From f59ea3b54ed9c3106c791c13ff50468606651c5b Mon Sep 17 00:00:00 2001
From: Kenny Root <kroot@google.com>
Date: Wed, 17 Apr 2013 13:29:18 -0700
Subject: [PATCH] Add Android KeyStore API demo

Adds a sample application which uses the AndroidKeyStore and
KeyPairGenerator for AndroidKeyStore.

Bug: 8608817
Change-Id: Iec78a74461dc259e4080ed1fab7d923593fcdf75
---
 samples/ApiDemos/AndroidManifest.xml          |   7 +
 .../ApiDemos/res/layout/keystore_usage.xml    | 192 +++++++
 samples/ApiDemos/res/values/strings.xml       |  17 +
 .../android/apis/security/KeyStoreUsage.java  | 526 ++++++++++++++++++
 4 files changed, 742 insertions(+)
 create mode 100644 samples/ApiDemos/res/layout/keystore_usage.xml
 create mode 100644 samples/ApiDemos/src/com/example/android/apis/security/KeyStoreUsage.java

diff --git a/samples/ApiDemos/AndroidManifest.xml b/samples/ApiDemos/AndroidManifest.xml
index 8c58bb7a6..34464a0f6 100644
--- a/samples/ApiDemos/AndroidManifest.xml
+++ b/samples/ApiDemos/AndroidManifest.xml
@@ -2907,6 +2907,13 @@
             </intent-filter>
         </activity>
 
+        <activity android:name=".security.KeyStoreUsage" android:label="Security/KeyStore"
+            android:windowSoftInputMode="adjustPan">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.SAMPLE_CODE" />
+            </intent-filter>
+        </activity>
     </application>
 
     <instrumentation android:name=".app.LocalSampleInstrumentation"
diff --git a/samples/ApiDemos/res/layout/keystore_usage.xml b/samples/ApiDemos/res/layout/keystore_usage.xml
new file mode 100644
index 000000000..2bf784555
--- /dev/null
+++ b/samples/ApiDemos/res/layout/keystore_usage.xml
@@ -0,0 +1,192 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+     Copyright 2013 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.
+-->
+
+<!--
+     Layout for using the AndroidKeyStore provider.
+     See src/com/android/sdk/security/AndroidKeyStoreUsage.java
+-->
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/LinearLayout1"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:orientation="vertical"
+    android:padding="6dip" >
+
+    <RelativeLayout
+        android:id="@+id/entries_list_group"
+        android:layout_width="fill_parent"
+        android:layout_height="0dp"
+        android:layout_marginBottom="12dp"
+        android:layout_weight="1" >
+
+        <TextView
+            android:id="@+id/entries_list_label"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginLeft="12dp"
+            android:layout_marginTop="12dp"
+            android:text="@string/keystore_entries_list" />
+
+        <ListView
+            android:id="@+id/entries_list"
+            android:layout_width="fill_parent"
+            android:layout_height="wrap_content"
+            android:layout_alignLeft="@+id/entries_list_label"
+            android:layout_below="@+id/entries_list_label"
+            android:layout_marginBottom="12dp"
+            android:choiceMode="singleChoice" >
+
+            <requestFocus />
+        </ListView>
+
+    </RelativeLayout>
+
+    <RelativeLayout
+        android:id="@+id/sign_group"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="12dp"
+        android:layout_marginTop="12dp" >
+
+        <TextView
+            android:id="@+id/key_ops_header"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignParentLeft="true"
+            android:layout_alignParentTop="true"
+            android:layout_marginBottom="6dp"
+            android:text="@string/keystore_key_ops_header"
+            android:textAppearance="?android:attr/textAppearanceMedium" />
+
+        <TextView
+            android:id="@+id/plaintext_label"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignLeft="@id/key_ops_header"
+            android:layout_below="@id/key_ops_header"
+            android:layout_marginLeft="6dp"
+            android:text="@string/keystore_plaintext" />
+
+        <EditText
+            android:id="@+id/plaintext"
+            android:layout_width="fill_parent"
+            android:layout_height="wrap_content"
+            android:layout_alignBaseline="@+id/plaintext_label"
