Authentication using OpenKeystore SSH API (#486)

* Implemented OpenKeystore SSH API as a new authentication option

* Fix formatting problems

Signed-off-by: Harsh Shandilya <msfjarvis@gmail.com>

* Addressed review comments.

Removed leftover debugging code.
Wrapped excessively long lines.
Added missing new parameter to Javadoc.

* Merge remote-tracking branch 'upstream/master' into gpg-ssh-key

app/build.gradle.kts

@@ -84,6 +84,7 @@ dependencies {
     implementation("com.jayway.android.robotium:robotium-solo:5.6.3")
     implementation(kotlin("stdlib-jdk8", KotlinCompilerVersion.VERSION))
     implementation("androidx.constraintlayout:constraintlayout:1.1.3")
+    implementation("org.sufficientlysecure:sshauthentication-api:1.0")
 
     // Testing-only dependencies
     androidTestImplementation("junit:junit:4.12")

app/src/main/java/com/zeapo/pwdstore/git/GitActivity.java

@@ -17,11 +17,15 @@ import android.widget.ArrayAdapter;
 import android.widget.EditText;
 import android.widget.Spinner;
 import android.widget.TextView;
+
 import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.app.AppCompatActivity;
+
 import com.zeapo.pwdstore.R;
 import com.zeapo.pwdstore.UserPreference;
+import com.zeapo.pwdstore.git.config.SshApiSessionFactory;
 import com.zeapo.pwdstore.utils.PasswordRepository;
+
 import org.apache.commons.io.FileUtils;
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.RebaseCommand;
@@ -53,6 +57,8 @@ public class GitActivity extends AppCompatActivity {
     private File localDir;
     private String hostname;
     private SharedPreferences settings;
+    private SshApiSessionFactory.IdentityBuilder identityBuilder;
+    private SshApiSessionFactory.ApiIdentity identity;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -117,8 +123,10 @@ public class GitActivity extends AppCompatActivity {
                                     connection_mode_spinner.setEnabled(true);
 
                                     // however, if we have some saved that, that's more important!
-                                    if (connectionMode.equals("ssh-key")) {
+                                    if (connectionMode.equalsIgnoreCase("ssh-key")) {
                                         connection_mode_spinner.setSelection(0);
+                                    } else if (connectionMode.equalsIgnoreCase("OpenKeychain")) {
+                                        connection_mode_spinner.setSelection(2);
                                     } else {
                                         connection_mode_spinner.setSelection(1);
                                     }
@@ -370,6 +378,16 @@ public class GitActivity extends AppCompatActivity {
         updateURI();
     }
 
+    @Override
+    protected void onDestroy() {
+        // Do not leak the service connection
+        if (identityBuilder != null) {
+            identityBuilder.close();
+            identityBuilder = null;
+        }
+        super.onDestroy();
+    }
+
     @Override
     public boolean onCreateOptionsMenu(Menu menu) {
         // Inflate the menu; this adds items to the action bar if it is present.
@@ -556,16 +574,7 @@ public class GitActivity extends AppCompatActivity {
                             (dialog, id) -> {
                                 try {
                                     FileUtils.deleteDirectory(localDir);
-                                    try {
+                                    launchGitOperation(REQUEST_CLONE);
-                                        new CloneOperation(localDir, activity)
-                                                .setCommand(hostname)
-                                                .executeAfterAuthentication(connectionMode, settings.getString("git_remote_username", "git"), new File(getFilesDir() + "/.ssh_key"));
-                                    } catch (Exception e) {
-                                        //This is what happens when jgit fails :(
-                                        //TODO Handle the diffent cases of exceptions
-                                        e.printStackTrace();
-                                        new AlertDialog.Builder(GitActivity.this).setMessage(e.getMessage()).show();
-                                    }
                                 } catch (IOException e) {
                                     //TODO Handle the exception correctly if we are unable to delete the directory...
                                     e.printStackTrace();
@@ -590,15 +599,13 @@ public class GitActivity extends AppCompatActivity {
                         new AlertDialog.Builder(GitActivity.this).setMessage(e.getMessage()).show();
                     }
                 }
-                new CloneOperation(localDir, activity)
-                        .setCommand(hostname)
-                        .executeAfterAuthentication(connectionMode, settings.getString("git_remote_username", "git"), new File(getFilesDir() + "/.ssh_key"));
             } catch (Exception e) {
                 //This is what happens when jgit fails :(
                 //TODO Handle the diffent cases of exceptions
                 e.printStackTrace();
                 new AlertDialog.Builder(this).setMessage(e.getMessage()).show();
             }
+            launchGitOperation(REQUEST_CLONE);
         }
     }
 
