Revert "FingerprintDialog: Use asymmetric keys"

This reverts commit 69a36a78ca293b94452c69d06c638de804815c40.

Change-Id: I50741f5f028cb16cab6fbbebe3918ae77ce93abe

7 files changed, 87 insertions, 316 deletions

diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintAuthenticationDialogFragment.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintAuthenticationDialogFragment.java
index 17df7217..b17ebb0b 100644
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintAuthenticationDialogFragment.java
+++ b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintAuthenticationDialogFragment.java
@@ -16,9 +16,6 @@
 
 package com.example.android.fingerprintdialog;
 
-import com.example.android.fingerprintdialog.server.StoreBackend;
-import com.example.android.fingerprintdialog.server.Transaction;
-
 import android.app.Activity;
 import android.app.DialogFragment;
 import android.content.SharedPreferences;
@@ -36,18 +33,6 @@ import android.widget.EditText;
 import android.widget.ImageView;
 import android.widget.TextView;
 
-import java.io.IOException;
-import java.security.KeyFactory;
-import java.security.KeyStore;
-import java.security.KeyStoreException;
-import java.security.NoSuchAlgorithmException;
-import java.security.PublicKey;
-import java.security.Signature;
-import java.security.SignatureException;
-import java.security.cert.CertificateException;
-import java.security.spec.InvalidKeySpecException;
-import java.security.spec.X509EncodedKeySpec;
-
 import javax.inject.Inject;
 
 /**
@@ -75,7 +60,6 @@ public class FingerprintAuthenticationDialogFragment extends DialogFragment
     @Inject FingerprintUiHelper.FingerprintUiHelperBuilder mFingerprintUiHelperBuilder;
     @Inject InputMethodManager mInputMethodManager;
     @Inject SharedPreferences mSharedPreferences;
-    @Inject StoreBackend mStoreBackend;
 
     @Inject
     public FingerprintAuthenticationDialogFragment() {}
@@ -87,9 +71,6 @@ public class FingerprintAuthenticationDialogFragment extends DialogFragment
         // Do not create a new Fragment when the Activity is re-created such as orientation changes.
         setRetainInstance(true);
         setStyle(DialogFragment.STYLE_NORMAL, android.R.style.Theme_Material_Light_Dialog);
-
-        // We register a new user account here. Real apps should do this with proper UIs.
-        enroll();
     }
 
     @Override
@@ -187,38 +168,11 @@ public class FingerprintAuthenticationDialogFragment extends DialogFragment
     }
 
     /**
-     * Enrolls a user to the fake backend.
-     */
-    private void enroll() {
-        try {
-            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
-            keyStore.load(null);
-            PublicKey publicKey = keyStore.getCertificate(MainActivity.KEY_NAME).getPublicKey();
-            // Provide the public key to the backend. In most cases, the key needs to be transmitted
-            // to the backend over the network, for which Key.getEncoded provides a suitable wire
-            // format (X.509 DER-encoded). The backend can then create a PublicKey instance from the
-            // X.509 encoded form using KeyFactory.generatePublic. This conversion is also currently
-            // needed on API Level 23 (Android M) due to a platform bug which prevents the use of
-            // Android Keystore public keys when their private keys require user authentication.
-            // This conversion creates a new public key which is not backed by Android Keystore and
-            // thus does not is not affected by the bug.
-            KeyFactory factory = KeyFactory.getInstance(publicKey.getAlgorithm());
-            X509EncodedKeySpec spec = new X509EncodedKeySpec(publicKey.getEncoded());
-            PublicKey verificationKey = factory.generatePublic(spec);
-            mStoreBackend.enroll("user", "password", verificationKey);
-        } catch (KeyStoreException | CertificateException | NoSuchAlgorithmException |
-                IOException | InvalidKeySpecException e) {
-            e.printStackTrace();
-        }
-    }
-
-    /**
-     * Checks whether the current entered password is correct, and dismisses the the dialog and lets
-     * the activity know about the result.
+     * Checks whether the current entered password is correct, and dismisses the the dialog and
+     * let's the activity know about the result.
      */
     private void verifyPassword() {
-        Transaction transaction = new Transaction("user", 1);
-        if (!mStoreBackend.verify(transaction, mPassword.getText().toString())) {
+        if (!checkPassword(mPassword.getText().toString())) {
             return;
         }
         if (mStage == Stage.NEW_FINGERPRINT_ENROLLED) {
@@ -229,15 +183,24 @@ public class FingerprintAuthenticationDialogFragment extends DialogFragment
 
             if (mUseFingerprintFutureCheckBox.isChecked()) {
                 // Re-create the key so that fingerprints including new ones are validated.
-                mActivity.createKeyPair();
+                mActivity.createKey();
                 mStage = Stage.FINGERPRINT;
             }
         }
         mPassword.setText("");
-        mActivity.onPurchased(null);
+        mActivity.onPurchased(false /* without Fingerprint */);
         dismiss();
     }
 