+            android:layout_alignParentRight="true"
+            android:layout_below="@+id/key_ops_header"
+            android:layout_toRightOf="@id/plaintext_label"
+            android:ems="10"
+            android:maxLines="1" />
+
+        <TextView
+            android:id="@+id/ciphertext_label"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignLeft="@id/plaintext_label"
+            android:layout_below="@+id/plaintext"
+            android:text="@string/keystore_ciphertext" />
+
+        <EditText
+            android:id="@+id/ciphertext"
+            android:layout_width="fill_parent"
+            android:layout_height="wrap_content"
+            android:layout_alignBaseline="@+id/ciphertext_label"
+            android:layout_alignParentRight="true"
+            android:layout_below="@+id/plaintext"
+            android:layout_toRightOf="@id/ciphertext_label"
+            android:maxLines="1" />
+
+        <LinearLayout
+            android:layout_width="fill_parent"
+            android:layout_height="wrap_content"
+            android:layout_alignLeft="@id/plaintext_label"
+            android:layout_below="@+id/ciphertext" >
+
+            <Button
+                android:id="@+id/sign_button"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_weight="1"
+                android:enabled="false"
+                android:text="@string/keystore_sign" />
+
+            <Button
+                android:id="@+id/verify_button"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_weight="1"
+                android:enabled="false"
+                android:text="@string/keystore_verify" />
+
+            <Button
+                android:id="@+id/delete_button"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_weight="1"
+                android:enabled="false"
+                android:text="@string/keystore_delete" />
+
+        </LinearLayout>
+    </RelativeLayout>
+
+    <RelativeLayout
+        android:id="@+id/generate_group"
+        android:layout_width="fill_parent"
+        android:layout_height="wrap_content"
+        android:layout_gravity="bottom"
+        android:layout_marginTop="12dp" >
+
+        <TextView
+            android:id="@+id/generating_header"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignParentLeft="true"
+            android:layout_alignParentTop="true"
+            android:text="@string/keystore_generating_header"
+            android:layout_marginBottom="6dp"
+            android:textAppearance="?android:attr/textAppearanceMedium" />
+
+        <TextView
+            android:id="@+id/entry_name_label"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_below="@+id/generating_header"
+            android:layout_marginBottom="12dp"
+            android:layout_marginLeft="6dp"
+            android:layout_alignLeft="@id/generating_header"
+            android:text="@string/keystore_entry_alias" />
+
+        <Button
+            android:id="@+id/generate_button"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignLeft="@id/entry_name_label"
+            android:layout_below="@+id/entry_name"
+            android:text="@string/keystore_generate" />
+
+        <EditText
+            android:id="@+id/entry_name"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_alignBaseline="@+id/entry_name_label"
+            android:layout_alignParentRight="true"
+            android:layout_marginBottom="12dp"
+            android:layout_toRightOf="@+id/entry_name_label"
+            android:ems="10" />
+    </RelativeLayout>
+
+</LinearLayout>
\ No newline at end of file
diff --git a/samples/ApiDemos/res/values/strings.xml b/samples/ApiDemos/res/values/strings.xml
index 0364867e7..5a1df82de 100644
--- a/samples/ApiDemos/res/values/strings.xml
+++ b/samples/ApiDemos/res/values/strings.xml
@@ -1464,4 +1464,21 @@
     <string name="task_complete">is complete</string>
     <string name="task_not_complete">is not complete</string>
 
+    <!-- =========================== -->
+    <!--  Security API demo strings  -->
+    <!-- =========================== --> <skip />
+
