Refactoring password encryption (#147)

.circleci/config.yml

@@ -124,7 +124,7 @@ jobs:
       - *attach_workspace
       - run:
           name: Setup emulator
-          command: sdkmanager "system-images;android-16;default;armeabi-v7a" && echo "no" | avdmanager create avd -n test -k "system-images;android-16;default;armeabi-v7a"
+          command: sdkmanager "system-images;android-19;default;armeabi-v7a" && echo "no" | avdmanager create avd -n test -k "system-images;android-19;default;armeabi-v7a"
       - run:
           name: Launch emulator
           command: export LD_LIBRARY_PATH=${ANDROID_HOME}/emulator/lib64:${ANDROID_HOME}/emulator/lib64/qt/lib && emulator64-arm -avd test -noaudio -no-boot-anim -no-window -accel on
@@ -140,12 +140,9 @@ jobs:
             # unlock the emulator screen
             sleep 30
             adb shell input keyevent 82
-      - run:
-          name: Clean project
-          command: ./gradlew clean --no-daemon --stacktrace --console=plain -PdisablePreDex
       - run:
           name: Run instrumented tests
-          command: ./gradlew createDebugCoverageReport --no-daemon --stacktrace --console=plain -PdisablePreDex
+          command: ./gradlew clean createDebugCoverageReport jacocoTestReport --no-daemon --stacktrace --console=plain -PdisablePreDex
       - run:
           name: Collect logs from emulator
           command: adb logcat -d > ./app/build/reports/logcat_emulator.txt

app/build.gradle

@@ -141,4 +141,5 @@ dependencies {
 
     androidTestImplementation "com.android.support.test:runner:$testRunner"
     androidTestImplementation "org.mockito:mockito-android:$mockito"
+    androidTestImplementation "org.jetbrains.kotlin:kotlin-test:$kotlin_version"
 }

app/src/androidTest/java/io/github/wulkanowy/utils/security/ScramblerTest.java

@@ -1,25 +0,0 @@
-package io.github.wulkanowy.utils.security;
-
-import android.content.Context;
-import android.support.test.InstrumentationRegistry;
-import android.support.test.filters.SdkSuppress;
-import android.support.test.filters.SmallTest;
-import android.support.test.runner.AndroidJUnit4;
-
-import org.junit.Assert;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-
-@SmallTest
-@RunWith(AndroidJUnit4.class)
-public class ScramblerTest {
-
-    @Test
-    @SdkSuppress(minSdkVersion = 18)
-    public void encryptDecryptTest() throws Exception {
-        Context targetContext = InstrumentationRegistry.getTargetContext();
-
-        Assert.assertEquals("PASS", Scrambler.decrypt("TEST",
-                Scrambler.encrypt("TEST", "PASS", targetContext)));
-    }
-}

app/src/androidTest/java/io/github/wulkanowy/utils/security/ScramblerTest.kt

@@ -0,0 +1,48 @@
+package io.github.wulkanowy.utils.security
+
+import android.support.test.InstrumentationRegistry
+import android.support.test.filters.SdkSuppress
+import android.support.test.filters.SmallTest
+import android.support.test.runner.AndroidJUnit4
+import org.junit.Test
+import org.junit.runner.RunWith
+import java.security.KeyStore
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+
+@SmallTest
+@RunWith(AndroidJUnit4::class)
+class ScramblerTest {
+
+    @Test
+    fun encryptDecryptTest() {
+        assertEquals("TEST", Scrambler.decrypt(Scrambler.encrypt("TEST",
+                InstrumentationRegistry.getTargetContext())))
+    }
+
+    @Test
+    fun emptyTextEncryptTest() {
+        assertFailsWith<ScramblerException> {
+            Scrambler.decrypt("")
+        }
+
+        assertFailsWith<ScramblerException> {
+            Scrambler.encrypt("", InstrumentationRegistry.getTargetContext())
+        }
+    }
+
+    @Test
+    @SdkSuppress(minSdkVersion = 18)
+    fun emptyKeyStoreTest() {
+        val text = Scrambler.encrypt("test", InstrumentationRegistry.getTargetContext())
+
+        val keyStore = KeyStore.getInstance("AndroidKeyStore")
+        keyStore.load(null)
+        keyStore.deleteEntry("USER_PASSWORD")
+
+        assertFailsWith<ScramblerException> {
+            Scrambler.decrypt(text)
+        }
+    }
+}

app/src/main/AndroidManifest.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="io.github.wulkanowy"
-
     android:installLocation="internalOnly">
 