@@ -627,47 +634,45 @@ public class GitActivity extends AppCompatActivity {
         else {
             // check that the remote origin is here, else add it
             PasswordRepository.addRemote("origin", hostname, false);
-            GitOperation op;
+            launchGitOperation(operation);
-
-            switch (operation) {
-                case REQUEST_PULL:
-                    op = new PullOperation(localDir, activity).setCommand();
-                    break;
-                case REQUEST_PUSH:
-                    op = new PushOperation(localDir, activity).setCommand();
-                    break;
-                case REQUEST_SYNC:
-                    op = new SyncOperation(localDir, activity).setCommands();
-                    break;
-                default:
-                    Log.e(TAG, "Sync operation not recognized : " + operation);
-                    return;
-            }
-
-            try {
-                op.executeAfterAuthentication(connectionMode, settings.getString("git_remote_username", "git"), new File(getFilesDir() + "/.ssh_key"));
-            } catch (Exception e) {
-                e.printStackTrace();
-            }
         }
     }
 
-    protected void onActivityResult(int requestCode, int resultCode,
+    /**
-                                    Intent data) {
+     * Attempt to launch the requested GIT operation. Depending on the configured auth, it may not
-        if (resultCode == RESULT_CANCELED) {
+     * be possible to launch the operation immediately. In that case, this function may launch an
-            setResult(RESULT_CANCELED);
+     * intermediate activity instead, which will gather necessary information and post it back via
-            finish();
+     * onActivityResult, which will then re-call this function. This may happen multiple times,
-            return;
+     * until either an error is encountered or the operation is successfully launched.
-        }
+     *
+     * @param operation The type of GIT operation to launch
+     */
+    protected void launchGitOperation(int operation) {
+        GitOperation op;
 
-        if (resultCode == RESULT_OK) {
+        try {
-            GitOperation op;
 
-            switch (requestCode) {
+            // Before launching the operation with OpenKeychain auth, we need to issue several requests
-                case REQUEST_CLONE:
+            // to the OpenKeychain API. IdentityBuild will take care of launching the relevant intents,
-                    setResult(RESULT_OK);
+            // we just need to keep calling it until it returns a completed ApiIdentity.
-                    finish();
+            if (connectionMode.equalsIgnoreCase("OpenKeychain") && identity == null) {
+                // Lazy initialization of the IdentityBuilder
+                if (identityBuilder == null) {
+                    identityBuilder = new SshApiSessionFactory.IdentityBuilder(this);
+                }
+
+                // Try to get an ApiIdentity and bail if one is not ready yet. The builder will ensure
+                // that onActivityResult is called with operation again, which will re-invoke us here
+                identity = identityBuilder.tryBuild(operation);
+                if (identity == null)
                     return;
+            }
+
+            switch (operation) {
+                case REQUEST_CLONE:
+                    op = new CloneOperation(localDir, activity).setCommand(hostname);
+                    break;
+
                 case REQUEST_PULL:
                     op = new PullOperation(localDir, activity).setCommand();
                     break;
@@ -676,22 +681,57 @@ public class GitActivity extends AppCompatActivity {
                     op = new PushOperation(localDir, activity).setCommand();
                     break;
 
+                case REQUEST_SYNC:
+                    op = new SyncOperation(localDir, activity).setCommands();
+                    break;
+
                 case GitOperation.GET_SSH_KEY_FROM_CLONE:
                     op = new CloneOperation(localDir, activity).setCommand(hostname);
                     break;
+
+                case SshApiSessionFactory.POST_SIGNATURE:
+                    return;
+
                 default:
-                    Log.e(TAG, "Operation not recognized : " + resultCode);
+                    Log.e(TAG, "Operation not recognized : " + operation);
                     setResult(RESULT_CANCELED);
                     finish();
                     return;
             }
 