+    <string name="keystore_entries_list">List of entries:</string>
+
+    <string name="keystore_key_ops_header">Key operations</string>
+    <string name="keystore_plaintext">Plaintext:</string>
+    <string name="keystore_ciphertext">Ciphertext:</string>
+    <string name="keystore_sign">Sign</string>
+    <string name="keystore_verify">Verify</string>
+    <string name="keystore_delete">Delete</string>
+
+    <string name="keystore_generating_header">Generating</string>
+    <string name="keystore_entry_alias">Entry alias:</string>
+    <string name="keystore_generate">Generate</string>
+    <string name="keystore_no_alias_error">Must supply an alias</string>
   </resources>
diff --git a/samples/ApiDemos/src/com/example/android/apis/security/KeyStoreUsage.java b/samples/ApiDemos/src/com/example/android/apis/security/KeyStoreUsage.java
new file mode 100644
index 000000000..901806ac5
--- /dev/null
+++ b/samples/ApiDemos/src/com/example/android/apis/security/KeyStoreUsage.java
@@ -0,0 +1,526 @@
+/*
+ * Copyright 2013 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.apis.security;
+
+import com.example.android.apis.R;
+
+import android.app.Activity;
+import android.content.Context;
+import android.database.DataSetObserver;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.security.KeyPairGeneratorSpec;
+import android.util.Base64;
+import android.util.Log;
+import android.view.View;
+import android.view.View.OnClickListener;
+import android.view.View.OnFocusChangeListener;
+import android.view.ViewGroup;
+import android.widget.AdapterView;
+import android.widget.AdapterView.OnItemClickListener;
+import android.widget.AdapterView.OnItemSelectedListener;
+import android.widget.ArrayAdapter;
+import android.widget.Button;
+import android.widget.EditText;
+import android.widget.ListAdapter;
+import android.widget.ListView;
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.KeyStore;
+import java.security.KeyStore.PrivateKeyEntry;
+import java.security.KeyStoreException;
+import java.security.NoSuchAlgorithmException;
+import java.security.NoSuchProviderException;
+import java.security.Signature;
+import java.security.SignatureException;
+import java.security.UnrecoverableEntryException;
+import java.security.cert.CertificateException;
+import java.util.ArrayList;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.Enumeration;
+import java.util.List;
+
+import javax.security.auth.x500.X500Principal;
+
+public class KeyStoreUsage extends Activity {
+    private static final String TAG = "AndroidKeyStoreUsage";
+
+    /**
+     * An instance of {@link java.security.KeyStore} through which this app
+     * talks to the {@code AndroidKeyStore}.
+     */
+    KeyStore mKeyStore;
+
+    /**
+     * Used by the {@code ListView} in our layout to list the keys available in
+     * our {@code KeyStore} by their alias names.
+     */
+    AliasAdapter mAdapter;
+
+    /**
+     * Button in the UI that causes a new keypair to be generated in the
+     * {@code KeyStore}.
+     */
+    Button mGenerateButton;
+
+    /**
+     * Button in the UI that causes data to be signed by a key we selected from
+     * the list available in the {@code KeyStore}.
+     */
+    Button mSignButton;
+
+    /**
+     * Button in the UI that causes data to be signed by a key we selected from
+     * the list available in the {@code KeyStore}.
+     */
+    Button mVerifyButton;
+
+    /**
+     * Button in the UI that causes a key entry to be deleted from the
+     * {@code KeyStore}.
+     */
+    Button mDeleteButton;
+
+    /**
+     * Text field in the UI that holds plaintext.
+     */
+    EditText mPlainText;
+
+    /**
+     * Text field in the UI that holds the signature.
+     */
+    EditText mCipherText;
+
+    /**
+     * The alias of the selected entry in the KeyStore.
+     */
+    private String mSelectedAlias;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        setContentView(R.layout.keystore_usage);
+
+        /*
+         * Set up our {@code ListView} with an adapter that allows
+         * us to choose from the available entry aliases.