     <uses-permission android:name="android.permission.INTERNET" />
@@ -36,8 +35,7 @@
             android:name=".ui.main.MainActivity"
             android:configChanges="orientation|screenSize"
             android:label="@string/activity_dashboard_text"
-            android:launchMode="singleTop"
-            />
+            android:launchMode="singleTop" />
         <activity
             android:name="com.google.android.gms.oss.licenses.OssLicensesMenuActivity"
             android:theme="@style/WulkanowyTheme.DarkActionBar" />

app/src/main/java/io/github/wulkanowy/WulkanowyApp.java

@@ -1,74 +0,0 @@
-package io.github.wulkanowy;
-
-import com.crashlytics.android.Crashlytics;
-import com.crashlytics.android.answers.Answers;
-import com.crashlytics.android.core.CrashlyticsCore;
-import com.jakewharton.threetenabp.AndroidThreeTen;
-
-import org.greenrobot.greendao.query.QueryBuilder;
-
-import javax.inject.Inject;
-
-import dagger.android.AndroidInjector;
-import dagger.android.support.DaggerApplication;
-import eu.davidea.flexibleadapter.FlexibleAdapter;
-import io.fabric.sdk.android.Fabric;
-import io.github.wulkanowy.data.RepositoryContract;
-import io.github.wulkanowy.di.DaggerAppComponent;
-import io.github.wulkanowy.utils.FabricUtils;
-import io.github.wulkanowy.utils.LoggerUtils;
-import timber.log.Timber;
-
-public class WulkanowyApp extends DaggerApplication {
-
-    @Inject
-    RepositoryContract repository;
-
-    @Override
-    public void onCreate() {
-        super.onCreate();
-        AndroidThreeTen.init(this);
-
-        if (BuildConfig.DEBUG) {
-            enableDebugLog();
-        }
-        initializeFabric();
-        initializeUserSession();
-    }
-
-    private void initializeUserSession() {
-        if (repository.getSharedRepo().isUserLoggedIn()) {
-            try {
-                repository.getSyncRepo().initLastUser();
-                FabricUtils.logLogin("Open app", true);
-            } catch (Exception e) {
-                FabricUtils.logLogin("Open app", false);
-                Timber.e(e, "An error occurred when the application was started");
-            }
-        }
-    }
-
-    private void enableDebugLog() {
-        QueryBuilder.LOG_VALUES = true;
-        FlexibleAdapter.enableLogs(eu.davidea.flexibleadapter.utils.Log.Level.DEBUG);
-        Timber.plant(new LoggerUtils.DebugLogTree());
-    }
-
-    private void initializeFabric() {
-        Fabric.with(new Fabric.Builder(this)
-                .kits(
-                        new Crashlytics.Builder()
-                                .core(new CrashlyticsCore.Builder().disabled(BuildConfig.DEBUG).build())
-                                .build(),
-                        new Answers()
-                )
-                .debuggable(BuildConfig.DEBUG)
-                .build());
-        Timber.plant(new LoggerUtils.CrashlyticsTree());
-    }
-
-    @Override
-    protected AndroidInjector<? extends DaggerApplication> applicationInjector() {
-        return DaggerAppComponent.builder().create(this);
-    }
-}

