Should Google Manage Your Keys for Games built with Unity?

We recently had a problem that caused weeks of pain and struggle and it had nothing to do with coding. It was the damn java keystore signing process that we signed up for on the Google Play Store.

The basics are that the Google Play Store requires that all APKs be digitally signed with a certificate before they can be installed. Apps must use the same certificate in order for users to be able to install new versions or updates. This is a good and secure system. No issues here.

If you lose your key you cannot distribute any updates to your app/game. This would be really bad for some companies so Google offers to keep your keys safe so that you if you did lose them you can ask to have the key sent to you which gives you authority distribute again. Yay for Google!

But our problems start here in Unity when you build your game for Android the keystore is defined on the Player Settings tab of the Build Setting (CTRL+SHIFT+B).

In the first case when running your project from Unity the package (APK) is automatically signed with a debug certificate generated by the Android SDK tools. The debug keystore and certificate are in $HOME/.android/debug.keystore.

This debug certificate is insecure by design and can’t be used on the Google Play Store for publishing an Alpha release but you can upload it for Beta releases. I think this is where we started going wrong.

When you upload an APK to the Play Store you can opt in to app signing by Google Play. They recommend it but it’s optional. If you prefer, you can continue managing your own keys.

The advantages of opting in to the Google Play Store App Signing program is that 1. You ensure that the app signing key is not lost. 2. If your app signing key is compromised only a user with an account linked to your app can manage an upload key which makes it harder to do something malicious. (If you sign in your apps are signed with an upload key proving your credentials – Google then manages your APK and assigns it the correct and valid signing key).

To quote their documentation: “When using Google Play App Signing, you will use two keys: the app signing key and the upload key. Google manages and protects the app signing key for you, and you keep the upload key and use it to sign your apps for upload to the Google Play Store.

When you use Google Play App Signing, if you lose your upload key, or if it is compromised, you can contact Google to revoke your old upload key and generate a new one. Because your app signing key is secured by Google, you can continue to upload new versions of your app as updates to the original app, even if you change upload keys.

If you lose your keystore or think it may be compromised, app signing by Google Play makes it possible to request a reset to your upload key. If you’re not enrolled in app signing by Google Play and lose your keystore, you’ll need to publish a new app with a new package name.”

Alright. Read that last bit again. It’s important and why app signing might be a really good idea. If you manage your key yourself and you lose it and want to make an update to your app then you have to publish your whole app again under a different name. Again just to drum that home … If you lose your keystore, the only solution is to upload a new instance of the app to the Google Play Store with a new key, a whole new store listing like it’s a different product, as it will not accept an APK signed with a different key.

See: https://support.google.com/googleplay/android-developer/answer/7384423?hl=en

(Manage your app signing keys) The support team only accepts key reset requests from the Play Console account owner. The account owner can fill out a form and attach the upload_certificate.pem file. Then you can update your keystores and API provider registration.

It seems easy and if you want to read funny people on the internet slagging off the Byzantine process check out the comments under this tutorial:

https://www.youtube.com/watch?v=qGoCF0Et_CU&feature=youtu.be

I was a little lost so I started looking for the help of my peers and of course from Unity.

I found a post from one poor soul who was in the same boat as me and the response from Unity Support was: “What do you want to be supported from Unity side? I see this unrelated to our build process.” So someone needs to have a little talk to that chap.

There are more than a few forum posts around this for Unity (and that last one is for andromo but the subject is the same issue).

https://answers.unity.com/questions/1434637/can-google-play-app-signing-be-used-with-unity-and.html

https://forum.unity.com/threads/android-signing.62137/

https://answers.unity.com/questions/1372982/how-i-can-sign-my-apk-with-an-google-plays-upload.html

https://stackoverflow.com/questions/50608172/unity-google-play-app-signing-issue-and-keystore

https://forums.andromo.com/discussion/1980/important-do-not-opt-in-to-google-play-app-signing

Look – and this is really the bottom line – it all got too frustrating and annoying trying to work out what the hell was going on and since I was only in my third release cycle I just opened up a new App on the Play Store and ditched the old one. But that’s just not possible for anyone who has an App out there and has no other option. So this is the process to getting that pesky key back.

In the Google Play Store you can see your App Signing Keys here:

You got your App signing certificate – this is the one that actually signs your app.

SHA-1 certificate fingerprint (above)

SHA1: A8:C0:F2:25:E6:A4:17:A3:F7:13:7B:96:37:FB:B8:59:69:72:9B:8C

And your Upload certificate – this is the one that you use to upload with your APK so that Google knows it’s you.

Your upload key is only registered with Google and is used to authenticate the identity of the app creator.

Your upload key is removed from any uploaded APKs before being sent to users.

SHA-1 certificate fingerprint (above)

SHA1: 74:5A:11:31:6E:2E:C0:DD:8C:F5:6E:65:24:5F:77:B8:2C:EA:6A:9A

In my case the upload certificate was from the default android debug keystore (that I shouldn’t have used):

C:\Program Files\Java\jdk1.8.0_111\bin>keytool.exe -list -keystore C:\Users\<user>\.android\debug.keystore

Enter keystore password:

Keystore type: JKS

Keystore provider: SUN

Your keystore contains 1 entry

androiddebugkey, 10/08/2016, PrivateKeyEntry,

Certificate fingerprint (SHA1): 74:5A:11:31:6E:2E:C0:DD:8C:F5:6E:65:24:5F:77:B8:2C:EA:6A:9A

To generate and register a new upload key, follow the instructions in the Android Studio Help Center.

https://developer.android.com/studio/publish/app-signing#generate-key

You don’t need to use Android Studio you can also do it on the command line (which is easier I think).