-            try {
+            op.executeAfterAuthentication(connectionMode,
-                op.executeAfterAuthentication(connectionMode, settings.getString("git_remote_username", "git"), new File(getFilesDir() + "/.ssh_key"));
+                    settings.getString("git_remote_username", "git"),
-            } catch (Exception e) {
+                    new File(getFilesDir() + "/.ssh_key"),
-                e.printStackTrace();
+                    identity);
-            }
+        } catch (Exception e) {
+            e.printStackTrace();
+            new AlertDialog.Builder(this).setMessage(e.getMessage()).show();
+        }
+    }
 
+    protected void onActivityResult(int requestCode, int resultCode,
+                                    Intent data) {
+
+        // In addition to the pre-operation-launch series of intents for OpenKeychain auth
+        // that will pass through here and back to launchGitOperation, there is one
+        // synchronous operation that happens /after/ the operation has been launched in the
+        // background thread - the actual signing of the SSH challenge. We pass through the
+        // completed signature to the ApiIdentity, which will be blocked in the other thread
+        // waiting for it.
+        if (requestCode == SshApiSessionFactory.POST_SIGNATURE && identity != null)
+            identity.postSignature(data);
+
+        if (resultCode == RESULT_CANCELED) {
+            setResult(RESULT_CANCELED);
+            finish();
+        } else if (resultCode == RESULT_OK) {
+            // If an operation has been re-queued via this mechanism, let the
+            // IdentityBuilder attempt to extract some updated state from the intent before
+            // trying to re-launch the operation.
+            if (identityBuilder != null) {
+                identityBuilder.consume(data);
+            }
+            launchGitOperation(requestCode);
         }
     }
 

app/src/main/java/com/zeapo/pwdstore/git/GitOperation.java

@@ -11,16 +11,20 @@ import android.view.View;
 import android.widget.CheckBox;
 import android.widget.EditText;
 import android.widget.LinearLayout;
+
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AlertDialog;
+
 import com.jcraft.jsch.JSch;
 import com.jcraft.jsch.JSchException;
 import com.jcraft.jsch.KeyPair;
 import com.zeapo.pwdstore.R;
 import com.zeapo.pwdstore.UserPreference;
 import com.zeapo.pwdstore.git.config.GitConfigSessionFactory;
+import com.zeapo.pwdstore.git.config.SshApiSessionFactory;
 import com.zeapo.pwdstore.git.config.SshConfigSessionFactory;
 import com.zeapo.pwdstore.utils.PasswordRepository;
+
 import org.eclipse.jgit.api.GitCommand;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.transport.JschConfigSessionFactory;
@@ -76,6 +80,18 @@ public abstract class GitOperation {
         return this;
     }
 
+    /**
+     * Sets the authentication using OpenKeystore scheme
+     *
+     * @param identity The identiy to use
+     * @return the current object
+     */
+    GitOperation setAuthentication(String username, SshApiSessionFactory.ApiIdentity identity) {
+        SshSessionFactory.setInstance(new SshApiSessionFactory(username, identity));
+        this.provider = null;
+        return this;
+    }
+
     /**
      * Executes the GitCommand in an async task
      */
@@ -86,10 +102,14 @@ public abstract class GitOperation {
      *
      * @param connectionMode the server-connection mode
      * @param username       the username
-     * @param sshKey         the ssh-key file
+     * @param sshKey         the ssh-key file to use in ssh-key connection mode
+     * @param identity       the api identity to use for auth in OpenKeychain connection mode
      */
-    public void executeAfterAuthentication(final String connectionMode, final String username, @Nullable final File sshKey) {
+    public void executeAfterAuthentication(final String connectionMode,
-        executeAfterAuthentication(connectionMode, username, sshKey, false);
+                                           final String username,
+                                           @Nullable final File sshKey,
+                                           SshApiSessionFactory.ApiIdentity identity) {
+        executeAfterAuthentication(connectionMode, username, sshKey, identity, false);
     }
 
