First version of project

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/
+.DS_Store
+/build
+*/build
+/captures
+.externalNativeBuild

app/build.gradle

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+apply plugin: 'com.android.application'
+
+android {
+    compileSdkVersion 25
+    buildToolsVersion "25.0.2"
+    defaultConfig {
+        applicationId "ga.uabart.xkate"
+        minSdkVersion 15
+        targetSdkVersion 25
+        versionCode 1
+        versionName "0.0.1"
+    }
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+}
+
+dependencies {
+    compile fileTree(dir: 'libs', include: ['*.jar'])
+    provided 'de.robv.android.xposed:api:53'
+    provided 'de.robv.android.xposed:api:53:sources'
+}

app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in /home/uabart/Android/Sdk/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the proguardFiles
+# directive in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# Add any project specific keep options here:
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}

app/src/main/AndroidManifest.xml

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+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+          package="ga.uabart.xkate">
+
+    <application
+        android:allowBackup="true"
+        android:label="xcate"
+        android:supportsRtl="true">
+
+        <meta-data
+            android:name="xposedmodule"
+            android:value="true" />
+        <meta-data
+            android:name="xposeddescription"
+            android:value="Some encryption hacks for Kate Mobile" />
+        <meta-data
+            android:name="xposedminversion"
+            android:value="48" />
+
+    </application>
+
+</manifest>

app/src/main/assets/xposed_init

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+ga.uabart.xkate.XModule

app/src/main/java/ga/uabart/xkate/TextCipher.java

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+package ga.uabart.xkate;
+
+import java.security.spec.KeySpec;
+
+import javax.crypto.Cipher;
+import javax.crypto.SecretKey;
+import javax.crypto.SecretKeyFactory;
+import javax.crypto.spec.IvParameterSpec;
+import javax.crypto.spec.PBEKeySpec;
+import javax.crypto.spec.SecretKeySpec;
+
+class TextCipher {
+    private static int iterationCount = 1024;
+    private static byte[] iv = "XKateCustomC0de1".getBytes();
+    private static int keyStrength = 256;
+    private static byte[] salt = "RandomSaltXKate".getBytes();
+    private static final String UTF_LOCK = "\uD83D\uDD12\n";
+    private static final String UTF_UNLOCK = "\uD83D\uDD13 ";
+
+    private TextCipher() {
+        throw new IllegalAccessError("Utility class");
+    }
+
+    static String decrypt(String data, String passPhrase) {
+        try {
+            if (data.startsWith(UTF_LOCK)) {
+                String encrypted = data.substring(5);
+                SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
+                KeySpec spec = new PBEKeySpec(passPhrase.toCharArray(), salt, iterationCount, keyStrength);
+                SecretKey tmp = factory.generateSecret(spec);
+                SecretKey key = new SecretKeySpec(tmp.getEncoded(), "AES");
+                Cipher cipher = Cipher.getInstance("AES/CFB/ISO10126Padding");
+                iv[7] = jBaseZ85.decode(data.substring(3, 5))[0];
+                cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
+                byte[] decryptedData = jBaseZ85.decode(encrypted);
+                byte[] utf8 = cipher.doFinal(decryptedData);
+                return UTF_UNLOCK + new String(utf8, "UTF8");
+            } else {
+                return data;
+            }
+        } catch (Exception ignored) {
+            return null;
+        }
+    }
+
+    static String encrypt(String data, String passPhrase) {
+        try {
+            SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
+            KeySpec spec = new PBEKeySpec(passPhrase.toCharArray(), salt, iterationCount, keyStrength);
+            SecretKey tmp = factory.generateSecret(spec);
+            SecretKey key = new SecretKeySpec(tmp.getEncoded(), "AES");
+            Cipher cipher = Cipher.getInstance("AES/CFB/ISO10126Padding");
+            byte[] code = new byte[1];
+            code[0] = (byte) (Math.random() * 255);
+            iv[7] = code[0];
+            cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(iv));
+            byte[] utf8EncryptedData = cipher.doFinal(data.getBytes());
+            return UTF_LOCK + jBaseZ85.encode(code) + jBaseZ85.encode(utf8EncryptedData);
+        } catch (Exception ignored) {
+            return null;
+        }
+    }
+}