app/src/main/java/io/github/wulkanowy/WulkanowyApp.kt

@@ -0,0 +1,74 @@
+package io.github.wulkanowy
+
+import com.crashlytics.android.Crashlytics
+import com.crashlytics.android.answers.Answers
+import com.crashlytics.android.core.CrashlyticsCore
+import com.jakewharton.threetenabp.AndroidThreeTen
+import dagger.android.AndroidInjector
+import dagger.android.support.DaggerApplication
+import eu.davidea.flexibleadapter.FlexibleAdapter
+import io.fabric.sdk.android.Fabric
+import io.github.wulkanowy.data.RepositoryContract
+import io.github.wulkanowy.di.DaggerAppComponent
+import io.github.wulkanowy.utils.FabricUtils
+import io.github.wulkanowy.utils.LoggerUtils
+import io.github.wulkanowy.utils.security.ScramblerException
+import org.greenrobot.greendao.query.QueryBuilder
+import timber.log.Timber
+import javax.inject.Inject
+
+class WulkanowyApp : DaggerApplication() {
+
+    @Inject
+    internal lateinit var repository: RepositoryContract
+
+    override fun onCreate() {
+        super.onCreate()
+        AndroidThreeTen.init(this)
+
+        if (BuildConfig.DEBUG) {
+            enableDebugLog()
+        }
+        initializeFabric()
+        initializeUserSession()
+    }
+
+    private fun initializeUserSession() {
+        if (repository.sharedRepo.isUserLoggedIn) {
+            try {
+                repository.syncRepo.initLastUser()
+                FabricUtils.logLogin("Open app", true)
+            } catch (e: Exception) {
+                FabricUtils.logLogin("Open app", false)
+                Timber.e(e, "An error occurred when the application was started")
+            } catch (e: ScramblerException) {
+                FabricUtils.logLogin("Open app", false)
+                Timber.e(e, "A security error has occurred")
+                repository.cleanAllData()
+            }
+
+        }
+    }
+
+    private fun enableDebugLog() {
+        QueryBuilder.LOG_VALUES = true
+        FlexibleAdapter.enableLogs(eu.davidea.flexibleadapter.utils.Log.Level.DEBUG)
+        Timber.plant(LoggerUtils.DebugLogTree())
+    }
+
+    private fun initializeFabric() {
+        Fabric.with(Fabric.Builder(this)
+                .kits(
+                        Crashlytics.Builder()
+                                .core(CrashlyticsCore.Builder().disabled(BuildConfig.DEBUG).build())
+                                .build(),
+                        Answers()
+                )
+                .debuggable(BuildConfig.DEBUG)
+                .build())
+        Timber.plant(LoggerUtils.CrashlyticsTree())
+    }
+
+    override fun applicationInjector(): AndroidInjector<out DaggerApplication> =
+            DaggerAppComponent.builder().create(this)
+}

app/src/main/java/io/github/wulkanowy/data/db/dao/migrations/Migration23.java

@@ -30,7 +30,7 @@ public class Migration23 implements DbHelper.Migration {
         final Map<String, String> user = getAccountData(db);
         vulcan.setCredentials(
                 user.get("email"),
-                Scrambler.decrypt(user.get("email"), user.get("password")),
+                Scrambler.decrypt(user.get("password")),
                 user.get("symbol"),
                 user.get("school_id"),
                 "", // inserted in code bellow

app/src/main/java/io/github/wulkanowy/data/db/resources/ResourcesRepository.java

@@ -14,7 +14,6 @@ import io.github.wulkanowy.R;
 import io.github.wulkanowy.api.NotLoggedInErrorException;
 import io.github.wulkanowy.data.db.dao.entities.AttendanceLesson;
 import io.github.wulkanowy.utils.AppConstant;
-import io.github.wulkanowy.utils.security.CryptoException;
 import timber.log.Timber;
 
 @Singleton
@@ -39,11 +38,9 @@ public class ResourcesRepository implements ResourcesContract {
 
     @Override
     public String getErrorLoginMessage(Exception exception) {
-        Timber.e(exception,"%s encountered a error", AppConstant.APP_NAME);
+        Timber.e(exception, "%s encountered a error", AppConstant.APP_NAME);
 
-        if (exception instanceof CryptoException) {
-            return resources.getString(R.string.encrypt_failed_text);
-        } else if (exception instanceof UnknownHostException) {
+        if (exception instanceof UnknownHostException) {
             return resources.getString(R.string.noInternet_text);
         } else if (exception instanceof SocketTimeoutException) {
             return resources.getString(R.string.generic_timeout_error);

app/src/main/java/io/github/wulkanowy/data/sync/AccountSync.java

@@ -26,8 +26,8 @@ import io.github.wulkanowy.data.db.dao.entities.Symbol;
 import io.github.wulkanowy.data.db.dao.entities.SymbolDao;
 import io.github.wulkanowy.data.db.shared.SharedPrefContract;
 import io.github.wulkanowy.utils.DataObjectConverter;
-import io.github.wulkanowy.utils.security.CryptoException;
 import io.github.wulkanowy.utils.security.Scrambler;
+import io.github.wulkanowy.utils.security.ScramblerException;
 import timber.log.Timber;
 