     /**
@@ -97,10 +117,15 @@ public abstract class GitOperation {
      *
      * @param connectionMode the server-connection mode
      * @param username       the username
-     * @param sshKey         the ssh-key file
+     * @param sshKey         the ssh-key file to use in ssh-key connection mode
+     * @param identity       the api identity to use for auth in OpenKeychain connection mode
      * @param showError      show the passphrase edit text in red
      */
-    private void executeAfterAuthentication(final String connectionMode, final String username, @Nullable final File sshKey, final boolean showError) {
+    private void executeAfterAuthentication(final String connectionMode,
+                                            final String username,
+                                            @Nullable final File sshKey,
+                                            SshApiSessionFactory.ApiIdentity identity,
+                                            final boolean showError) {
         if (connectionMode.equalsIgnoreCase("ssh-key")) {
             if (sshKey == null || !sshKey.exists()) {
                 new AlertDialog.Builder(callingActivity)
@@ -153,7 +178,7 @@ public abstract class GitOperation {
                                 setAuthentication(sshKey, username, sshKeyPassphrase).execute();
                             } else {
                                 // call back the method
-                                executeAfterAuthentication(connectionMode, username, sshKey, true);
+                                executeAfterAuthentication(connectionMode, username, sshKey, identity, true);
                             }
                         } else {
                             new AlertDialog.Builder(callingActivity)
@@ -171,7 +196,7 @@ public abstract class GitOperation {
                                         } else {
                                             settings.edit().putString("ssh_key_passphrase", null).apply();
                                             // call back the method
-                                            executeAfterAuthentication(connectionMode, username, sshKey, true);
+                                            executeAfterAuthentication(connectionMode, username, sshKey, identity, true);
                                         }
                                     }).setNegativeButton(callingActivity.getResources().getString(R.string.dialog_cancel), (dialog, whichButton) -> {
                                 // Do nothing.
@@ -189,6 +214,8 @@ public abstract class GitOperation {
                             }).show();
                 }
             }
+        } else if (connectionMode.equalsIgnoreCase("OpenKeychain")) {
+            setAuthentication(username, identity).execute();
         } else {
             final EditText password = new EditText(callingActivity);
             password.setHint("Password");