app/src/main/java/ga/uabart/xkate/XModule.java

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+package ga.uabart.xkate;
+
+import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
+import android.content.SharedPreferences;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.EditText;
+
+import de.robv.android.xposed.IXposedHookInitPackageResources;
+import de.robv.android.xposed.IXposedHookLoadPackage;
+import de.robv.android.xposed.IXposedHookZygoteInit;
+import de.robv.android.xposed.XC_MethodHook;
+import de.robv.android.xposed.XC_MethodReplacement;
+import de.robv.android.xposed.XposedBridge;
+import de.robv.android.xposed.XposedHelpers;
+import de.robv.android.xposed.callbacks.XC_InitPackageResources;
+import de.robv.android.xposed.callbacks.XC_LoadPackage;
+
+import static android.content.Context.MODE_PRIVATE;
+
+
+public class XModule implements IXposedHookInitPackageResources, IXposedHookLoadPackage, IXposedHookZygoteInit {
+
+    private Activity activity = null;
+    private long chatId;
+    private long groupId;
+    private long messageUid;
+
+    private String generateName(long messageUid, long chatId, long groupId) {
+        if (messageUid != 0) {
+            return "U" + messageUid;
+        } else if (chatId != 0) {
+            return "C" + chatId;
+        } else if (groupId != 0) {
+            return "G" + groupId;
+        }
+        return null;
+    }
+
+    private String getPass(String user, Activity activity) {
+        if (user != null) {
+            SharedPreferences prefs = activity.getSharedPreferences("XKate", MODE_PRIVATE);
+            String pass = prefs.getString(user, null);
+            if ("".equals(pass)) {
+                pass = null;
+            }
+            return pass;
+        } else {
+            return null;
+        }
+    }
+
+    private String getPassword(long messageUid, long chatId, long groupId, Activity activity) {
+        return getPass(generateName(messageUid, chatId, groupId), activity);
+    }
+
+    @Override
+    public void handleInitPackageResources(XC_InitPackageResources.InitPackageResourcesParam resparam) throws Throwable {
+        // maybe this will be needed in future
+    }
+
+    @Override
+    public void handleLoadPackage(XC_LoadPackage.LoadPackageParam param) throws Throwable {
+
+        if ("com.perm.kate".equals(param.packageName)) {
+
+            try {
+
+                final Class<?> messageThreadFragmentClass = XposedHelpers.findClass("com.perm.kate.MessageThreadFragment", param.classLoader);
+
+                // Button
+
+                XposedHelpers.findAndHookMethod(messageThreadFragmentClass, "onCreateView",
+                        LayoutInflater.class, ViewGroup.class, Bundle.class, new XC_MethodHook() {
+
+                            @Override
+                            protected void afterHookedMethod(final MethodHookParam param) throws Throwable {
+                                View sendButton = (View) XposedHelpers.getObjectField(param.thisObject, "sendButton");
+                                activity = (Activity) XposedHelpers.callMethod(param.thisObject, "getActivity");
+                                messageUid = XposedHelpers.getLongField(param.thisObject, "message_uid"); // long
+                                chatId = XposedHelpers.getLongField(param.thisObject, "chat_id"); // long
+                                groupId = XposedHelpers.getLongField(param.thisObject, "group_id"); // long
+                                final String userName = generateName(messageUid, chatId, groupId);
+                                sendButton.setOnLongClickListener(new View.OnLongClickListener() {
+                                                                      @Override
+                                                                      public boolean onLongClick(View v) {
+                                                                          showDialogInputKey(userName, activity);
+                                                                          return true;
+                                                                      }
+                                                                  }
+                                );
+
+                            }
+                        });
+
+                // Sender
+
+                XposedHelpers.findAndHookMethod(messageThreadFragmentClass, "sendClicked", new XC_MethodReplacement() {
+                    @Override
+                    protected Object replaceHookedMethod(MethodHookParam param) throws Throwable {