First generate a private key using keytool. For example:

# keytool -genkey -v -keystore my-release-key.jks -keyalg RSA -keysize 2048 -validity 10000 -alias my-alias

C:\Program Files\Java\jdk1.8.0_111\bin>keytool -genkey -v -keystore D:\ZuluOneZero\Demo-Unity-Android-key.jks -keyalg RSA -keysize 2048 -validity 10000 -alias Demo4Unity

Enter keystore password:

Re-enter new password:

What is your first and last name?

[Zulu]: ZuluOneZero

What is the name of your organizational unit?

[Unknown]: TheDogRun

What is the name of your organization?

[Unknown]: ZuluOneZero

What is the name of your City or Locality?

[Unknown]: Melbourne

What is the name of your State or Province?

[Unknown]: Victoria

What is the two-letter country code for this unit?

[Unknown]: AU

Is CN=ZuluOneZero, OU=TheDogRun, O=ZuluOneZero, L=Melbourne, ST=Victoria, C=AU correct?

[no]: yes

Generating 2,048 bit RSA key pair and self-signed certificate (SHA256withRSA) with a validity of 10,000 days

for: CN=ZuluOneZero, OU=TheDogRun, O=ZuluOneZero, L=Melbourne, ST=Victoria, C=AU

Enter key password for <Demo4Unity>

(RETURN if same as keystore password):

Re-enter new password:

[Storing D:\ZuluOneZero\Demo-Unity-Android-key.jks]

Note: keytool is located in the bin/ directory in your JDK. To locate your JDK from Android Studio, select File > Project Structure, and then click SDK Location and you will see the JDK location

C:\Program Files\Java\jdk1.8.0_111\bin\keytool.exe

(I used this one but you will have a keytool for every JDK and JRE on your machine – doesn’t matter which one you use)

Then, export the certificate for the new key to PEM format:

# keytool -export -rfc -alias <upload> -file <upload_certificate.pem> -keystore <keystore.jks>

C:\Users\<user>\AppData\Local\GitHub\mingw32\bin\openssl.exe x509 -inform der -in C:\Users\<user>\Downloads\deployment_cert.der -out D:\ZuluOneZero\deployment_cert.pem

Add the certificate to the signing keystore:

keytool -export -rfc -alias Demo4Unity -file C:\Users\roderick\Downloads\upload_cert.der -keystore D:\ZuluOneZero\Demo-Unity-Android-key.jks

C:\Program Files\Java\jdk1.8.0_111\bin>keytool -export -rfc -alias Demo4Unity -file C:\Users\roderick\Downloads\upload_cert.der -keystore D:\ZuluOneZero\Demo-Unity-Android-key.jks

Enter keystore password:

Certificate stored in file <C:\Users\roderick\Downloads\upload_cert.der>

If you want to inspect the certificates (on Windows) right click and open with Crypto Shell Extensions.

Or you can inspect the certificates like this:

C:\Program Files\Java\jdk1.8.0_111\bin>keytool.exe -printcert -file C:\Users\<user>\Downloads\upload_cert.der

Owner: CN=ZuluOneZero, OU=TheDogRun, O=ZuluOneZero, L=Melbourne, ST=Victoria, C=AU

Issuer: CN=ZuluOneZero, OU=TheDogRun, O=ZuluOneZero, L=Melbourne, ST=Victoria, C=AU

Serial number: 3e64dcd1

Valid from: Thu Sep 13 16:28:59 AEST 2018 until: Mon Jan 29 17:28:59 AEDT 2046

Certificate fingerprints:

MD5: F8:D3:CF:84:88:8E:16:EA:3D:74:F0:7E:9E:18:13:C9

SHA1: BD:1B:A2:99:05:11:0E:F6:A0:B5:1A:7B:7D:EB:01:3C:8B:A7:98:6D

SHA256: 7C:24:86:CD:58:1A:2F:74:21:B0:A6:9B:3D:DF:BC:BE:2A:15:F3:23:B9:44:7F:98:5D:8D:FB:24:98:37:82:9C

Signature algorithm name: SHA256withRSA

Version: 3

Extensions:

#1: ObjectId: 2.5.29.14 Criticality=false

SubjectKeyIdentifier [

KeyIdentifier [

0000: 21 44 48 FA 63 97 2D B0 A4 92 2B 38 41 E4 2F 7D !DH.c.-…+8A./.

0010: EA 26 E0 10 .&..

]

]

You can inspect keystores like this:

C:\Program Files\Java\jdk1.8.0_111\bin>keytool.exe -list -keystore D:\ZuluOneZero\Demo-Unity-Android-key.jks

Enter keystore password:

Keystore type: JKS

Keystore provider: SUN

Your keystore contains 1 entry

demo4unity, 13/09/2018, PrivateKeyEntry,

Certificate fingerprint (SHA1): BD:1B:A2:99:05:11:0E:F6:A0:B5:1A:7B:7D:EB:01:3C:8B:A7:98:6D

All the detail above are dummy one’s for demonstration purposes only.