app/src/main/java/com/zeapo/pwdstore/git/config/SshApiSessionFactory.java

@@ -0,0 +1,358 @@
+package com.zeapo.pwdstore.git.config;
+
+import android.app.Activity;
+import android.app.PendingIntent;
+import android.content.Intent;
+import android.content.IntentSender;
+
+import androidx.appcompat.app.AlertDialog;
+
+import com.jcraft.jsch.Identity;
+import com.jcraft.jsch.JSch;
+import com.jcraft.jsch.JSchException;
+import com.jcraft.jsch.Session;
+import com.jcraft.jsch.UserInfo;
+import com.zeapo.pwdstore.R;
+
+import org.eclipse.jgit.errors.UnsupportedCredentialItem;
+import org.eclipse.jgit.transport.CredentialItem;
+import org.eclipse.jgit.transport.CredentialsProvider;
+import org.eclipse.jgit.transport.CredentialsProviderUserInfo;
+import org.eclipse.jgit.transport.OpenSshConfig;
+import org.eclipse.jgit.transport.URIish;
+import org.eclipse.jgit.util.Base64;
+import org.eclipse.jgit.util.FS;
+import org.openintents.ssh.authentication.ISshAuthenticationService;
+import org.openintents.ssh.authentication.SshAuthenticationApi;
+import org.openintents.ssh.authentication.SshAuthenticationApiError;
+import org.openintents.ssh.authentication.SshAuthenticationConnection;
+import org.openintents.ssh.authentication.request.KeySelectionRequest;
+import org.openintents.ssh.authentication.request.Request;
+import org.openintents.ssh.authentication.request.SigningRequest;
+import org.openintents.ssh.authentication.request.SshPublicKeyRequest;
+import org.openintents.ssh.authentication.util.SshAuthenticationApiUtils;
+
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+
+public class SshApiSessionFactory extends GitConfigSessionFactory {
+    /**
+     * Intent request code indicating a completed signature that should be posted to an outstanding
+     * ApiIdentity
+     */
+    public static final int POST_SIGNATURE = 301;
+    private String username;
+    private Identity identity;
+    public SshApiSessionFactory(String username, Identity identity) {
+        this.username = username;
+        this.identity = identity;
+    }
+
+    @Override
+    protected JSch
+    getJSch(final OpenSshConfig.Host hc, FS fs) throws JSchException {
+        JSch jsch = super.getJSch(hc, fs);
+        jsch.removeAllIdentity();
+        jsch.addIdentity(identity, null);
+        return jsch;
+    }
+
+    @Override
+    protected void configure(OpenSshConfig.Host hc, Session session) {
+        session.setConfig("StrictHostKeyChecking", "no");
+        session.setConfig("PreferredAuthentications", "publickey");
+
+        CredentialsProvider provider = new CredentialsProvider() {
+            @Override
+            public boolean isInteractive() {
+                return false;
+            }
+
+            @Override
+            public boolean supports(CredentialItem... items) {
+                return true;
+            }
+
+            @Override
+            public boolean get(URIish uri, CredentialItem... items) throws UnsupportedCredentialItem {
+                for (CredentialItem item : items) {
+                    if (item instanceof CredentialItem.Username) {
+                        ((CredentialItem.Username) item).setValue(username);
+                    }
+                }
+                return true;
+            }
+        };
+        UserInfo userInfo = new CredentialsProviderUserInfo(session, provider);
+        session.setUserInfo(userInfo);
+    }
+
+    /**
+     * Helper to build up an ApiIdentity via the invocation of several pending intents that
+     * communicate with OpenKeychain. The user of this class must handle onActivityResult and
+     * keep feeding the resulting intents into the IdentityBuilder until it can successfully complete
+     * the build.
+     */
+    public static class IdentityBuilder {
+        private SshAuthenticationConnection connection;
+        private SshAuthenticationApi api;
+        private String keyId, description, alg;
+        private byte[] publicKey;
+        private Activity callingActivity;
+
+        /**
+         * Construct a new IdentityBuilder
+         *
+         * @param callingActivity Activity that will be used to launch pending intents and that will
+         *                        receive and handle the results.
+         */
+        public IdentityBuilder(Activity callingActivity) {
+            this.callingActivity = callingActivity;
+
+            List<String> providers = SshAuthenticationApiUtils.getAuthenticationProviderPackageNames(callingActivity);
+            if (providers.isEmpty())
+                throw new RuntimeException(callingActivity.getString(R.string.no_ssh_api_provider));
+
+            // TODO: Handle multiple available providers? Are there actually any in practice beyond
+            // OpenKeychain?
+            connection = new SshAuthenticationConnection(callingActivity, providers.get(0));
+        }
+
+        /**
+         * Free any resources associated with this IdentityBuilder
+         */
+        public void close() {
+            if (connection != null && connection.isConnected())
+                connection.disconnect();
+        }
+
+        /**
+         * Helper to invoke an OpenKeyshain SSH API method and correctly interpret the result.
+         *
+         * @param request     The request intent to launch
