[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 +94,32 @@ 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 &verifier)
+{
+    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
+    void connectToServerDirect(const QString &host,
-    connectToServerDirect(const QString &host, unsigned int port, const QString &playerName, const QString &password);
+                               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 &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);
@@ -326,6 +333,11 @@ void DlgConnect::actOk()
 {
     ServersSettings &servers = SettingsCache::instance().servers();
 
+    // Never write a newly typed plaintext password to disk when a verifier is already stored:
+    // the typed value is used for this connection and a fresh verifier is persisted after a
+    // successful login. Without a stored verifier we keep the previous (plaintext legacy) behavior.
+    const QString passwordToSave = storedVerifier.isEmpty() ? passwordEdit->text() : storedVerifier;
+
     if (newHostButton->isChecked()) {
         if (saveEdit->text().isEmpty()) {
             QMessageBox::critical(this, tr("Connection Warning"), tr("You need to name your new connection profile."));
@@ -333,10 +345,10 @@ void DlgConnect::actOk()
         }
 
         servers.addNewServer(saveEdit->text().trimmed(), hostEdit->text().trimmed(), portEdit->text().trimmed(),
-                             playernameEdit->text().trimmed(), passwordEdit->text(), savePasswordCheckBox->isChecked());
+                             playernameEdit->text().trimmed(), passwordToSave, savePasswordCheckBox->isChecked());
     } else {
         servers.updateExistingServer(saveEdit->text().trimmed(), hostEdit->text().trimmed(), portEdit->text().trimmed(),
-                                     playernameEdit->text().trimmed(), passwordEdit->text(),
+                                     playernameEdit->text().trimmed(), passwordToSave,
                                      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()),
+                connectionController->connectToServerDirect(
-                                                            dlg.getPlayerName(), dlg.getPassword());
+                    dlg.getHost(), static_cast<unsigned int>(dlg.getPort()), dlg.getPlayerName(), dlg.getPassword(),
+                    dlg.getStoredVerifier(), dlg.getSaveName(), dlg.getSavePassword());
             }
         }
     }

libcockatrice_network/libcockatrice/network/client/abstract/abstract_client.cpp

@@ -22,7 +22,8 @@
 #include <libcockatrice/protocol/pending_command.h>
 
 AbstractClient::AbstractClient(QObject *parent)
-    : QObject(parent), nextCmdId(0), status(StatusDisconnected), serverSupportsPasswordHash(false)
+    : QObject(parent), nextCmdId(0), status(StatusDisconnected), serverSupportsPasswordHash(false),
+      serverSupportsChallengeResponse(false)
 {
     qRegisterMetaType<QVariant>("QVariant");
     qRegisterMetaType<CommandContainer>("CommandContainer");

libcockatrice_network/libcockatrice/network/client/abstract/abstract_client.h

@@ -117,6 +117,7 @@ protected:
     QMap<int, PendingCommand *> pendingCommands;
     QString userName, password, email, country, realName, token;
     bool serverSupportsPasswordHash;
+    bool serverSupportsChallengeResponse;
     void setStatus(ClientStatus _status);
     int getNewCmdId()
     {
@@ -150,6 +151,10 @@ public:
     {
         return serverSupportsPasswordHash;
     }
+    bool getServerSupportsChallengeResponse() const
+    {
+        return serverSupportsChallengeResponse;
+    }
     const QString &getUserName() const
     {
         return userName;

libcockatrice_network/libcockatrice/network/client/remote/remote_client.cpp

@@ -27,7 +27,8 @@ static const unsigned int protocolVersion = 14;
 
 RemoteClient::RemoteClient(QObject *parent, INetworkSettingsProvider *_networkSettingsProvider)
     : AbstractClient(parent), networkSettingsProvider(_networkSettingsProvider), timeRunning(0), lastDataReceived(0),
-      messageInProgress(false), handshakeStarted(false), usingWebSocket(false), messageLength(0), hashedPassword()
+      messageInProgress(false), handshakeStarted(false), usingWebSocket(false), messageLength(0), hashedPassword(),
+      passwordNeedsMigration(false)
 {
 
