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.cpp

@@ -316,7 +316,11 @@ bool Database::writeDatabase(QIODevice* device, QString* error)
         return false;
     }
 
-    QByteArray oldTransformedKey = m_data.transformedMasterKey;
+    PasswordKey oldTransformedKey;
+    if (m_data.hasKey) {
+        oldTransformedKey.setHash(m_data.transformedMasterKey->rawKey());
+    }
+
     KeePass2Writer writer;
     setEmitModified(false);
     writer.writeDatabase(device, this);
@@ -329,9 +333,10 @@ bool Database::writeDatabase(QIODevice* device, QString* error)
         return false;
     }
 
-    Q_ASSERT(!m_data.transformedMasterKey.isEmpty());
-    Q_ASSERT(m_data.transformedMasterKey != oldTransformedKey);
-    if (m_data.transformedMasterKey.isEmpty() || m_data.transformedMasterKey == oldTransformedKey) {
+    QByteArray newKey = m_data.transformedMasterKey->rawKey();
+    Q_ASSERT(!newKey.isEmpty());
+    Q_ASSERT(newKey != oldTransformedKey.rawKey());
+    if (newKey.isEmpty() || newKey == oldTransformedKey.rawKey()) {
         if (error) {
             *error = tr("Key not transformed. This is a bug, please report it to the developers!");
         }
@@ -382,6 +387,7 @@ bool Database::import(const QString& xmlExportPath, QString* error)
  *
  * A previously reparented root group will not be freed.
  */
+
 void Database::releaseData()
 {
     s_uuidMap.remove(m_uuid);
@@ -391,7 +397,7 @@ void Database::releaseData()
         emit databaseDiscarded();
     }
 
-    m_data = DatabaseData();
+    m_data.clear();
 
     if (m_rootGroup && m_rootGroup->parent() == this) {
         delete m_rootGroup;
@@ -630,19 +636,24 @@ Database::CompressionAlgorithm Database::compressionAlgorithm() const
 
 QByteArray Database::transformedMasterKey() const
 {
-    return m_data.transformedMasterKey;
+    return m_data.transformedMasterKey->rawKey();
 }
 
 QByteArray Database::challengeResponseKey() const
 {
-    return m_data.challengeResponseKey;
+    return m_data.challengeResponseKey->rawKey();
 }
 
 bool Database::challengeMasterSeed(const QByteArray& masterSeed)
 {
     if (m_data.key) {
-        m_data.masterSeed = masterSeed;
-        return m_data.key->challenge(masterSeed, m_data.challengeResponseKey);
+        m_data.masterSeed->setHash(masterSeed);
+        QByteArray response;
+        bool ok = m_data.key->challenge(masterSeed, response);
+        if (ok && !response.isEmpty()) {
+            m_data.challengeResponseKey->setHash(response);
+        }
+        return ok;
     }
     return false;
 }
@@ -679,7 +690,7 @@ bool Database::setKey(const QSharedPointer<const CompositeKey>& key,
 
     if (!key) {
         m_data.key.reset();
-        m_data.transformedMasterKey = {};
+        m_data.transformedMasterKey.reset(new PasswordKey());
         m_data.hasKey = false;
         return true;
     }
@@ -689,22 +700,29 @@ bool Database::setKey(const QSharedPointer<const CompositeKey>& key,
         Q_ASSERT(!m_data.kdf->seed().isEmpty());
     }
 
-    QByteArray oldTransformedMasterKey = m_data.transformedMasterKey;
+    PasswordKey oldTransformedMasterKey;
+    if (m_data.hasKey) {
+        oldTransformedMasterKey.setHash(m_data.transformedMasterKey->rawKey());
+    }
+
     QByteArray transformedMasterKey;
+
     if (!transformKey) {
-        transformedMasterKey = oldTransformedMasterKey;
+        transformedMasterKey = QByteArray(oldTransformedMasterKey.rawKey());
     } else if (!key->transform(*m_data.kdf, transformedMasterKey)) {
         return false;
     }
 
     m_data.key = key;
-    m_data.transformedMasterKey = transformedMasterKey;
+    if (!transformedMasterKey.isEmpty()) {
+        m_data.transformedMasterKey->setHash(transformedMasterKey);
+    }
     m_data.hasKey = true;
     if (updateChangedTime) {
         m_metadata->setMasterKeyChanged(Clock::currentDateTimeUtc());
     }
 