+         * @param requestCode The request code to use if a pending intent needs to be sent
+         * @return The resulting intent if the request completed immediately, or null if we had to
+         * launch a pending intent to interact with the user
+         */
+        private Intent executeApi(Request request, int requestCode) {
+            Intent result = api.executeApi(request.toIntent());
+
+            switch (result.getIntExtra(SshAuthenticationApi.EXTRA_RESULT_CODE, -1)) {
+                case SshAuthenticationApi.RESULT_CODE_ERROR:
+                    SshAuthenticationApiError error = result.getParcelableExtra(SshAuthenticationApi.EXTRA_ERROR);
+                    throw new RuntimeException(error.getMessage());
+                case SshAuthenticationApi.RESULT_CODE_SUCCESS:
+                    break;
+                case SshAuthenticationApi.RESULT_CODE_USER_INTERACTION_REQUIRED:
+                    PendingIntent pendingIntent = result.getParcelableExtra(SshAuthenticationApi.EXTRA_PENDING_INTENT);
+                    try {
+                        callingActivity.startIntentSenderForResult(pendingIntent.getIntentSender(), requestCode, null, 0, 0, 0);
+                        return null;
+                    } catch (IntentSender.SendIntentException e) {
+                        e.printStackTrace();
+                        throw new RuntimeException(callingActivity.getString(R.string.ssh_api_pending_intent_failed));
+                    }
+                default:
+                    throw new RuntimeException(callingActivity.getString(R.string.ssh_api_unknown_error));
+            }
+
+            return result;
+        }
+
+        /**
+         * Parse a given intent to see if it is the result of an OpenKeychain pending intent. If so,
+         * extract any updated state from it.
+         *
+         * @param intent The intent to inspect
+         */
+        public void consume(Intent intent) {
+            if (intent == null)
+                return;
+
+            if (intent.hasExtra(SshAuthenticationApi.EXTRA_KEY_ID)) {
+                keyId = intent.getStringExtra(SshAuthenticationApi.EXTRA_KEY_ID);
+                description = intent.getStringExtra(SshAuthenticationApi.EXTRA_KEY_DESCRIPTION);
+            }
+
+            if (intent.hasExtra(SshAuthenticationApi.EXTRA_SSH_PUBLIC_KEY)) {
+                String keyStr = intent.getStringExtra(SshAuthenticationApi.EXTRA_SSH_PUBLIC_KEY);
+                String[] keyParts = keyStr.split(" ");
+                alg = keyParts[0];
+                publicKey = Base64.decode(keyParts[1]);
+            }
+        }
+
+        /**
+         * Try to build an ApiIdentity that will perform SSH authentication via OpenKeychain.
+         *
+         * @param requestCode The request code to use if a pending intent needs to be sent
+         * @return The built identity, or null of user interaction is still required (in which case
+         * a pending intent will have already been launched)
+         */
+        public ApiIdentity tryBuild(int requestCode) {
+            // First gate, need to initiate a connection to the service and wait for it to connect.
+            if (api == null) {
+                connection.connect(new SshAuthenticationConnection.OnBound() {
+                    @Override
+                    public void onBound(ISshAuthenticationService sshAgent) {
+                        api = new SshAuthenticationApi(callingActivity, sshAgent);
+                        // We can immediately try the next phase without needing to post back
+                        // though onActivityResult
+                        tryBuild(requestCode);
+                    }
+
+                    @Override
+                    public void onError() {
+                        new AlertDialog.Builder(callingActivity).setMessage(callingActivity.getString(
+                                R.string.openkeychain_ssh_api_connect_fail)).show();
+                    }
+                });
+
+                return null;
+            }
+
+            // Second gate, need the user to select which key they want to use
+            if (keyId == null) {
+                consume(executeApi(new KeySelectionRequest(), requestCode));
+                // If we did not immediately get the result, bail for now and wait to be re-entered
+                if (keyId == null)
+                    return null;
+            }
+
+            // Third gate, need to get the public key for the selected key. This one often does not
+            // need use interaction.
+            if (publicKey == null) {
+                consume(executeApi(new SshPublicKeyRequest(keyId), requestCode));
+                // If we did not immediately get the result, bail for now and wait to be re-entered
+                if (publicKey == null)
+                    return null;
+            }
+
+            // Have everything we need for now, build the identify
+            return new ApiIdentity(keyId, description, publicKey, alg, callingActivity, api);
+        }
+    }
+
+    /**
+     * A Jsch identity that delegates key operations via the OpenKeychain SSH API
+     */
+    public static class ApiIdentity implements Identity {
+        private String keyId, description, alg;
+        private byte[] publicKey;