     clearNewClientFeatures();
@@ -114,6 +115,8 @@ void RemoteClient::processServerIdentificationEvent(const Event_ServerIdentifica
         return;
     }
     serverSupportsPasswordHash = event.server_options() & Event_ServerIdentification::SupportsPasswordHash;
+    serverSupportsChallengeResponse =
+        event.server_options() & Event_ServerIdentification::SupportsChallengeResponseAuth;
 
     if (getStatus() == StatusRequestingForgotPassword) {
         Command_ForgotPasswordRequest cmdForgotPasswordRequest;
@@ -130,7 +133,13 @@ void RemoteClient::processServerIdentificationEvent(const Event_ServerIdentifica
         cmdForgotPasswordReset.set_user_name(userName.toStdString());
         cmdForgotPasswordReset.set_clientid(getSrvClientID(lastHostname).toStdString());
         cmdForgotPasswordReset.set_token(token.toStdString());
-        if (!password.isEmpty() && serverSupportsPasswordHash) {
+        if (!password.isEmpty() && serverSupportsChallengeResponse) {
+            hashedPassword = PasswordHasher::generatePasswordVerifier(password);
+            // Only this branch yields a challenge-response verifier worth persisting; the
+            // legacy-hash and plaintext branches below must not be saved under the password key.
+            derivedVerifier = hashedPassword;
+            cmdForgotPasswordReset.set_hashed_new_password(hashedPassword.toStdString());
+        } else if (!password.isEmpty() && serverSupportsPasswordHash) {
             auto passwordSalt = PasswordHasher::generateRandomSalt();
             hashedPassword = PasswordHasher::computeHash(password, passwordSalt);
             cmdForgotPasswordReset.set_hashed_new_password(hashedPassword.toStdString());
@@ -158,7 +167,10 @@ void RemoteClient::processServerIdentificationEvent(const Event_ServerIdentifica
     if (getStatus() == StatusRegistering) {
         Command_Register cmdRegister;
         cmdRegister.set_user_name(userName.toStdString());
-        if (!password.isEmpty() && serverSupportsPasswordHash) {
+        if (!password.isEmpty() && serverSupportsChallengeResponse) {
+            hashedPassword = PasswordHasher::generatePasswordVerifier(password);
+            cmdRegister.set_hashed_password(hashedPassword.toStdString());
+        } else if (!password.isEmpty() && serverSupportsPasswordHash) {
             auto passwordSalt = PasswordHasher::generateRandomSalt();
             hashedPassword = PasswordHasher::computeHash(password, passwordSalt);
             cmdRegister.set_hashed_password(hashedPassword.toStdString());
@@ -223,7 +235,9 @@ Command_Login RemoteClient::generateCommandLogin()
 
 void RemoteClient::doLogin()
 {
-    if (!password.isEmpty() && serverSupportsPasswordHash) {
+    if ((!password.isEmpty() || !storedVerifier.isEmpty()) && serverSupportsChallengeResponse) {
+        doRequestPasswordSalt(); // ask salt + nonce to build the challenge response
+    } else if (!password.isEmpty() && serverSupportsPasswordHash) {
         //! \todo Store and log in using stored hashed password.
         if (hashedPassword.isEmpty()) {
             doRequestPasswordSalt(); // ask salt to create hashedPassword, then log in
@@ -257,6 +271,30 @@ void RemoteClient::doHashedLogin()
     sendCommand(pend);
 }
 