+         */
+        ListView lv = (ListView) findViewById(R.id.entries_list);
+        mAdapter = new AliasAdapter(getApplicationContext());
+        lv.setAdapter(mAdapter);
+        lv.setOnItemClickListener(new OnItemClickListener() {
+            @Override
+            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
+                mSelectedAlias = mAdapter.getItem(position);
+                setKeyActionButtonsEnabled(true);
+            }
+        });
+
+        // This is alias the user wants for a generated key.
+        final EditText aliasInput = (EditText) findViewById(R.id.entry_name);
+        mGenerateButton = (Button) findViewById(R.id.generate_button);
+        mGenerateButton.setOnClickListener(new OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                /*
+                 * When the user presses the "Generate" button, we'll
+                 * check the alias isn't blank here.
+                 */
+                final String alias = aliasInput.getText().toString();
+                if (alias == null || alias.length() == 0) {
+                    aliasInput.setError(getResources().getText(R.string.keystore_no_alias_error));
+                } else {
+                    /*
+                     * It's not blank, so disable the generate button while
+                     * the generation of the key is happening. It will be
+                     * enabled by the {@code AsyncTask} later after its
+                     * work is done.
+                     */
+                    aliasInput.setError(null);
+                    mGenerateButton.setEnabled(false);
+                    new GenerateTask().execute(alias);
+                }
+            }
+        });
+
+        mSignButton = (Button) findViewById(R.id.sign_button);
+        mSignButton.setOnClickListener(new OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                final String alias = mSelectedAlias;
+                final String data = mPlainText.getText().toString();
+                if (alias != null) {
+                    setKeyActionButtonsEnabled(false);
+                    new SignTask().execute(alias, data);
+                }
+            }
+        });
+
+        mVerifyButton = (Button) findViewById(R.id.verify_button);
+        mVerifyButton.setOnClickListener(new OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                final String alias = mSelectedAlias;
+                final String data = mPlainText.getText().toString();
+                final String signature = mCipherText.getText().toString();
+                if (alias != null) {
+                    setKeyActionButtonsEnabled(false);
+                    new VerifyTask().execute(alias, data, signature);
+                }
+            }
+        });
+
+        mDeleteButton = (Button) findViewById(R.id.delete_button);
+        mDeleteButton.setOnClickListener(new OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                final String alias = mSelectedAlias;
+                if (alias != null) {
+                    setKeyActionButtonsEnabled(false);
+                    new DeleteTask().execute(alias);
+                }
+            }
+        });
+
+        mPlainText = (EditText) findViewById(R.id.plaintext);
+        mPlainText.setOnFocusChangeListener(new OnFocusChangeListener() {
+            @Override
+            public void onFocusChange(View v, boolean hasFocus) {
+                mPlainText.setTextColor(getResources().getColor(android.R.color.primary_text_dark));
+            }
+        });
+
+        mCipherText = (EditText) findViewById(R.id.ciphertext);
+        mCipherText.setOnFocusChangeListener(new OnFocusChangeListener() {
+            @Override
+            public void onFocusChange(View v, boolean hasFocus) {
+                mCipherText
+                        .setTextColor(getResources().getColor(android.R.color.primary_text_dark));
+            }
+        });
+
+        updateKeyList();
+    }
+
+    private class AliasAdapter extends ArrayAdapter<String> {
+        public AliasAdapter(Context context) {
+            // We want users to choose a key, so use the appropriate layout.
+            super(context, android.R.layout.simple_list_item_single_choice);
+        }
+
+        /**
+         * This clears out all previous aliases and replaces it with the
+         * current entries.
+         */
+        public void setAliases(List<String> items) {
+            clear();
+            addAll(items);
+            notifyDataSetChanged();
+        }
+    }
+
+    private void updateKeyList() {
+        setKeyActionButtonsEnabled(false);
+        new UpdateKeyListTask().execute();
+    }
+
+    /**
+     * Sets all the buttons related to actions that act on an existing key to
+     * enabled or disabled.