+        private Activity callingActivity;
+        private SshAuthenticationApi api;
+        private CountDownLatch latch;
+        private byte[] signature;
+
+        ApiIdentity(String keyId, String description, byte[] publicKey, String alg, Activity callingActivity, SshAuthenticationApi api) {
+            this.keyId = keyId;
+            this.description = description;
+            this.publicKey = publicKey;
+            this.alg = alg;
+            this.callingActivity = callingActivity;
+            this.api = api;
+        }
+
+        @Override
+        public boolean setPassphrase(byte[] passphrase) throws JSchException {
+            // We are not encrypted with a passphrase
+            return true;
+        }
+
+        @Override
+        public byte[] getPublicKeyBlob() {
+            return publicKey;
+        }
+
+        /**
+         * Helper to handle the result of an OpenKeyshain SSH API signing request
+         *
+         * @param result The result intent to handle
+         * @return The signed challenge, or null if it was not immediately available, in which
+         * case the latch has been initialized and the pending intent started
+         */
+        private byte[] handleSignResult(Intent result) {
+            switch (result.getIntExtra(SshAuthenticationApi.EXTRA_RESULT_CODE, -1)) {
+                case SshAuthenticationApi.RESULT_CODE_ERROR:
+                    SshAuthenticationApiError error = result.getParcelableExtra(SshAuthenticationApi.EXTRA_ERROR);
+                    throw new RuntimeException(error.getMessage());
+                case SshAuthenticationApi.RESULT_CODE_SUCCESS:
+                    return result.getByteArrayExtra(SshAuthenticationApi.EXTRA_SIGNATURE);
+                case SshAuthenticationApi.RESULT_CODE_USER_INTERACTION_REQUIRED:
+                    PendingIntent pendingIntent = result.getParcelableExtra(SshAuthenticationApi.EXTRA_PENDING_INTENT);
+                    try {
+                        latch = new CountDownLatch(1);
+                        callingActivity.startIntentSenderForResult(pendingIntent.getIntentSender(), POST_SIGNATURE, null, 0, 0, 0);
+                        return null;
+
+                    } catch (Exception e) {
+                        e.printStackTrace();
+                        throw new RuntimeException(callingActivity.getString(R.string.ssh_api_pending_intent_failed));
+                    }
+                default:
+                    if (result.hasExtra(SshAuthenticationApi.EXTRA_CHALLENGE))
+                        return handleSignResult(api.executeApi(result));
+                    throw new RuntimeException(callingActivity.getString(R.string.ssh_api_unknown_error));
+            }
+
+        }
+
+        @Override
+        public byte[] getSignature(byte[] data) {
+            Intent request = new SigningRequest(data, keyId, SshAuthenticationApi.SHA1).toIntent();
+            signature = handleSignResult(api.executeApi(request));
+
+            // If we did not immediately get a signature (probable), we will block on a latch until
+            // the main activity gets the intent result and posts to us.
+            if (signature == null) {
+                try {
+                    latch.await();
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+            }
+
+            return signature;
+        }
+
+
+        /**
+         * Post a signature response back to an in-progress operation using this ApiIdentity.
+         *
+         * @param data The signature data (hopefully)
+         */
+        public void postSignature(Intent data) {
+            try {
+                signature = handleSignResult(data);
+            } finally {
+                if (latch != null)
+                    latch.countDown();
+            }
+        }
+
+        @Override
+        public boolean decrypt() {
+            return true;
+        }
+
+        @Override
+        public String getAlgName() {
+            return alg;
+        }
+
+        @Override
+        public String getName() {
+            return description;
+        }
+
+        @Override
+        public boolean isEncrypted() {
+            return false;
+        }
+
+        @Override
+        public void clear() {
+
+        }
+    }
+}

app/src/main/res/values/arrays.xml

@@ -3,6 +3,7 @@
     <string-array name="connection_modes" translatable="false">
         <item>ssh-key</item>
         <item>username/password</item>
+        <item>OpenKeychain</item>
     </string-array>
     <string-array name="clone_protocols" translatable="false">
         <item>ssh://</item>

app/src/main/res/values/strings.xml

@@ -252,4 +252,8 @@
     <string name="crypto_extra_edit_hint">username: something other extra content</string>
     <string name="get_last_changed_failed">Failed to get last changed date</string>
     <string name="hotp_pending">Tap copy to calculate HOTP</string>
+    <string name="openkeychain_ssh_api_connect_fail">Failed to connect to OpenKeychain SSH API service.</string>
+    <string name="no_ssh_api_provider">No SSH API provider found. Is OpenKeychain installed?</string>
+    <string name="ssh_api_pending_intent_failed">SSH API pending intent failed</string>
+    <string name="ssh_api_unknown_error">Unknown SSH API Error</string>
 </resources>