+    /**
+     * @return true if {@code password} is correct, false otherwise
+     */
+    private boolean checkPassword(String password) {
+        // Assume the password is always correct.
+        // In the real world situation, the password needs to be verified in the server side.
+        return password.length() > 0;
+    }
+
     private final Runnable mShowKeyboardRunnable = new Runnable() {
         @Override
         public void run() {
@@ -282,22 +245,8 @@ public class FingerprintAuthenticationDialogFragment extends DialogFragment
     public void onAuthenticated() {
         // Callback from FingerprintUiHelper. Let the activity know that authentication was
         // successful.
-        mPassword.setText("");
-        Signature signature = mCryptoObject.getSignature();
-        Transaction transaction = new Transaction("user", 1);
-        try {
-            signature.update(transaction.toByteArray());
-            byte[] sigBytes = signature.sign();
-            if (mStoreBackend.verify(transaction, sigBytes)) {
-                mActivity.onPurchased(sigBytes);
-                dismiss();
-            } else {
-                mActivity.onPurchaseFailed();
-                dismiss();
-            }
-        } catch (SignatureException e) {
-            throw new RuntimeException(e);
-        }
+        mActivity.onPurchased(true /* withFingerprint */);
+        dismiss();
     }
 
     @Override
diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintModule.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintModule.java
index ddfe35c3..964e1f6d 100644
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintModule.java
+++ b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/FingerprintModule.java
@@ -16,9 +16,6 @@
 
 package com.example.android.fingerprintdialog;
 
-import com.example.android.fingerprintdialog.server.StoreBackend;
-import com.example.android.fingerprintdialog.server.StoreBackendImpl;
-
 import android.app.KeyguardManager;
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -27,12 +24,14 @@ import android.preference.PreferenceManager;
 import android.security.keystore.KeyProperties;
 import android.view.inputmethod.InputMethodManager;
 
-import java.security.KeyPairGenerator;
 import java.security.KeyStore;
 import java.security.KeyStoreException;
 import java.security.NoSuchAlgorithmException;
 import java.security.NoSuchProviderException;
-import java.security.Signature;
+
+import javax.crypto.Cipher;
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
 
 import dagger.Module;
 import dagger.Provides;
@@ -77,20 +76,22 @@ public class FingerprintModule {
     }
 
     @Provides
-    public KeyPairGenerator providesKeyPairGenerator() {
+    public KeyGenerator providesKeyGenerator() {
         try {
-            return KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore");
+            return KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
         } catch (NoSuchAlgorithmException | NoSuchProviderException e) {
-            throw new RuntimeException("Failed to get an instance of KeyPairGenerator", e);
+            throw new RuntimeException("Failed to get an instance of KeyGenerator", e);
         }
     }
 
     @Provides
-    public Signature providesSignature(KeyStore keyStore) {
+    public Cipher providesCipher(KeyStore keyStore) {
         try {
-            return Signature.getInstance("SHA256withECDSA");
-        } catch (NoSuchAlgorithmException e) {
-            throw new RuntimeException("Failed to get an instance of Signature", e);
+            return Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/"
+                    + KeyProperties.BLOCK_MODE_CBC + "/"
+                    + KeyProperties.ENCRYPTION_PADDING_PKCS7);
+        } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
+            throw new RuntimeException("Failed to get an instance of Cipher", e);
         }
     }
 
@@ -103,9 +104,4 @@ public class FingerprintModule {
     public SharedPreferences providesSharedPreferences(Context context) {
         return PreferenceManager.getDefaultSharedPreferences(context);
     }
-
-    @Provides
-    public StoreBackend providesStoreBackend() {
-        return new StoreBackendImpl();
-    }
 }
diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/MainActivity.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/MainActivity.java
index caccd823..c954bfa7 100644
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/MainActivity.java
+++ b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/MainActivity.java
@@ -28,6 +28,7 @@ import android.security.keystore.KeyGenParameterSpec;
 import android.security.keystore.KeyPermanentlyInvalidatedException;
 import android.security.keystore.KeyProperties;
 import android.util.Base64;
+import android.util.Log;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
@@ -38,16 +39,17 @@ import android.widget.Toast;
 import java.io.IOException;
 import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
-import java.security.KeyPairGenerator;
 import java.security.KeyStore;
 import java.security.KeyStoreException;
 import java.security.NoSuchAlgorithmException;
-import java.security.PrivateKey;
-import java.security.Signature;
 import java.security.UnrecoverableKeyException;
 import java.security.cert.CertificateException;
-import java.security.spec.ECGenParameterSpec;
 