+void RemoteClient::doSubmitPasswordVerifier()
+{
+    pendingVerifier = PasswordHasher::generatePasswordVerifier(password);
+    Command_SubmitPasswordVerifier cmdSubmitVerifier;
+    cmdSubmitVerifier.set_password_verifier(pendingVerifier.toStdString());
+
+    PendingCommand *pend = prepareSessionCommand(cmdSubmitVerifier);
+    connect(pend, &PendingCommand::finished, this, &RemoteClient::submitPasswordVerifierResponse);
+    sendCommand(pend);
+}
+
+void RemoteClient::submitPasswordVerifierResponse(const Response &response)
+{
+    if (response.response_code() == Response::RespOk) {
+        qCDebug(RemoteClientLog) << "Password verifier migrated successfully";
+        if (!pendingVerifier.isEmpty()) {
+            emit sigPasswordVerifierReady(pendingVerifier);
+            pendingVerifier.clear();
+        }
+    } else {
+        qCWarning(RemoteClientLog) << "Failed to migrate password verifier:" << response.response_code();
+    }
+}
+
 void RemoteClient::processConnectionClosedEvent(const Event_ConnectionClosed & /*event*/)
 {
     doDisconnectFromServer();
@@ -269,7 +307,59 @@ void RemoteClient::passwordSaltResponse(const Response &response)
         auto passwordSalt = QString::fromStdString(resp.password_salt());
         if (passwordSalt.isEmpty()) { // the server does not recognize the user but allows them to enter unregistered
             password.clear();         // the password will not be used
+            storedVerifier.clear();
             doLogin();
+        } else if (serverSupportsChallengeResponse && resp.has_nonce()) {
+            const QByteArray nonce = QByteArray::fromStdString(resp.nonce());
+            QByteArray key;
+            if (resp.needs_migration()) {
+                // The account still uses the legacy format; the legacy full hash
+                // is only derivable from the plaintext password.
+                if (password.isEmpty()) {
+                    emit loginError(Response::RespClientUpdateRequired,
+                                    QStringLiteral("This account must be logged in with its password once."), 0, {});
+                    return;
+                }
+                key = PasswordHasher::computeHash(password, passwordSalt).toUtf8();
+            } else if (!password.isEmpty()) {
+                // A hostile server must not be able to make us run or allocate for
+                // unreasonable scrypt parameters.
+                const int n = resp.has_n() ? resp.n() : SCRYPT_N;
+                const int r = resp.has_r() ? resp.r() : SCRYPT_R;
+                const int p = resp.has_p() ? resp.p() : SCRYPT_P;
+                if (!PasswordHasher::costParamsAreSane(n, r, p)) {
+                    emit loginError(Response::RespClientUpdateRequired,
+                                    QStringLiteral("The server requested unreasonable scrypt cost parameters."), 0, {});
+                    return;
+                }
+                key = PasswordHasher::deriveKey(password, QByteArray::fromBase64(passwordSalt.toUtf8()), n, r, p);
+                if (key.isEmpty()) {
+                    emit loginError(Response::RespClientUpdateRequired, QStringLiteral("Unable to derive verifier."), 0,
+                                    {});
+                    return;
+                }
+                derivedVerifier = QString("$scrypt$%1$%2$%3$%4$%5")
+                                      .arg(n)
+                                      .arg(r)
+                                      .arg(p)
+                                      .arg(passwordSalt)
+                                      .arg(QString(key.toBase64()));
+            } else if (!storedVerifier.isEmpty()) {
+                const PasswordVerifier verifier = PasswordHasher::parsePasswordVerifier(storedVerifier);
+                if (!verifier.isValid) {
+                    emit loginError(Response::RespClientUpdateRequired, QStringLiteral("Stored verifier is invalid."),
+                                    0, {});
+                    return;
+                }
+                key = verifier.verifier;
+            } else {
+                emit loginError(Response::RespLoginNeeded, {}, 0, {});
+                return;
+            }
+            passwordNeedsMigration = resp.needs_migration();
+            const QByteArray responseBytes = PasswordHasher::computeResponse(key, nonce);
+            hashedPassword = "$challenge$" + QString(nonce.toBase64()) + "$" + QString(responseBytes.toBase64());
+            doHashedLogin();
         } else {
             hashedPassword = PasswordHasher::computeHash(password, passwordSalt);
             doHashedLogin();
@@ -294,6 +384,14 @@ void RemoteClient::loginResponse(const Response &response)
         setStatus(StatusLoggedIn);
         emit userInfoChanged(resp.user_info());
 
+        if (passwordNeedsMigration) {
+            // The account still used the legacy password format; upgrade it to scrypt.
+            doSubmitPasswordVerifier();
+        } else if (!derivedVerifier.isEmpty()) {
+            emit sigPasswordVerifierReady(derivedVerifier);
+            derivedVerifier.clear();
+        }
+
         QList<ServerInfo_User> buddyList;
         for (int i = resp.buddy_list_size() - 1; i >= 0; --i) {
             buddyList.append(resp.buddy_list(i));
@@ -550,6 +648,8 @@ void RemoteClient::doDisconnectFromServer()
         websocket->close();
     }
     socket->close();
+    derivedVerifier.clear();
+    pendingVerifier.clear();
 }
 