 @Singleton
@@ -51,7 +51,7 @@ public class AccountSync {
     }
 
     public void registerUser(String email, String password, String symbol)
-            throws VulcanException, IOException, CryptoException {
+            throws VulcanException, IOException, ScramblerException {
 
         clearUserData();
 
@@ -79,11 +79,11 @@ public class AccountSync {
         Timber.i("Register end");
     }
 
-    private Account insertAccount(String email, String password) throws CryptoException {
+    private Account insertAccount(String email, String password) throws ScramblerException {
         Timber.d("Register account");
         Account account = new Account()
                 .setEmail(email)
-                .setPassword(Scrambler.encrypt(email, password, context));
+                .setPassword(Scrambler.encrypt(password, context));
         daoSession.getAccountDao().insert(account);
         return account;
     }
@@ -150,7 +150,7 @@ public class AccountSync {
         daoSession.getSemesterDao().insertInTx(semesterList);
     }
 
-    public void initLastUser() throws CryptoException {
+    public void initLastUser() throws ScramblerException {
 
         long userId = sharedPref.getCurrentUserId();
 
@@ -180,7 +180,7 @@ public class AccountSync {
 
         vulcan.setCredentials(
                 account.getEmail(),
-                Scrambler.decrypt(account.getEmail(), account.getPassword()),
+                Scrambler.decrypt(account.getPassword()),
                 symbol.getSymbol(),
                 school.getRealId(),
                 student.getRealId(),

app/src/main/java/io/github/wulkanowy/data/sync/SyncContract.java

@@ -6,15 +6,16 @@ import java.text.ParseException;
 import javax.inject.Singleton;
 
 import io.github.wulkanowy.api.VulcanException;
-import io.github.wulkanowy.utils.security.CryptoException;
+import io.github.wulkanowy.utils.security.ScramblerException;
 
 @Singleton
 public interface SyncContract {
 
     void registerUser(String email, String password, String symbol) throws VulcanException,
-            IOException, CryptoException;
+            IOException, ScramblerException;
+
+    void initLastUser() throws IOException, ScramblerException;
 
-    void initLastUser() throws IOException, CryptoException;
 
     void syncGrades(int semesterName) throws VulcanException, IOException, ParseException;
 

app/src/main/java/io/github/wulkanowy/data/sync/SyncRepository.java

@@ -7,7 +7,7 @@ import javax.inject.Singleton;
 
 import io.github.wulkanowy.api.VulcanException;
 import io.github.wulkanowy.data.db.dao.DbContract;
-import io.github.wulkanowy.utils.security.CryptoException;
+import io.github.wulkanowy.utils.security.ScramblerException;
 
 @Singleton
 public class SyncRepository implements SyncContract {
@@ -41,12 +41,12 @@ public class SyncRepository implements SyncContract {
 
     @Override
     public void registerUser(String email, String password, String symbol) throws VulcanException,
-            IOException, CryptoException {
+            IOException, ScramblerException {
         accountSync.registerUser(email, password, symbol);
     }
 
     @Override
-    public void initLastUser() throws CryptoException {
+    public void initLastUser() throws ScramblerException {
         accountSync.initLastUser();
     }
 

app/src/main/java/io/github/wulkanowy/utils/security/CryptoException.java

@@ -1,9 +0,0 @@
-package io.github.wulkanowy.utils.security;
-
-
-public class CryptoException extends Exception {
-
-    public CryptoException(String message) {
-        super(message);
-    }
-}