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.KeyGenerator;
+import javax.crypto.SecretKey;
 import javax.inject.Inject;
 
 /**
@@ -60,7 +62,7 @@ public class MainActivity extends Activity {
     private static final String DIALOG_FRAGMENT_TAG = "myFragment";
     private static final String SECRET_MESSAGE = "Very secret message";
     /** Alias for our key in the Android Key Store */
-    public static final String KEY_NAME = "my_key";
+    private static final String KEY_NAME = "my_key";
 
     private static final int FINGERPRINT_PERMISSION_REQUEST_CODE = 0;
 
@@ -68,8 +70,8 @@ public class MainActivity extends Activity {
     @Inject FingerprintManager mFingerprintManager;
     @Inject FingerprintAuthenticationDialogFragment mFragment;
     @Inject KeyStore mKeyStore;
-    @Inject KeyPairGenerator mKeyPairGenerator;
-    @Inject Signature mSignature;
+    @Inject KeyGenerator mKeyGenerator;
+    @Inject Cipher mCipher;
     @Inject SharedPreferences mSharedPreferences;
 
     @Override
@@ -104,7 +106,7 @@ public class MainActivity extends Activity {
                         Toast.LENGTH_LONG).show();
                 return;
             }
-            createKeyPair();
+            createKey();
             purchaseButton.setEnabled(true);
             purchaseButton.setOnClickListener(new View.OnClickListener() {
                 @Override
@@ -114,11 +116,11 @@ public class MainActivity extends Activity {
 
                     // Set up the crypto object for later. The object will be authenticated by use
                     // of the fingerprint.
-                    if (initSignature()) {
+                    if (initCipher()) {
 
                         // Show the fingerprint dialog. The user has the option to use the fingerprint with
                         // crypto, or you can fall back to using a server-side verified password.
-                        mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mSignature));
+                        mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mCipher));
                         boolean useFingerprintPreference = mSharedPreferences
                                 .getBoolean(getString(R.string.use_fingerprint_to_authenticate_key),
                                         true);
@@ -135,6 +137,7 @@ public class MainActivity extends Activity {
                         // enrolled. Thus show the dialog to authenticate with their password first
                         // and ask the user if they want to authenticate with fingerprints in the
                         // future
+                        mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mCipher));
                         mFragment.setStage(
                                 FingerprintAuthenticationDialogFragment.Stage.NEW_FINGERPRINT_ENROLLED);
                         mFragment.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
@@ -145,18 +148,18 @@ public class MainActivity extends Activity {
     }
 
     /**
-     * Initialize the {@link Signature} instance with the created key in the
-     * {@link #createKeyPair()} method.
+     * Initialize the {@link Cipher} instance with the created key in the {@link #createKey()}
+     * method.
      *
      * @return {@code true} if initialization is successful, {@code false} if the lock screen has
      * been disabled or reset after the key was generated, or if a fingerprint got enrolled after
      * the key was generated.
      */
-    private boolean initSignature() {
+    private boolean initCipher() {
         try {
             mKeyStore.load(null);
-            PrivateKey key = (PrivateKey) mKeyStore.getKey(KEY_NAME, null);
-            mSignature.initSign(key);
+            SecretKey key = (SecretKey) mKeyStore.getKey(KEY_NAME, null);
+            mCipher.init(Cipher.ENCRYPT_MODE, key);
             return true;
         } catch (KeyPermanentlyInvalidatedException e) {
             return false;
@@ -166,12 +169,15 @@ public class MainActivity extends Activity {
         }
     }
 
-    public void onPurchased(byte[] signature) {
-        showConfirmation(signature);
-    }
-
-    public void onPurchaseFailed() {
-        Toast.makeText(this, R.string.purchase_fail, Toast.LENGTH_SHORT).show();
+    public void onPurchased(boolean withFingerprint) {
+        if (withFingerprint) {
+            // If the user has authenticated with fingerprint, verify that using cryptography and
+            // then show the confirmation message.
+            tryEncrypt();
+        } else {
+            // Authentication happened with backup password. Just show the confirmation message.
+            showConfirmation(null);
+        }
     }
 