-    if (oldTransformedMasterKey != m_data.transformedMasterKey) {
+    if (oldTransformedMasterKey.rawKey() != m_data.transformedMasterKey->rawKey()) {
         markAsModified();
     }
 
@@ -720,15 +738,15 @@ bool Database::verifyKey(const QSharedPointer<CompositeKey>& key) const
 {
     Q_ASSERT(hasKey());
 
-    if (!m_data.challengeResponseKey.isEmpty()) {
+    if (!m_data.challengeResponseKey->rawKey().isEmpty()) {
         QByteArray result;
 
-        if (!key->challenge(m_data.masterSeed, result)) {
+        if (!key->challenge(m_data.masterSeed->rawKey(), result)) {
             // challenge failed, (YubiKey?) removed?
             return false;
         }
 
-        if (m_data.challengeResponseKey != result) {
+        if (m_data.challengeResponseKey->rawKey() != result) {
             // wrong response from challenged device(s)
             return false;
         }
@@ -893,7 +911,7 @@ bool Database::changeKdf(const QSharedPointer<Kdf>& kdf)
     }
 
     setKdf(kdf);
-    m_data.transformedMasterKey = transformedMasterKey;
+    m_data.transformedMasterKey->setHash(transformedMasterKey);
     markAsModified();
 
     return true;

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();

src/keys/PasswordKey.cpp

@@ -48,19 +48,29 @@ PasswordKey::~PasswordKey()
     }
 }
 
-QSharedPointer<PasswordKey> PasswordKey::fromRawKey(const QByteArray& rawKey)
-{
-    auto result = QSharedPointer<PasswordKey>::create();
-    std::memcpy(result->m_key, rawKey.data(), std::min(SHA256_SIZE, rawKey.size()));
-    return result;
-}
-
 QByteArray PasswordKey::rawKey() const
 {
+    if (!m_isInitialized) {
+        return {};
+    }
     return QByteArray::fromRawData(m_key, SHA256_SIZE);
 }
 
 void PasswordKey::setPassword(const QString& password)
 {
-    std::memcpy(m_key, CryptoHash::hash(password.toUtf8(), CryptoHash::Sha256).data(), SHA256_SIZE);
+    setHash(CryptoHash::hash(password.toUtf8(), CryptoHash::Sha256));
+}
+
+void PasswordKey::setHash(const QByteArray& hash)
+{
+    Q_ASSERT(hash.size() == SHA256_SIZE);
+    std::memcpy(m_key, hash.data(), std::min(SHA256_SIZE, hash.size()));
+    m_isInitialized = true;
+}
+
+QSharedPointer<PasswordKey> PasswordKey::fromRawKey(const QByteArray& rawKey)
+{
+    auto result = QSharedPointer<PasswordKey>::create();
+    result->setHash(rawKey);
+    return result;
 }

src/keys/PasswordKey.h

@@ -33,6 +33,7 @@ public:
     ~PasswordKey() override;
     QByteArray rawKey() const override;
     void setPassword(const QString& password);
+    void setHash(const QByteArray& hash);
 
     static QSharedPointer<PasswordKey> fromRawKey(const QByteArray& rawKey);
 
@@ -40,6 +41,7 @@ private:
     static constexpr int SHA256_SIZE = 32;
 
     char* m_key = nullptr;
+    bool m_isInitialized = false;
 };
 
 #endif // KEEPASSX_PASSWORDKEY_H