[Security] Add challenge-response auth with scrypt verifiers and stop storing plaintext passwords

Challenge-response authentication: the client derives a scrypt verifier
(RFC 7914, EVP_PBE_scrypt, N=32768, r=8, p=1) and authenticates with
HMAC-SHA256(key, nonce), so neither the password nor its hash is
transmitted. The stored format becomes
"$scrypt$<n>$<r>$<p>$<salt>$<verifier>" and Response_PasswordSalt
now carries the cost parameters. Strict servers only accept scrypt
verifiers; legacy accounts are migrated after a successful login.

Fix #344 for challenge-response servers: a saved profile stores the
derived verifier under the password key instead of the plaintext password.
The connect dialog loads it without revealing it, autoconnect passes it
through, the change-password dialog no longer prefills the old password
field with it, and the client only persists the verifier when
"Save password" is checked.

Took 3 minutes

Took 1 minute

Took 10 seconds

Took 7 minutes

cockatrice/src/client/network/connection_controller/remote_connection_controller.cpp

@@ -83,6 +83,9 @@ void ConnectionController::wireClientSignals()
 
     connect(remoteClient, &RemoteClient::sigPromptForForgotPasswordChallenge, this,
             &ConnectionController::onPromptForgotPasswordChallenge);
+
+    connect(remoteClient, &RemoteClient::sigPasswordVerifierReady, this,
+            &ConnectionController::onPasswordVerifierReady);
 }
 
 void ConnectionController::connectToServer()
@@ -91,16 +94,36 @@ void ConnectionController::connectToServer()
     connect(dlgConnect, &DlgConnect::sigStartForgotPasswordRequest, this, &ConnectionController::forgotPasswordRequest);
 
     if (dlgConnect->exec()) {
+        pendingSaveName = dlgConnect->getSaveName();
+        pendingSavePassword = dlgConnect->getSavePassword();
+        remoteClient->setStoredVerifier(dlgConnect->getStoredVerifier());
         remoteClient->connectToServer(dlgConnect->getHost(), static_cast<unsigned int>(dlgConnect->getPort()),
                                       dlgConnect->getPlayerName(), dlgConnect->getPassword());
     }
 }
 
+void ConnectionController::onPasswordVerifierReady(const QString &hostname,
+                                                   const QString &userName,
+                                                   const QString &verifier)
+{
+    Q_UNUSED(hostname);
+    Q_UNUSED(userName);
+    if (pendingSavePassword) {
+        SettingsCache::instance().servers().setServerPassword(pendingSaveName, verifier);
+    }
+}
+
 void ConnectionController::connectToServerDirect(const QString &host,
                                                  unsigned int port,
                                                  const QString &playerName,
-                                                 const QString &password)
+                                                 const QString &password,
+                                                 const QString &storedVerifier,
+                                                 const QString &saveName,
+                                                 bool savePassword)
 {
+    pendingSaveName = saveName;
+    pendingSavePassword = savePassword;
+    remoteClient->setStoredVerifier(storedVerifier);
     remoteClient->connectToServer(host, port, playerName, password);
 }
 

cockatrice/src/client/network/connection_controller/remote_connection_controller.h

@@ -35,8 +35,13 @@ public:
     void registerToServer();
     void forgotPasswordRequest();
     void connectToServer();
-    void
-    connectToServerDirect(const QString &host, unsigned int port, const QString &playerName, const QString &password);
+    void connectToServerDirect(const QString &host,
+                               unsigned int port,
+                               const QString &playerName,
+                               const QString &password,
+                               const QString &storedVerifier = QString(),
+                               const QString &saveName = QString(),
+                               bool savePassword = false);
     void disconnectFromServer();
 
     void refreshWindowTitle()
@@ -81,6 +86,9 @@ private slots:
     void onPromptForgotPasswordReset();
     void onPromptForgotPasswordChallenge();
 
+    // Persists the derived scrypt verifier after a successful challenge-response login
+    void onPasswordVerifierReady(const QString &hostname, const QString &userName, const QString &verifier);
+
 private:
     void wireClientSignals();
     void updateWindowTitle();
@@ -97,6 +105,10 @@ private:
 
     // Kept as a member so the forgot-password signal can be wired to it
     DlgConnect *dlgConnect{nullptr};
+
+    // Captured from the connect dialog when a connection is initiated
+    QString pendingSaveName;
+    bool pendingSavePassword{false};
 };
 