+     */
+    private void setKeyActionButtonsEnabled(boolean enabled) {
+        mSignButton.setEnabled(enabled);
+        mVerifyButton.setEnabled(enabled);
+        mDeleteButton.setEnabled(enabled);
+    }
+
+    private class UpdateKeyListTask extends AsyncTask<Void, Void, Enumeration<String>> {
+        @Override
+        protected Enumeration<String> doInBackground(Void... params) {
+            try {
+// BEGIN_INCLUDE(list)
+                /*
+                 * Load the Android KeyStore instance using the the
+                 * "AndroidKeyStore" provider to list out what entries are
+                 * currently stored.
+                 */
+                KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
+                ks.load(null);
+                Enumeration<String> aliases = ks.aliases();
+// END_INCLUDE(list)
+                return aliases;
+            } catch (KeyStoreException e) {
+                Log.w(TAG, "Could not list keys", e);
+                return null;
+            } catch (NoSuchAlgorithmException e) {
+                Log.w(TAG, "Could not list keys", e);
+                return null;
+            } catch (CertificateException e) {
+                Log.w(TAG, "Could not list keys", e);
+                return null;
+            } catch (IOException e) {
+                Log.w(TAG, "Could not list keys", e);
+                return null;
+            }
+        }
+
+        @Override
+        protected void onPostExecute(Enumeration<String> result) {
+            List<String> aliases = new ArrayList<String>();
+            while (result.hasMoreElements()) {
+                aliases.add(result.nextElement());
+            }
+            mAdapter.setAliases(aliases);
+        }
+    }
+
+    private class GenerateTask extends AsyncTask<String, Void, Boolean> {
+        @Override
+        protected Boolean doInBackground(String... params) {
+            final String alias = params[0];
+            try {
+// BEGIN_INCLUDE(generate)
+                /*
+                 * Generate a new entry in the KeyStore by using the
+                 * KeyPairGenerator API. We have to specify the attributes for a
+                 * self-signed X.509 certificate here so the KeyStore can attach
+                 * the public key part to it. It can be replaced later with a
+                 * certificate signed by a Certificate Authority (CA) if needed.
+                 */
+                Calendar cal = Calendar.getInstance();
+                Date now = cal.getTime();
+                cal.add(Calendar.YEAR, 1);
+                Date end = cal.getTime();
+
+                KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
+                kpg.initialize(new KeyPairGeneratorSpec.Builder(getApplicationContext())
+                        .setAlias(alias)
+                        .setStartDate(now)
+                        .setEndDate(end)
+                        .setSerialNumber(BigInteger.valueOf(1))
+                        .setSubject(new X500Principal("CN=test1"))
+                        .build());
+
+                KeyPair kp = kpg.generateKeyPair();
+// END_INCLUDE(generate)
+                return true;
+            } catch (NoSuchAlgorithmException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (InvalidAlgorithmParameterException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (NoSuchProviderException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            }
+        }
+
+        @Override
+        protected void onPostExecute(Boolean result) {
+            updateKeyList();
+            mGenerateButton.setEnabled(true);
+        }
+
+        @Override
+        protected void onCancelled() {
+            mGenerateButton.setEnabled(true);
+        }
+    }
+
+    private class SignTask extends AsyncTask<String, Void, String> {
+        @Override
+        protected String doInBackground(String... params) {
+            final String alias = params[0];
+            final String dataString = params[1];
+            try {
+                byte[] data = dataString.getBytes();
+// BEGIN_INCLUDE(sign)
+                /*
+                 * Use a PrivateKey in the KeyStore to create a signature over
+                 * some data.