app/src/main/java/io/github/wulkanowy/utils/security/Scrambler.java

@@ -1,176 +0,0 @@
-package io.github.wulkanowy.utils.security;
-
-
-import android.annotation.TargetApi;
-import android.content.Context;
-import android.os.Build;
-import android.security.KeyPairGeneratorSpec;
-import android.security.keystore.KeyGenParameterSpec;
-import android.security.keystore.KeyProperties;
-import android.util.Base64;
-
-import org.apache.commons.lang3.ArrayUtils;
-
-import java.io.ByteArrayInputStream;
-import java.io.ByteArrayOutputStream;
-import java.math.BigInteger;
-import java.security.KeyPairGenerator;
-import java.security.KeyStore;
-import java.security.interfaces.RSAPublicKey;
-import java.security.spec.AlgorithmParameterSpec;
-import java.util.ArrayList;
-import java.util.Calendar;
-
-import javax.crypto.Cipher;
-import javax.crypto.CipherInputStream;
-import javax.crypto.CipherOutputStream;
-import javax.security.auth.x500.X500Principal;
-
-import timber.log.Timber;
-
-public final class Scrambler {
-
-    private static final String ANDROID_KEYSTORE = "AndroidKeyStore";
-
-    private static KeyStore keyStore;
-
-    private Scrambler() {
-        throw new IllegalStateException("Utility class");
-    }
-
-    public static String encrypt(String email, String plainText, Context context)
-            throws CryptoException {
-
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
-            loadKeyStore();
-            generateNewKey(email, context);
-            return encryptString(email, plainText);
-        }
-        return new String(Base64.encode(plainText.getBytes(), Base64.DEFAULT));
-    }
-
-    public static String decrypt(String email, String encryptedText) throws CryptoException {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
-            loadKeyStore();
-            return decryptString(email, encryptedText);
-        }
-        return new String(Base64.decode(encryptedText, Base64.DEFAULT));
-    }
-
-    private static void loadKeyStore() throws CryptoException {
-        try {
-            keyStore = KeyStore.getInstance(ANDROID_KEYSTORE);
-            keyStore.load(null);
-        } catch (Exception e) {
-            throw new CryptoException(e.getMessage());
-        }
-    }
-
-    @SuppressWarnings("deprecation")
-    @TargetApi(18)
-    private static void generateNewKey(String alias, Context context) throws CryptoException {
-
-        Calendar start = Calendar.getInstance();
-        Calendar end = Calendar.getInstance();
-
-        AlgorithmParameterSpec spec;
-
-        end.add(Calendar.YEAR, 10);
-        if (!"".equals(alias)) {
-            try {
-                if (!keyStore.containsAlias(alias)) {
-                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
-                        spec = new KeyGenParameterSpec.Builder(alias,
-                                KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
-                                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
-                                .setDigests(KeyProperties.DIGEST_SHA256)
-                                .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PKCS1)
-                                .setCertificateNotBefore(start.getTime())
-                                .setCertificateNotAfter(end.getTime())
-                                .build();
-
-                    } else {
-                        spec = new KeyPairGeneratorSpec.Builder(context)
-                                .setAlias(alias)
-                                .setSubject(new X500Principal("CN=" + alias))
-                                .setSerialNumber(BigInteger.TEN)
-                                .setStartDate(start.getTime())
-                                .setEndDate(end.getTime())
-                                .build();
-                    }
-
-                    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA",
-                            ANDROID_KEYSTORE);
-                    keyPairGenerator.initialize(spec);
-                    keyPairGenerator.generateKeyPair();
-                }
-            } catch (Exception e) {
-                throw new CryptoException(e.getMessage());
-            }
-        } else {
-            throw new CryptoException("GenerateNewKey - String is empty");
-        }
-
-        Timber.d("Key pair are create");
-
-    }
-
-    private static String encryptString(String alias, String text) throws CryptoException {
-
-        if (!alias.isEmpty() && !text.isEmpty()) {
-            try {
-                KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(alias, null);
-                RSAPublicKey publicKey = (RSAPublicKey) privateKeyEntry.getCertificate().getPublicKey();
-
-                Cipher input = Cipher.getInstance("RSA/ECB/PKCS1Padding");
-                input.init(Cipher.ENCRYPT_MODE, publicKey);
-
-                ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
-                CipherOutputStream cipherOutputStream = new CipherOutputStream(
-                        outputStream, input);
-                cipherOutputStream.write(text.getBytes("UTF-8"));
-                cipherOutputStream.close();
-
-                byte[] values = outputStream.toByteArray();
-
-                return Base64.encodeToString(values, Base64.DEFAULT);
-
-            } catch (Exception e) {
-                throw new CryptoException(e.getMessage());
-            }
-        } else {
-            throw new CryptoException("EncryptString - String is empty");
-        }
-    }
-
-    private static String decryptString(String alias, String text) throws CryptoException {
-
-        if (!alias.isEmpty() && !text.isEmpty()) {
-            try {
-                KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(alias, null);
-
-                Cipher output = Cipher.getInstance("RSA/ECB/PKCS1Padding");
-                output.init(Cipher.DECRYPT_MODE, privateKeyEntry.getPrivateKey());
-
-                CipherInputStream cipherInputStream = new CipherInputStream(
-                        new ByteArrayInputStream(Base64.decode(text, Base64.DEFAULT)), output);
-
-                ArrayList<Byte> values = new ArrayList<>();
-
-                int nextByte;
-
-                while ((nextByte = cipherInputStream.read()) != -1) {
-                    values.add((byte) nextByte);
-                }
-
-                Byte[] bytes = values.toArray(new Byte[values.size()]);
-
-                return new String(ArrayUtils.toPrimitive(bytes), 0, bytes.length, "UTF-8");
-            } catch (Exception e) {
-                throw new CryptoException(e.getMessage());
-            }
-        } else {
-            throw new CryptoException("EncryptString - String is empty");
-        }
-    }
-}