     // Show confirmation, if fingerprint was used show crypto information.
@@ -185,27 +191,44 @@ public class MainActivity extends Activity {
     }
 
     /**
-     * Generates an asymmetric key pair in the Android Keystore. Every use of the private key must
-     * be authorized by the user authenticating with fingerprint. Public key use is unrestricted.
+     * Tries to encrypt some data with the generated key in {@link #createKey} which is
+     * only works if the user has just authenticated via fingerprint.
+     */
+    private void tryEncrypt() {
+        try {
+            byte[] encrypted = mCipher.doFinal(SECRET_MESSAGE.getBytes());
+            showConfirmation(encrypted);
+        } catch (BadPaddingException | IllegalBlockSizeException e) {
+            Toast.makeText(this, "Failed to encrypt the data with the generated key. "
+                    + "Retry the purchase", Toast.LENGTH_LONG).show();
+            Log.e(TAG, "Failed to encrypt the data with the generated key." + e.getMessage());
+        }
+    }
+
+    /**
+     * Creates a symmetric key in the Android Key Store which can only be used after the user has
+     * authenticated with fingerprint.
      */
-    public void createKeyPair() {
+    public void createKey() {
         // The enrolling flow for fingerprint. This is where you ask the user to set up fingerprint
         // for your flow. Use of keys is necessary if you need to know if the set of
         // enrolled fingerprints has changed.
         try {
+            mKeyStore.load(null);
             // Set the alias of the entry in Android KeyStore where the key will appear
             // and the constrains (purposes) in the constructor of the Builder
-            mKeyPairGenerator.initialize(
-                    new KeyGenParameterSpec.Builder(KEY_NAME,
-                            KeyProperties.PURPOSE_SIGN)
-                            .setDigests(KeyProperties.DIGEST_SHA256)
-                            .setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1"))
-                            // Require the user to authenticate with a fingerprint to authorize
-                            // every use of the private key
-                            .setUserAuthenticationRequired(true)
-                            .build());
-            mKeyPairGenerator.generateKeyPair();
-        } catch (InvalidAlgorithmParameterException e) {
+            mKeyGenerator.init(new KeyGenParameterSpec.Builder(KEY_NAME,
+                    KeyProperties.PURPOSE_ENCRYPT |
+                            KeyProperties.PURPOSE_DECRYPT)
+                    .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
+                            // Require the user to authenticate with a fingerprint to authorize every use
+                            // of the key
+                    .setUserAuthenticationRequired(true)
+                    .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7)
+                    .build());
+            mKeyGenerator.generateKey();
+        } catch (NoSuchAlgorithmException | InvalidAlgorithmParameterException
+                | CertificateException | IOException e) {
             throw new RuntimeException(e);
         }
     }
diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackend.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackend.java
deleted file mode 100644
index 5ecfa9e7..00000000
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackend.java
+++ /dev/null
@@ -1,61 +0,0 @@
-/*
- * Copyright (C) 2015 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License
- */
-
-package com.example.android.fingerprintdialog.server;
-
-import java.security.PublicKey;
-
-/**
- * An interface that defines the methods required for the store backend.
- */
-public interface StoreBackend {
-
-    /**
-     * Verifies the authenticity of the provided transaction by confirming that it was signed with
-     * the private key enrolled for the userId.
-     *
-     * @param transaction          the contents of the purchase transaction, its contents are
-     *                             signed
-     *                             by the
-     *                             private key in the client side.
-     * @param transactionSignature the signature of the transaction's contents.
-     * @return true if the signedSignature was verified, false otherwise. If this method returns
-     * true, the server can consider the transaction is successful.
-     */
-    boolean verify(Transaction transaction, byte[] transactionSignature);
-
-    /**
-     * Verifies the authenticity of the provided transaction by password.
-     *
-     * @param transaction the contents of the purchase transaction, its contents are signed by the
-     *                    private key in the client side.
-     * @param password    the password for the user associated with the {@code transaction}.
-     * @return true if the password is verified.
-     */
-    boolean verify(Transaction transaction, String password);
-
-    /**
-     * Enrolls a public key associated with the userId
-     *
-     * @param userId    the unique ID of the user within the app including server side
-     *                  implementation
-     * @param password  the password for the user for the server side
-     * @param publicKey the public key object to verify the signature from the user
