How to get Facebook key hash in Android?

Integrating Facebook login in an Android app requires generating a key hash to register the app with Facebook. The key hash allows Facebook to authenticate the app during login. Here is a step-by-step guide on how to get the Facebook key hash for Android.

What is a Facebook Key Hash?

A Facebook key hash is a unique identifier that is generated from your Android app’s signature key. It is a hash of the key used to sign your Android app.

When you want to integrate Facebook login in your Android app, you need to register the app on the Facebook developers dashboard. As part of the app registration process, you need to provide the key hash of your app.

This allows Facebook to verify that the request to login is coming from your legitimate Android app, and not some malicious app pretending to be your app.

Why is the Facebook Key Hash Required?

The main reason Facebook requires the key hash during registration is to prevent abuse and misuse of the Facebook login API. Some key reasons include:

Ensure requests come from legitimate apps: The key hash allows Facebook to verify that login requests originate from your actual Android app, and not some fake app.

Prevent MITM attacks: Using the key hash prevents man-in-the-middle attacks during the login process.
Link app to developer account: The key hash links your Android app to your Facebook developer account, for tracking and analytics.
Security: It provides an additional layer of security for the login process.

Overall, the key hash provides a way for Facebook to securely authenticate your app during login. It helps prevent abuse of the Facebook APIs.

When is the Facebook Key Hash Needed?

You need the Facebook key hash in the following scenarios when working with Facebook APIs on Android:

Registering a new Android app on Facebook

Adding the release hash for publishing an Android app
Enabling Facebook login in your Android app
Using other Facebook APIs and SDKs in your Android app

Essentially, anytime you need to integrate or authenticate with Facebook from an Android app, you will need the key hash.

The key hash should be generated for each Android app, and for each version of the app. So you need to regenerate it if you are releasing an update or adding more features that use Facebook.

How to Get the Key Hash for Debug and Release Builds

The general steps to get the Facebook key hash for your Android app are:

Generate the keystore for your Android app
Create a debug and release build for your app
Extract the signature key hash from the debug and release builds

Add the hashes to the Facebook developer dashboard

The detailed instructions are as follows:

1. Generate Keystore for your Android App

If you don’t already have a keystore for your app, you need to create one first. This is required to generate the signed debug and release APKs needed for the key hash.

To generate a new keystore, use the keytool command that comes with the Java JDK:

keytool -genkeypair -alias myapp -keyalg RSA -keysize 2048 -validity 10000 -keystore myapp.jks

This will generate a keystore file called myapp.jks. Make sure to save this file, as you will need it for generating the signed APKs.

2. Create Debug and Release Builds

Next, you need to create a debug and release build for your Android app, signed with the keystore generated above.

For debug build:

./gradlew assembleDebug

For release build:

  
./gradlew assembleRelease

This will generate debug and release APK files signed with your keystore.

3. Extract Key Hashes from APKs

Once you have the debug and release APK files, you can extract the key hashes from them using keytool:

For debug APK:

keytool -printcert -jarfile app-debug.apk

For release APK:

  
keytool -printcert -jarfile app-release.apk

This will print out the certificate details, including the SHA-1 and SHA-256 key hashes.

4. Add Hashes to Facebook

Finally, go to your app configuration on the Facebook for Developers site. Under Android -> Settings, add the debug and release key hashes obtained above.

That’s it! Facebook now has the valid key hashes for your app for authentication.

Automating the Key Hash Generation

Manually generating the key hashes and adding them to Facebook each time can be tedious. You can automate the process using some simple scripts.

For example, create a shell script like get_hash.sh:

#!/bin/bash

# Build debug APK
./gradlew assembleDebug

# Store debug hash in variable  
DEBUG_HASH=$(keytool -printcert -jarfile app/build/outputs/apk/debug/app-debug.apk | grep SHA1 | awk '{print $2}')

# Build release APK 
./gradlew assembleRelease 

# Store release hash in variable
RELEASE_HASH=$(keytool -printcert -jarfile app/build/outputs/apk/release/app-release.apk | grep SHA1 | awk '{print $2}')
  
# Print hashes
echo "Debug key hash:" $DEBUG_HASH
echo "Release key hash:" $RELEASE_HASH

You can then run this script whenever you need to re-generate the key hashes.