+                 */
+                KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
+                ks.load(null);
+                KeyStore.Entry entry = ks.getEntry(alias, null);
+                if (!(entry instanceof PrivateKeyEntry)) {
+                    Log.w(TAG, "Not an instance of a PrivateKeyEntry");
+                    return null;
+                }
+                Signature s = Signature.getInstance("SHA256withRSA");
+                s.initSign(((PrivateKeyEntry) entry).getPrivateKey());
+                s.update(data);
+                byte[] signature = s.sign();
+// END_INCLUDE(sign)
+                return Base64.encodeToString(signature, Base64.DEFAULT);
+            } catch (NoSuchAlgorithmException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (KeyStoreException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (CertificateException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (IOException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (UnrecoverableEntryException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (InvalidKeyException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            } catch (SignatureException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return null;
+            }
+        }
+
+        @Override
+        protected void onPostExecute(String result) {
+            mCipherText.setText(result);
+            setKeyActionButtonsEnabled(true);
+        }
+
+        @Override
+        protected void onCancelled() {
+            mCipherText.setText("error!");
+            setKeyActionButtonsEnabled(true);
+        }
+    }
+
+    private class VerifyTask extends AsyncTask<String, Void, Boolean> {
+        @Override
+        protected Boolean doInBackground(String... params) {
+            final String alias = params[0];
+            final String dataString = params[1];
+            final String signatureString = params[2];
+            try {
+                byte[] data = dataString.getBytes();
+                byte[] signature;
+                try {
+                    signature = Base64.decode(signatureString, Base64.DEFAULT);
+                } catch (IllegalArgumentException e) {
+                    signature = new byte[0];
+                }
+// BEGIN_INCLUDE(verify)
+                /*
+                 * Verify a signature previously made by a PrivateKey in our
+                 * KeyStore. This uses the X.509 certificate attached to our
+                 * private key in the KeyStore to validate a previously
+                 * generated signature.
+                 */
+                KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
+                ks.load(null);
+                KeyStore.Entry entry = ks.getEntry(alias, null);
+                if (!(entry instanceof PrivateKeyEntry)) {
+                    Log.w(TAG, "Not an instance of a PrivateKeyEntry");
+                    return false;
+                }
+                Signature s = Signature.getInstance("SHA256withRSA");
+                s.initVerify(((PrivateKeyEntry) entry).getCertificate());
+                s.update(data);
+                boolean valid = s.verify(signature);
+// END_INCLUDE(verify)
+                return valid;
+            } catch (NoSuchAlgorithmException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (KeyStoreException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (CertificateException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (IOException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (UnrecoverableEntryException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (InvalidKeyException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            } catch (SignatureException e) {
+                Log.w(TAG, "Could not generate key", e);
+                return false;
+            }
+        }
+
+        @Override
+        protected void onPostExecute(Boolean result) {
+            if (result) {
+                mCipherText.setTextColor(getResources().getColor(R.color.solid_green));
+            } else {
+                mCipherText.setTextColor(getResources().getColor(R.color.solid_red));
+            }
+            setKeyActionButtonsEnabled(true);
+        }
+
+        @Override
+        protected void onCancelled() {
+            mCipherText.setText("error!");
+            setKeyActionButtonsEnabled(true);
+            mCipherText.setTextColor(getResources().getColor(android.R.color.primary_text_dark));
+        }
+    }
+
+    private class DeleteTask extends AsyncTask<String, Void, Void> {
+        @Override
+        protected Void doInBackground(String... params) {
+            final String alias = params[0];
+            try {
+// BEGIN_INCLUDE(delete)
+                /*
+                 * Deletes a previously generated or stored entry in the
+                 * KeyStore.
+                 */
+                KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
+                ks.load(null);
+                ks.deleteEntry(alias);
+// END_INCLUDE(delete)
+            } catch (NoSuchAlgorithmException e) {
+                Log.w(TAG, "Could not generate key", e);
+            } catch (KeyStoreException e) {
+                Log.w(TAG, "Could not generate key", e);
+            } catch (CertificateException e) {
+                Log.w(TAG, "Could not generate key", e);
+            } catch (IOException e) {
+                Log.w(TAG, "Could not generate key", e);
+            }
+            return null;
+        }
+
+        @Override
+        protected void onPostExecute(Void result) {
+            updateKeyList();
+        }
+
+        @Override
+        protected void onCancelled() {
+            updateKeyList();
+        }
+    }
+}