Add support for version 2 XML key files.

As discussed in #4317, the next KeePass2 release will ship with
support for a new generation of XML key files which enable
hash integrity checks.

This patch adds support for reading and generating this new format.
By default, KeePass2 now uses the .keyx extension for generated
key files, which was added to KeePassXC's key generation file chooser
filter. We continue to generate hashed binary key files by default,
but the user can explicitly save the file with the new .keyx
extension to generate an XML v2 key file (currently undocumented).

When opening a database, the key file type is still determined
by content negotation, so the file extension has no impact here.

As an additional change, the legacy key file warnings have been
improved slightly to be less confusing and more helpful.

src/cli/Utils.cpp

@@ -132,9 +132,9 @@ namespace Utils
                 return {};
             }
 
-            if (fileKey->type() != FileKey::Hashed) {
-                err << QObject::tr("WARNING: You are using a legacy key file format which may become\n"
-                                   "unsupported in the future.\n\n"
+            if (fileKey->type() != FileKey::KeePass2XMLv2 && fileKey->type() != FileKey::Hashed) {
+                err << QObject::tr("WARNING: You are using an old key file format which KeePassXC may\n"
+                                   "stop supporting in the future.\n\n"
                                    "Please consider generating a new key file.")
                     << endl;
             }

src/gui/DatabaseOpenWidget.cpp

@@ -301,12 +301,14 @@ QSharedPointer<CompositeKey> DatabaseOpenWidget::buildDatabaseKey()
             m_ui->messageWidget->showMessage(tr("Failed to open key file: %1").arg(errorMsg), MessageWidget::Error);
             return {};
         }
-        if (key->type() != FileKey::Hashed && !config()->get(Config::Messages_NoLegacyKeyFileWarning).toBool()) {
+        if (key->type() != FileKey::KeePass2XMLv2 && key->type() != FileKey::Hashed
+            && !config()->get(Config::Messages_NoLegacyKeyFileWarning).toBool()) {
             QMessageBox legacyWarning;
-            legacyWarning.setWindowTitle(tr("Legacy key file format"));
-            legacyWarning.setText(tr("You are using a legacy key file format which may become\n"
-                                     "unsupported in the future.\n\n"
-                                     "Please consider generating a new key file."));
+            legacyWarning.setWindowTitle(tr("Old key file format"));
+            legacyWarning.setText(tr("You are using an old key file format which KeePassXC may<br>"
+                                     "stop supporting in the future.<br><br>"
+                                     "Please consider generating a new key file by going to:<br>"
+                                     "<strong>Database / Database Security / Change Key File.</strong><br>"));
             legacyWarning.setIcon(QMessageBox::Icon::Warning);
             legacyWarning.addButton(QMessageBox::Ok);
             legacyWarning.setDefaultButton(QMessageBox::Ok);
@@ -355,7 +357,7 @@ void DatabaseOpenWidget::reject()
 
 void DatabaseOpenWidget::browseKeyFile()
 {
-    QString filters = QString("%1 (*);;%2 (*.key)").arg(tr("All files"), tr("Key files"));
+    QString filters = QString("%1 (*);;%2 (*.keyx; *.key)").arg(tr("All files"), tr("Key files"));
     if (!config()->get(Config::RememberLastKeyFiles).toBool()) {
         fileDialog()->setNextForgetDialog();
     }

src/gui/databasekey/KeyFileEditWidget.cpp

@@ -47,12 +47,12 @@ bool KeyFileEditWidget::addToCompositeKey(QSharedPointer<CompositeKey> key)
         return false;
     }
 
-    if (fileKey->type() != FileKey::Hashed) {
+    if (fileKey->type() != FileKey::KeePass2XMLv2 && fileKey->type() != FileKey::Hashed) {
         QMessageBox::warning(getMainWindow(),
-                             tr("Legacy key file format"),
-                             tr("You are using a legacy key file format which may become\n"
-                                "unsupported in the future.\n\n"
-                                "Generate a new key file in the database security settings."),
+                             tr("Old key file format"),
+                             tr("You selected a key file in an old format which KeePassXC<br>"
+                                "may stop supporting in the future.<br><br>"
+                                "Please consider generating a new key file instead."),
                              QMessageBox::Ok);
     }
 
@@ -96,7 +96,7 @@ void KeyFileEditWidget::createKeyFile()
     if (!m_compEditWidget) {
         return;
     }
-    QString filters = QString("%1 (*.key);;%2 (*)").arg(tr("Key files"), tr("All files"));
+    QString filters = QString("%1 (*.keyx; *.key);;%2 (*)").arg(tr("Key files"), tr("All files"));
     QString fileName = fileDialog()->getSaveFileName(this, tr("Create Key File..."), QString(), filters);
 
     if (!fileName.isEmpty()) {
@@ -119,7 +119,7 @@ void KeyFileEditWidget::browseKeyFile()
     if (!m_compEditWidget) {
         return;
     }
-    QString filters = QString("%1 (*.key);;%2 (*)").arg(tr("Key files"), tr("All files"));
+    QString filters = QString("%1 (*.keyx; *.key);;%2 (*)").arg(tr("Key files"), tr("All files"));
     QString fileName = fileDialog()->getOpenFileName(this, tr("Select a key file"), QString(), filters);
 
     if (QFileInfo(fileName).canonicalFilePath() == m_parent->getDatabase()->canonicalFilePath()) {