app/src/main/java/io/github/wulkanowy/utils/security/Scrambler.kt

@@ -0,0 +1,172 @@
+@file:Suppress("DEPRECATION")
+
+package io.github.wulkanowy.utils.security
+
+import android.annotation.TargetApi
+import android.content.Context
+import android.os.Build.VERSION.SDK_INT
+import android.os.Build.VERSION_CODES.JELLY_BEAN_MR2
+import android.os.Build.VERSION_CODES.M
+import android.security.KeyPairGeneratorSpec
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties.*
+import android.util.Base64
+import android.util.Base64.DEFAULT
+import org.apache.commons.lang3.StringUtils
+import timber.log.Timber
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+import java.math.BigInteger
+import java.nio.charset.Charset
+import java.security.KeyPairGenerator
+import java.security.KeyStore
+import java.security.PrivateKey
+import java.security.PublicKey
+import java.util.*
+import javax.crypto.Cipher
+import javax.crypto.Cipher.DECRYPT_MODE
+import javax.crypto.Cipher.ENCRYPT_MODE
+import javax.crypto.CipherInputStream
+import javax.crypto.CipherOutputStream
+import javax.security.auth.x500.X500Principal
+import kotlin.collections.ArrayList
+
+object Scrambler {
+
+    private const val KEY_ALIAS = "USER_PASSWORD"
+
+    private const val ALGORITHM_RSA = "RSA"
+
+    private const val KEYSTORE_NAME = "AndroidKeyStore"
+
+    private const val KEY_TRANSFORMATION_ALGORITHM = "RSA/ECB/PKCS1Padding"
+
+    private const val KEY_CIPHER_JELLY_PROVIDER = "AndroidOpenSSL"
+
+    private const val KEY_CIPHER_M_PROVIDER = "AndroidKeyStoreBCWorkaround"
+
+    private val KEY_CHARSET = Charset.forName("UTF-8")
+
+    @JvmStatic
+    fun encrypt(plainText: String, context: Context): String {
+        if (StringUtils.isEmpty(plainText)) {
+            throw ScramblerException("Text to be encrypted is empty")
+        }
+
+        if (SDK_INT < JELLY_BEAN_MR2) {
+            return String(Base64.encode(plainText.toByteArray(KEY_CHARSET), DEFAULT), KEY_CHARSET)
+        }
+
+        try {
+            if (!isKeyPairExist()) {
+                generateKeyPair(context)
+            }
+
+            val cipher = getCipher()
+            cipher.init(ENCRYPT_MODE, getPublicKey())
+
+            val outputStream = ByteArrayOutputStream()
+            val cipherOutputStream = CipherOutputStream(outputStream, cipher)
+            cipherOutputStream.write(plainText.toByteArray(KEY_CHARSET))
+            cipherOutputStream.close()
+
+            return Base64.encodeToString(outputStream.toByteArray(), DEFAULT)
+        } catch (e: Exception) {
+            throw ScramblerException("An error occurred while encrypting text", e)
+        }
+
+    }
+
+    @JvmStatic
+    fun decrypt(cipherText: String): String {
+        if (StringUtils.isEmpty(cipherText)) {
+            throw ScramblerException("Text to be encrypted is empty")
+        }
+
+        if (SDK_INT < JELLY_BEAN_MR2) {
+            return String(Base64.decode(cipherText.toByteArray(KEY_CHARSET), DEFAULT), KEY_CHARSET)
+        }
+
+        if (!isKeyPairExist()) {
+            throw ScramblerException("KeyPair doesn't exist")
+        }
+
+        try {
+            val cipher = getCipher()
