The OpenPGP API provides methods to execute OpenPGP operations, such as sign, encrypt, decrypt, verify, and more without user interaction from background threads. This is done by connecting your client application to a remote service provided by OpenKeychain or other OpenPGP providers.

• OpenPgpDecryptionResult and OpenPgpSignatureResult are now immutable
• Added PROGRESS_MESSENGER and DATA_LENGTH extras for ACTION_DECRYPT_VERIFY. This allows to the client app to get periodic updates for displaying a progress bar on decryption.
• Added ACTION_BACKUP
• Added special API calls for better K-9 Mail integration:
  Check for sender address matching with EXTRA_SENDER_ADDRESS and result in OpenPgpSignatureResult
  Opportunistic encryption mode with EXTRA_OPPORTUNISTIC_ENCRYPTION
  There is an external ContentProvider at org.sufficientlysecure.keychain.provider.exported for querying available keys (CAUTION: This API is not final!)

Full changelog here…

While OpenKeychain itself is GPLv3+, the API library is licensed under Apache License v2. Thus, you are allowed to also use it in closed source applications as long as you respect the Apache License v2.

Add this to your build.gradle:

repositories {
    maven { url 'https://jitpack.io' }
}

dependencies {
    implementation 'com.github.open-keychain.open-keychain:openpgp-api:v5.7.1'
}

A full working example is available in the example project. The OpenPgpApiActivity.java contains most relevant sourcecode.

OpenPgpApi contains all possible Intents and available extras.

This tutorial only covers the basics, please consult the full example for a complete overview over all methods

The API is not designed around Intents which are started via startActivityForResult. These Intent actions typically start an activity for user interaction, so they are not suitable for background tasks. Most API design decisions are explained at the bottom of this wiki page.

We will go through the basic steps to understand how this API works, following this (greatly simplified) sequence diagram:

In this diagram the client app is depicted on the left side, the OpenPGP provider (in this case OpenKeychain) is depicted on the right. The remote service is defined via the AIDL file IOpenPgpService. It contains only one exposed method which can be invoked remotely:

interface IOpenPgpService {
    Intent execute(in Intent data, in ParcelFileDescriptor input, in ParcelFileDescriptor output);
}

The interaction between the apps is done by binding from your client app to the remote service of OpenKeychain. OpenPgpServiceConnection is a helper class from the library to ease this step:

OpenPgpServiceConnection mServiceConnection;

public void onCreate(Bundle savedInstance) {
    [...]
    mServiceConnection = new OpenPgpServiceConnection(this, "org.sufficientlysecure.keychain");
    mServiceConnection.bindToService();
}

public void onDestroy() {
    [...]
    if (mServiceConnection != null) {
        mServiceConnection.unbindFromService();
    }
}

Following the sequence diagram, these steps are executed:

1. Define an Intent containing the actual PGP instructions which should be done, e.g.

   Intent data = new Intent();
   data.setAction(OpenPgpApi.ACTION_ENCRYPT);
   data.putExtra(OpenPgpApi.EXTRA_USER_IDS, new String[]{"dominik@dominikschuermann.de"});
   data.putExtra(OpenPgpApi.EXTRA_REQUEST_ASCII_ARMOR, true);

   Define an InputStream currently holding the plaintext, and an OutputStream where you want the ciphertext to be written by OpenKeychain's remote service:

   InputStream is = new ByteArrayInputStream("Hello world!".getBytes("UTF-8"));
   ByteArrayOutputStream os = new ByteArrayOutputStream();

   Using a helper class from the library, is and os are passed via ParcelFileDescriptors as input and output together with Intent data, as depicted in the sequence diagram, from the client to the remote service. Programmatically, this can be done with:

   OpenPgpApi api = new OpenPgpApi(this, mServiceConnection.getService());
   Intent result = api.executeApi(data, is, os);

2. The PGP operation is executed by OpenKeychain and the produced ciphertext is written into os which can then be accessed by the client app.

3. A result Intent is returned containing one of these result codes:

   • OpenPgpApi.RESULT_CODE_ERROR
   • OpenPgpApi.RESULT_CODE_SUCCESS
   • OpenPgpApi.RESULT_CODE_USER_INTERACTION_REQUIRED

   If RESULT_CODE_USER_INTERACTION_REQUIRED is returned, an additional PendingIntent is returned to the client, which must be used to get user input required to process the request. A PendingIntent is executed with startIntentSenderForResult, which starts an activity, originally belonging to OpenKeychain, on the task stack of the client. Only if RESULT_CODE_SUCCESS is returned, os actually contains data. A nearly complete example looks like this:

   switch (result.getIntExtra(OpenPgpApi.RESULT_CODE, OpenPgpApi.RESULT_CODE_ERROR)) {
       case OpenPgpApi.RESULT_CODE_SUCCESS: {
           try {
               Log.d(OpenPgpApi.TAG, "output: " + os.toString("UTF-8"));
           } catch (UnsupportedEncodingException e) {
               Log.e(Constants.TAG, "UnsupportedEncodingException", e);
           }
   
           if (result.hasExtra(OpenPgpApi.RESULT_SIGNATURE)) {
               OpenPgpSignatureResult sigResult
                       = result.getParcelableExtra(OpenPgpApi.RESULT_SIGNATURE);
               [...]
           }
           break;
       }
       case OpenPgpApi.RESULT_CODE_USER_INTERACTION_REQUIRED: {
           PendingIntent pi = result.getParcelableExtra(OpenPgpApi.RESULT_INTENT);
           try {
               startIntentSenderForResult(pi.getIntentSender(), 42, null, 0, 0, 0);
           } catch (IntentSender.SendIntentException e) {
               Log.e(Constants.TAG, "SendIntentException", e);
           }
           break;
       }
       case OpenPgpApi.RESULT_CODE_ERROR: {
           OpenPgpError error = result.getParcelableExtra(OpenPgpApi.RESULT_ERROR);
           [...]
           break;
       }
   }

4. Results from a PendingIntent are returned in onActivityResult of the activity, which executed startIntentSenderForResult. The returned Intent data in onActivityResult contains the original PGP operation definition and new values acquired from the user interaction. Thus, you can now execute the Intent again, like done in step 1. This time it should return with RESULT_CODE_SUCCESS because all required information has been obtained by the previous user interaction stored in this Intent.

   protected void onActivityResult(int requestCode, int resultCode, Intent data) {
       [...]
       // try again after user interaction
       if (resultCode == RESULT_OK) {
           switch (requestCode) {
               case 42: {
                   encrypt(data); // defined like in step 1
                   break;
               }
           }
       }
   }

• api.executeApi(data, is, os); is a blocking call. If you want a convenient asynchronous call, use api.executeApiAsync(data, is, os, new MyCallback([... ]));, where MyCallback is an private class implementing OpenPgpApi.IOpenPgpCallback. See OpenPgpApiActivity.java for an example.

• Using

  mServiceConnection = new OpenPgpServiceConnection(this, "org.sufficientlysecure.keychain");

  connects to OpenKeychain directly. If you want to let the user choose between OpenPGP providers, you can implement the OpenPgpAppPreference.java like done in the example app.

• To enable installing a debug and release version at the same time, the debug build of OpenKeychain uses org.sufficientlysecure.keychain.debug as a package name. Make sure you connect to the right one during development!