Use PasswordKey for storing transformed secrets.

The transformed secrets were stored in normal QByteArrays,
which are at risk of being swapped out. We now use secure
PasswordKey objects instead. There are still a few areas
where QByteArrays are used for storing secrets, but since
they are all temporary, they are less critical. It may be
worth hunting those down as well, though.

src/core/Database.h

@@ -23,12 +23,15 @@
 #include <QHash>
 #include <QObject>
 #include <QPointer>
+#include <QScopedPointer>
 
 #include "config-keepassx.h"
 #include "crypto/kdf/AesKdf.h"
 #include "crypto/kdf/Kdf.h"
 #include "format/KeePass2.h"
+#include "keys/PasswordKey.h"
 #include "keys/CompositeKey.h"
+
 class Entry;
 enum class EntryReferenceType;
 class FileWatcher;
@@ -162,18 +165,39 @@ private:
         bool isReadOnly = false;
         QUuid cipher = KeePass2::CIPHER_AES256;
         CompressionAlgorithm compressionAlgorithm = CompressionGZip;
-        QByteArray transformedMasterKey;
-        QSharedPointer<Kdf> kdf = QSharedPointer<AesKdf>::create(true);
-        QSharedPointer<const CompositeKey> key;
+
+        QScopedPointer<PasswordKey> masterSeed;
+        QScopedPointer<PasswordKey> transformedMasterKey;
+        QScopedPointer<PasswordKey> challengeResponseKey;
+
         bool hasKey = false;
-        QByteArray masterSeed;
-        QByteArray challengeResponseKey;
+        QSharedPointer<const CompositeKey> key;
+        QSharedPointer<Kdf> kdf = QSharedPointer<AesKdf>::create(true);
+
         QVariantMap publicCustomData;
 
         DatabaseData()
+            : masterSeed(new PasswordKey())
+            , transformedMasterKey(new PasswordKey())
+            , challengeResponseKey(new PasswordKey())
         {
             kdf->randomizeSeed();
         }
+
+        void clear()
+        {
+            filePath.clear();
+
+            masterSeed.reset();
+            transformedMasterKey.reset();
+            challengeResponseKey.reset();
+
+            hasKey = false;
+            key.reset();
+            kdf.reset();
+
+            publicCustomData.clear();
+        }
     };
 
     void createRecycleBin();