+            cipher.init(DECRYPT_MODE, getPrivateKey())
+
+            val input = CipherInputStream(ByteArrayInputStream(Base64.decode(cipherText, DEFAULT)), cipher)
+            val values = ArrayList<Byte>()
+
+            var nextByte = 0
+            while ({ nextByte = input.read(); nextByte }() != -1) {
+                values.add(nextByte.toByte())
+            }
+
+            val bytes = ByteArray(values.size)
+            for (i in bytes.indices) {
+                bytes[i] = values[i]
+            }
+            return String(bytes, 0, bytes.size, KEY_CHARSET)
+        } catch (e: Exception) {
+            throw ScramblerException("An error occurred while decrypting text", e)
+        }
+
+    }
+
+    private fun getKeyStoreInstance(): KeyStore {
+        val keyStore = KeyStore.getInstance(KEYSTORE_NAME)
+        keyStore.load(null)
+        return keyStore
+    }
+
+    private fun getPublicKey(): PublicKey =
+            (getKeyStoreInstance().getEntry(KEY_ALIAS, null) as KeyStore.PrivateKeyEntry)
+                    .certificate.publicKey
+
+
+    private fun getPrivateKey(): PrivateKey =
+            (getKeyStoreInstance().getEntry(KEY_ALIAS, null) as KeyStore.PrivateKeyEntry).privateKey
+
+
+    private fun getCipher(): Cipher {
+        if (SDK_INT >= M) {
+            return Cipher.getInstance(KEY_TRANSFORMATION_ALGORITHM, KEY_CIPHER_M_PROVIDER)
+        }
+
+        return Cipher.getInstance(KEY_TRANSFORMATION_ALGORITHM, KEY_CIPHER_JELLY_PROVIDER)
+    }
+
+    @TargetApi(JELLY_BEAN_MR2)
+    private fun generateKeyPair(context: Context) {
+        val spec = if (SDK_INT >= M) {
+            KeyGenParameterSpec.Builder(KEY_ALIAS, PURPOSE_DECRYPT or PURPOSE_ENCRYPT)
+                    .setDigests(DIGEST_SHA256, DIGEST_SHA512)
+                    .setCertificateSubject(X500Principal("CN=Wulkanowy"))
+                    .setEncryptionPaddings(ENCRYPTION_PADDING_RSA_PKCS1)
+                    .setSignaturePaddings(SIGNATURE_PADDING_RSA_PKCS1)
+                    .setCertificateSerialNumber(BigInteger.TEN)
+                    .build()
+        } else {
+            val start = Calendar.getInstance()
+            val end = Calendar.getInstance()
+            end.add(Calendar.YEAR, 99)
+
+            KeyPairGeneratorSpec.Builder(context)
+                    .setAlias(KEY_ALIAS)
+                    .setSubject(X500Principal("CN=Wulkanowy"))
+                    .setSerialNumber(BigInteger.TEN)
+                    .setStartDate(start.time)
+                    .setEndDate(end.time)
+                    .build()
+        }
+
+        val generator = KeyPairGenerator.getInstance(ALGORITHM_RSA, KEYSTORE_NAME)
+        generator.initialize(spec)
+        generator.generateKeyPair()
+
+        Timber.i("A new KeyPair has been generated")
+    }
+
+    private fun isKeyPairExist(): Boolean = getKeyStoreInstance().getKey(KEY_ALIAS, null) != null
+}

app/src/main/java/io/github/wulkanowy/utils/security/ScramblerException.kt

@@ -0,0 +1,6 @@
+package io.github.wulkanowy.utils.security
+
+class ScramblerException : Exception {
+    constructor(message: String, cause: Throwable) : super(message, cause)
+    constructor(message: String) : super(message)
+}