a>. Also, make sure that
the keystore containing your private key is  available.</p>

<p>To sign your application, you run Jarsigner, referencing both the
application's .apk and the keystore containing the private key with which to
sign the .apk. The table below shows the options you could use. <p>

<table>
<tr>
<th>Jarsigner Option</th>
<th>Description</th>
</tr>
<tr>
<td><code>-keystore&nbsp;&lt;keystore-name&gt;.keystore</code></td><td>The name of
the keystore containing your private key.</td>
</tr>
<tr>
<td><code>-verbose</code></td><td>Enable verbose output.</td>
</tr>
<tr>
<td><code>-storepass &lt;password&gt;</code></td><td><p>The password for the
keystore. </p><p>As a security precaution, do not include this option 
in your command line unless you are working at a secure computer.
If not supplied, Jarsigner prompts you to enter the password. In this 
way, your password is not stored in your shell history.</p></td>
</tr>
<tr>
<td><code>-keypass &lt;password&gt;</code></td><td><p>The password for the private
key. </p><p>As a security precaution, do not include this option 
in your command line unless you are working at a secure computer.
If not supplied, Jarsigner prompts you to enter the password. In this 
way, your password is not stored in your shell history.</p></td>
</tr>
</table>

<p>Here's how you would use Jarsigner to sign an application package called
<code>my_application.apk</code>, using the example keystore created above. 
</p>

<pre>$ jarsigner -verbose -keystore my-release-key.keystore 
my_application.apk alias_name</pre>

<p>Running the example command above, Jarsigner prompts you to provide
passwords for the keystore and key. It then modifies the APK 
in-place, meaning the .apk is now signed. Note that you can sign an 
APK multiple times with different keys.</p>

<p>To verify that your .apk is signed, you can use a command like this:</p>

<pre>$ jarsigner -verify my_signed.apk</pre>

<p>If the .apk is signed properly, Jarsigner prints "jar verified". 
If you want more details, you can try one of these commands:</p>

<pre>$ jarsigner -verify -verbose my_application.apk</pre>

<p>or</p>

<pre>$ jarsigner -verify -verbose -certs my_application.apk</pre>

<p>The command above, with the <code>-certs</code> option added, will show you the 
"CN=" line that describes who created the key.</p>

<p class="note">Note: if you see "CN=Android Debug", this means the .apk was
signed with the debug key generated by the Android SDK. If you intend to release
your application, you must sign it with your private key instead of the debug
key.</p>

<p>For more information about Jarsigner, see the documentation at
<a href="http://java.sun.com/j2se/1.5.0/docs/tooldocs/#security">
http://java.sun.com/j2se/1.5.0/docs/tooldocs/#security</a></p>

<h3 id="secure-key">Securing Your Private Key</h3>

<p>Maintaining the security of your private key is of critical importance, both
to you and to the user. If you allow someone to use your key, or if you leave
your keystore and passwords in an unsecured location such that a third-party
could find and use them, your authoring identity and the trust of the user
are compromised. </p>

<p>If a third party should manage to take your key without your knowledge or 
permission, that person could sign and distribute applications that maliciously
replace your authentic applications or corrupt them. Such a person could also
sign and distribute applications under your identity that attack other 
applications or the system itself, or corrupt or steal user data. </p>

<p>Your reputation as a developer entity depends on your securing your private
key properly, at all times, until the key is expired. Here are some tips for
keeping your key secure: </p>

<ul>
<li>Select strong passwords for the keystore and key.</li>
<li>When you generate your key with Keytool, <em>do not</em> supply the 
<code>-storepass</code> and <code>-keypass</code> options at the command line. 
If you do so, your passwords will be available in your shell history, 
which any user on your computer could access.</li>
<li>Similarly, when signing your applications with Jarsigner, 
<em>do not</em> supply the <code>-storepass</code> and <code>-keypass</code> 
options at the command line. </li>
<li>Do not give or lend anyone your private key, and do not let unauthorized
persons know your keystore and key passwords.</li>
</ul>

<p>In general, if you follow common-sense precautions when generating, using,
and storing your key, it will remain secure. </p>

<h2>Expiry of the Debug Certificate</h2>

<p>The self-signed certificate used to sign your application in debug mode (the default on 
Eclipse/ADT and Ant builds) will have an expiration date of 365 days from its creation date.</p>

<p>When the certificate expires, you will get a build error. On Ant builds, the error 
looks like this:</p>

<pre>debug:
[echo] Packaging bin/samples-debug.apk, and signing it with a debug key...
[exec] Debug Certificate expired on 8/4/08 3:43 PM</pre>

<p>In Eclipse/ADT, you will see a similar error in the Android console.</p>

<p>To fix this problem, simply delete the <code>debug.keystore</code> file. On Linux/Mac OSX, 
the file is stored in <code>~/.android</code>. OOn Windows XP, the file is stored in <code>
C:\Documents and Settings\&lt;user&gt;\Local Settings\Application Data\Android</code>. 
On Windows Vista, the file is stored in <code>
C:\Users\&lt;user&gt;\AppData\Local\Android</code>.</p>

<p>The next time you build, the build tools will regenerate a new keystore and debug key.</p>

<p>Note that, if your development machine is using a non-Gregorian locale, the build 
tools may erroneously generate an already-expired debug certificate, so that you get an 
error when trying to compile your application. For workaround information, see the 
troubleshooting topic <a href="{@docRoot}kb/troubleshooting.html#signingcalendar">
I&nbsp;can't&nbsp;compile my app because the build tools generated an expired debug 
certificate</a>. </p>