 #endif // COCKATRICE_REMOTE_CONNECTION_CONTROLLER_H

cockatrice/src/interface/widgets/dialogs/dlg_connect.cpp

@@ -273,9 +273,15 @@ void DlgConnect::updateDisplayInfo(const QString &saveName)
     playernameEdit->setText(_data.at(3));
     playernameEdit->setFocus();
     savePasswordCheckBox->setChecked(savePasswordStatus);
+    storedVerifier.clear();
 
     if (savePasswordStatus) {
-        passwordEdit->setText(_data.at(4));
+        const QString stored = _data.at(4);
+        if (stored.startsWith("$")) {
+            storedVerifier = stored;
+        } else {
+            passwordEdit->setText(stored);
+        }
     }
 
     if (!_data.at(6).isEmpty()) {
@@ -301,6 +307,7 @@ void DlgConnect::newHostSelected(bool state)
         portEdit->setDisabled(false);
         playernameEdit->clear();
         passwordEdit->clear();
+        storedVerifier.clear();
         saveEdit->clear();
         saveEdit->setPlaceholderText(tr("Unique Server Name"));
         saveEdit->setDisabled(false);
@@ -333,10 +340,13 @@ void DlgConnect::actOk()
         }
 
         servers.addNewServer(saveEdit->text().trimmed(), hostEdit->text().trimmed(), portEdit->text().trimmed(),
-                             playernameEdit->text().trimmed(), passwordEdit->text(), savePasswordCheckBox->isChecked());
+                             playernameEdit->text().trimmed(),
+                             passwordEdit->text().isEmpty() ? storedVerifier : passwordEdit->text(),
+                             savePasswordCheckBox->isChecked());
     } else {
         servers.updateExistingServer(saveEdit->text().trimmed(), hostEdit->text().trimmed(), portEdit->text().trimmed(),
-                                     playernameEdit->text().trimmed(), passwordEdit->text(),
+                                     playernameEdit->text().trimmed(),
+                                     passwordEdit->text().isEmpty() ? storedVerifier : passwordEdit->text(),
                                      savePasswordCheckBox->isChecked());
     }
 

cockatrice/src/interface/widgets/dialogs/dlg_connect.h

@@ -10,6 +10,7 @@
 #include "../interface/widgets/server/handle_public_servers.h"
 #include "../interface/widgets/server/user/user_info_connection.h"
 
+#include <QCheckBox>
 #include <QDialog>
 #include <QLineEdit>
 #include <libcockatrice/utility/macros.h>
@@ -47,6 +48,19 @@ public:
     {
         return passwordEdit->text();
     }
+    //! \brief Stored "$scrypt$..." verifier for challenge-response servers (never the plaintext password).
+    [[nodiscard]] QString getStoredVerifier() const
+    {
+        return storedVerifier;
+    }
+    [[nodiscard]] QString getSaveName() const
+    {
+        return saveEdit->text();
+    }
+    [[nodiscard]] bool getSavePassword() const
+    {
+        return savePasswordCheckBox->isChecked();
+    }
 
 public slots:
     void downloadThePublicServers();
@@ -77,6 +91,7 @@ private:
     QPushButton *btnConnect, *btnForgotPassword, *btnRefreshServers, *btnDeleteServer;
     QMap<QString, std::pair<QString, UserConnection_Information>> savedHostList;
     HandlePublicServers *hps;
+    QString storedVerifier;
     const QString placeHolderText = tr("Downloading...");
 };
 #endif

cockatrice/src/interface/widgets/dialogs/dlg_edit_password.cpp

@@ -18,7 +18,10 @@ DlgEditPassword::DlgEditPassword(QWidget *parent) : QDialog(parent)
 
     auto &servers = SettingsCache::instance().servers();
     if (servers.getSavePassword()) {
-        oldPasswordEdit->setText(servers.getPassword());
+        const QString stored = servers.getPassword();
+        if (!stored.startsWith("$")) {
+            oldPasswordEdit->setText(stored);
+        }
     }
 
     oldPasswordLabel->setBuddy(oldPasswordEdit);

cockatrice/src/interface/widgets/server/user/user_info_box.cpp

@@ -283,7 +283,9 @@ void UserInfoBox::changePassword(const QString &oldPassword, const QString &newP
 {
     Command_AccountPassword cmd;
     cmd.set_old_password(oldPassword.toStdString());
-    if (client->getServerSupportsPasswordHash()) {
+    if (client->getServerSupportsChallengeResponse()) {
+        cmd.set_hashed_new_password(PasswordHasher::generatePasswordVerifier(newPassword).toStdString());
+    } else if (client->getServerSupportsPasswordHash()) {
         auto passwordSalt = PasswordHasher::generateRandomSalt();
         QString hashedPassword = PasswordHasher::computeHash(newPassword, passwordSalt);
         cmd.set_hashed_new_password(hashedPassword.toStdString());

cockatrice/src/interface/window_main.cpp

@@ -871,8 +871,9 @@ void MainWindow::changeEvent(QEvent *event)
                        !startupDestinationConnectsToServer()) {
                 qCInfo(WindowMainStartupAutoconnectLog) << "Attempting auto-connect...";
                 DlgConnect dlg(this);
-                connectionController->connectToServerDirect(dlg.getHost(), static_cast<unsigned int>(dlg.getPort()),
-                                                            dlg.getPlayerName(), dlg.getPassword());
+                connectionController->connectToServerDirect(
+                    dlg.getHost(), static_cast<unsigned int>(dlg.getPort()), dlg.getPlayerName(), dlg.getPassword(),
+                    dlg.getStoredVerifier(), dlg.getSaveName(), dlg.getSavePassword());
             }
         }
     }