+
+                        EditText etNewMessage = (EditText) XposedHelpers.getObjectField(param.thisObject, "et_new_message"); // EditText
+                        Object attachments = XposedHelpers.getStaticObjectField(messageThreadFragmentClass, "attachments"); // ArrayList<String>
+                        Object attachmentsObjects = XposedHelpers.getStaticObjectField(messageThreadFragmentClass, "attachments_objects"); // ArrayList<Object>
+                        Object queue = XposedHelpers.getObjectField(param.thisObject, "queue"); // MessageSendQueue
+
+                        String password;
+                        password = getPassword(messageUid, chatId, groupId, activity);
+
+                        if (password != null) {
+                            String encryptedMsg = TextCipher.encrypt(etNewMessage.getText().toString(), password);
+                            if (encryptedMsg != null) {
+                                etNewMessage.setText(encryptedMsg);
+                            }
+                        }
+
+                        XposedHelpers.callMethod(queue, "add", etNewMessage.getText().toString(), messageUid,
+                                chatId, attachments, attachmentsObjects, null, groupId);
+
+                        XposedHelpers.callMethod(param.thisObject, "clearNewMessageEditText");
+                        XposedHelpers.callMethod(param.thisObject, "requeryOnUiThread");
+
+                        return null;
+                    }
+                });
+
+                // Receiver
+
+                final Class<?> messageAdapterCoreClass = XposedHelpers.findClass("com.perm.kate.MessageAdapterCore", param.classLoader);
+                final Class<?> userClass = XposedHelpers.findClass("com.perm.kate.api.User", param.classLoader);
+                final Class<?> messageClass = XposedHelpers.findClass("com.perm.kate.api.Message", param.classLoader);
+                final Class<?> userCacheClass = XposedHelpers.findClass("com.perm.utils.UserCache", param.classLoader);
+
+                XposedHelpers.findAndHookMethod(messageAdapterCoreClass, "displayMessage",
+                        userClass, messageClass, userClass, View.class, userCacheClass, new XC_MethodHook() {
+                            @Override
+                            protected void beforeHookedMethod(MethodHookParam param) throws Throwable {
+                                String body = (String) XposedHelpers.getObjectField(param.args[1], "body");
+                                String password;
+                                password = getPassword(messageUid, chatId, groupId, activity);
+                                if (password != null) {
+                                    String decrypted = TextCipher.decrypt(body, password);
+                                    if (decrypted != null){
+                                        body = decrypted;
+                                    }
+                                }
+                                XposedHelpers.setObjectField(param.args[1], "body", body);
+                            }
+                        });
+
+            } catch (Exception e) {
+                XposedBridge.log(e);
+            }
+
+
+        }
+
+    }
+
+    @Override
+    public void initZygote(StartupParam startupParam) throws Throwable {
+        // maybe this will be needed in future
+    }
+
+    private void savePass(String user, String password, Activity activity) {
+        SharedPreferences.Editor editor = activity.getSharedPreferences("XKate", MODE_PRIVATE).edit();
+        editor.putString(user, password);
+        editor.commit();
+
+    }
+
+    private void showDialogInputKey(final String userName, final Activity activity) {
+        final EditText edittext = new EditText(activity);
+        edittext.setText(getPass(userName, activity));
+
+        AlertDialog alertDialog = new AlertDialog.Builder(activity).create();
+        alertDialog.setMessage("Input password");
+        alertDialog.setView(edittext);
+        alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "Save password",
+                new DialogInterface.OnClickListener() {
+                    public void onClick(DialogInterface dialog, int which) {
+
+                        String password = edittext.getText().toString();
+
+                        savePass(userName, password, activity);
+                        dialog.dismiss();
+                    }
+                });
+        alertDialog.show();
+    }
+
+}