To take it a step further, you can call the Facebook Graph API after extracting the hashes to automatically register them with your app programmatically.

Troubleshooting Key Hash Issues

Here are some common issues faced when generating Facebook key hashes for Android:

App Not Registered Error

If you get an “App Not Registered” error when trying to integrate Facebook login, it likely means the key hash is incorrect or missing.

Double check that the key hash added to Facebook matches the one printed by keytool.
Try regenerating the hashes and adding them again.
Use the latest debug/release APKs.

Wrong Hash Algorithm

Make sure to use SHA-1, not SHA-256 or MD5. Facebook requires the SHA-1 hash specifically.

Multiple Hashes

If your APK has multiple signature certificates, you may need to pass all the hashes to Facebook. The keytool output will list all certificates.

Release Hash Missing

Don’t forget to generate and register the release hash as well before publishing your app.

Conclusion

Here are some key points to remember when getting Facebook key hashes for Android:

Generate a keystore for your app
Create debug and release builds signed with the keystore

Extract SHA-1 hashes from the APKs using keytool
Add both debug and release hashes to the Facebook developer dashboard
Regenerate when updating the app

Automate hash generation for convenience

Integrating Facebook login is simple once you have the valid key hashes configured. The hash acts as a fingerprint that allows Facebook to recognize your app. Following the steps outlined in this guide will ensure you have the right key hashes for a smooth Facebook integration.

Frequently Asked Questions

1. Why do I need separate debug and release hashes?

The debug and release builds are signed with different keys. So they will have different hashes. Registering both allows Facebook to validate your app in either build type.

2. Can I reuse a keystore between apps?

Yes, you can reuse a keystore to sign multiple apps. But you need to generate and provide the hash for each individual app.

3. What if I lose my keystore?

Losing the keystore will require generating a new one, which will give you a new hash. You will have to re-register the new hash with Facebook.

4. How often do I need to regenerate the hash?

You only need to regenerate the hashes when the keystore changes or you update the Facebook SDK in your app. For most apps, hashes shouldn’t change often.

5. Can I provide hashes for multiple platforms?

Yes, the Facebook developer dashboard allows you to configure hashes for Android, iOS, and desktop platforms for the same app.

Additional Resources

Here are some useful links for more information on generating Facebook key hashes for Android:

Facebook Android SDK Overview

Facebook’s developer documentation covers the full login integration process, including key hash generation. The Android documentation provides more details on signing builds and using keytool.

Example Code

Here is some sample Java code for getting the Facebook key hash programmatically on Android:

public String getFacebookKeyHash(Context context) {

  PackageInfo info;
  try {
    info = context.getPackageManager().getPackageInfo(context.getPackageName(), PackageManager.GET_SIGNATURES);
    for (Signature signature : info.signatures) {
      MessageDigest md;
      md = MessageDigest.getInstance("SHA");
      md.update(signature.toByteArray());
      return Base64.encodeToString(md.digest(), Base64.DEFAULT);
    }
  } catch (PackageManager.NameNotFoundException e) {
    Log.e("name not found", e.toString());
  } catch (NoSuchAlgorithmException e) {
    Log.e("no such an algorithm", e.toString());
  } catch (Exception e) {
    Log.e("exception", e.toString());
  }

  return null;
}

This uses the PackageManager to get the signature for the current app, computes the SHA-1 hash, and returns the Base64 encoded key hash that can be passed to Facebook.

Summary

Here are the key steps to get Facebook key hash for Android:

Generate app keystore
Create debug and release builds

Extract SHA-1 hash from both APKs
Register hashes on Facebook
Re-generate on app updates

Consider automating the process
Double check hashes before publishing app

Configuring the correct key hash is crucial for integrating Facebook APIs in your Android app. Following this guide will help you properly obtain and configure the hashes required.