-     * @return true if the enrollment was successful, false otherwise
-     */
-    boolean enroll(String userId, String password, PublicKey publicKey);
-
-}
diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackendImpl.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackendImpl.java
deleted file mode 100644
index 986479e0..00000000
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/StoreBackendImpl.java
+++ /dev/null
@@ -1,69 +0,0 @@
-/*
- * Copyright (C) 2015 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License
- */
-
-package com.example.android.fingerprintdialog.server;
-
-
-import java.security.InvalidKeyException;
-import java.security.NoSuchAlgorithmException;
-import java.security.PublicKey;
-import java.security.Signature;
-import java.security.SignatureException;
-import java.util.HashMap;
-import java.util.Map;
-
-/**
- * A fake backend implementation of {@link StoreBackend}.
- */
-public class StoreBackendImpl implements StoreBackend {
-
-    private final Map<String, PublicKey> mPublicKeys = new HashMap<>();
-
-    @Override
-    public boolean verify(Transaction transaction, byte[] transactionSignature) {
-        try {
-            PublicKey publicKey = mPublicKeys.get(transaction.getUserId());
-            Signature verificationFunction = Signature.getInstance("SHA256withECDSA");
-            verificationFunction.initVerify(publicKey);
-            verificationFunction.update(transaction.toByteArray());
-            if (verificationFunction.verify(transactionSignature)) {
-                // Transaction is verified with the public key associated with the user
-                // Do some post purchase processing in the server
-                return true;
-            }
-        } catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
-            // In a real world, better to send some error message to the user
-        }
-        return false;
-    }
-
-    @Override
-    public boolean verify(Transaction transaction, String password) {
-        // As this is just a sample, we always assume that the password is right.
-        return true;
-    }
-
-    @Override
-    public boolean enroll(String userId, String password, PublicKey publicKey) {
-        if (publicKey != null) {
-            mPublicKeys.put(userId, publicKey);
-        }
-        // We just ignore the provided password here, but in real life, it is registered to the
-        // backend.
-        return true;
-    }
-
-}
diff --git a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/Transaction.java b/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/Transaction.java
deleted file mode 100644
index 724102ec..00000000
--- a/security/FingerprintDialog/Application/src/main/java/com/example/android/fingerprintdialog/server/Transaction.java
+++ /dev/null
@@ -1,66 +0,0 @@
-/*
- * Copyright (C) 2015 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License
- */
-
-package com.example.android.fingerprintdialog.server;
-
-import java.io.ByteArrayOutputStream;
-import java.io.DataOutputStream;
-import java.io.IOException;
-
-/**
- * An entity that represents a single transaction (purchase) of an item.
- */
-public class Transaction {
-
-    /** The unique ID of the item of the purchase */
-    private final Long mItemId;
-
-    /** The unique user ID who made the transaction */
-    private final String mUserId;
-
-    public Transaction(String userId, long itemId) {
-        mItemId = itemId;
-        mUserId = userId;
-    }
-
-    public String getUserId() {
-        return mUserId;
-    }
-
-    public byte[] toByteArray() {
-        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
-        DataOutputStream dataOutputStream = null;
-        try {
-            dataOutputStream = new DataOutputStream(byteArrayOutputStream);
-            dataOutputStream.writeLong(mItemId);
-            dataOutputStream.writeUTF(mUserId);
-            return byteArrayOutputStream.toByteArray();
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        } finally {
-            try {
-                if (dataOutputStream != null) {
-                    dataOutputStream.close();
-                }
-            } catch (IOException ignore) {
-            }
-            try {
-                byteArrayOutputStream.close();
-            } catch (IOException ignore) {
-            }
-        }
-    }
-}
diff --git a/security/FingerprintDialog/Application/src/main/res/values/strings.xml b/security/FingerprintDialog/Application/src/main/res/values/strings.xml
index f44c06d6..9f5a6fd1 100644
--- a/security/FingerprintDialog/Application/src/main/res/values/strings.xml
+++ b/security/FingerprintDialog/Application/src/main/res/values/strings.xml
@@ -31,7 +31,6 @@
     <string name="item_price">$62.68</string>
     <string name="item_description">Mesh backpack in white. Black textile trim throughout.</string>
     <string name="purchase_done">Purchase successful</string>
-    <string name="purchase_fail">Purchase failed</string>
     <string name="new_fingerprint_enrolled_description">A new fingerprint was added to this device, so your password is required.</string>
     <string name="use_fingerprint_in_future">Use fingerprint in the future</string>
     <string name="use_fingerprint_to_authenticate_title">Use fingerprint to authenticate</string>