 void RemoteClient::ping()
@@ -712,6 +812,12 @@ void RemoteClient::submitForgotPasswordResetResponse(const Response &response)
 {
     if (response.response_code() == Response::RespOk) {
         emit sigForgotPasswordSuccess();
+        // Persist only a real scrypt verifier; a legacy hash must not be stored under
+        // the password key, where it would break future challenge-response logins.
+        if (!derivedVerifier.isEmpty()) {
+            emit sigPasswordVerifierReady(derivedVerifier);
+            derivedVerifier.clear();
+        }
     } else {
         emit sigForgotPasswordError();
     }

libcockatrice_network/libcockatrice/network/client/remote/remote_client.h

@@ -54,6 +54,11 @@ signals:
                                                   unsigned int port,
                                                   const QString &_userName,
                                                   const QString &_email);
+    //! \brief Emitted once a scrypt verifier for the given account is known and
+    //! can be persisted instead of the plaintext password. The receiving side
+    //! should only store it for the connection it is currently negotiating, so
+    //! the hostname and user name are intentionally not part of the signal.
+    void sigPasswordVerifierReady(const QString &verifier);
 private slots:
     void slotConnected();
     void readData();
@@ -80,6 +85,8 @@ private slots:
     void doLogin();
     void doHashedLogin();
     Command_Login generateCommandLogin();
+    void doSubmitPasswordVerifier();
+    void submitPasswordVerifierResponse(const Response &response);
     void doDisconnectFromServer();
     void doActivateToServer(const QString &_token);
     void doRequestForgotPasswordToServer(const QString &hostname, unsigned int port, const QString &_userName);
@@ -111,6 +118,14 @@ private:
     QString lastHostname;
     unsigned int lastPort;
     QString hashedPassword;
+    bool passwordNeedsMigration;
+    //! \brief A previously stored "$scrypt$..." verifier used to authenticate
+    //! without the plaintext password.
+    QString storedVerifier;
+    //! \brief Verifier derived during the current login, persisted after success.
+    QString derivedVerifier;
+    //! \brief Verifier sent for migration, persisted once the server accepts it.
+    QString pendingVerifier;
 
     QString getSrvClientID(const QString &_hostname);
     bool newMissingFeatureFound(const QString &_serversMissingFeatures);
@@ -149,6 +164,12 @@ public:
     }
     void
     connectToServer(const QString &hostname, unsigned int port, const QString &_userName, const QString &_password);
+    //! \brief Provide a stored "$scrypt$..." verifier so the client can
+    //! authenticate without the plaintext password.
+    void setStoredVerifier(const QString &verifier)
+    {
+        storedVerifier = verifier;
+    }
     void registerToServer(const QString &hostname,
                           unsigned int port,
                           const QString &_userName,

libcockatrice_network/libcockatrice/network/server/remote/server.h

@@ -85,6 +85,11 @@ public:
     {
         return QMap<QString, bool>();
     }
+    /** @brief True when only challenge-response logins are accepted (strict mode). */
+    virtual bool requiresChallengeResponseAuth() const
+    {
+        return false;
+    }
     void addClient(Server_ProtocolHandler *player);
     void removeClient(Server_ProtocolHandler *player);
     QList<QString> getOnlineModeratorList() const;

libcockatrice_network/libcockatrice/network/server/remote/server_database_interface.h

@@ -40,6 +40,14 @@ public:
     {
         return {};
     }
+    virtual QString getUserPasswordData(const QString & /* user */)
+    {
+        return {};
+    }
+    virtual bool submitPasswordVerifier(const QString & /* user */, const QString & /* passwordVerifier */)
+    {
+        return false;
+    }
     virtual QMap<QString, ServerInfo_User> getBuddyList(const QString & /* name */)
     {
         return QMap<QString, ServerInfo_User>();

libcockatrice_network/libcockatrice/network/server/remote/server_protocolhandler.cpp

@@ -44,6 +44,22 @@ Server_ProtocolHandler::~Server_ProtocolHandler()
 {
 }
 
+void Server_ProtocolHandler::setAuthNonce(const QByteArray &nonce)
+{
+    authNonce = nonce;
+    authNonceCreated = QDateTime::currentDateTimeUtc();
+}
+
+bool Server_ProtocolHandler::isAuthNonceValid(const QByteArray &nonce) const
+{
+    return !authNonce.isEmpty() && authNonce == nonce && authNonceCreated.secsTo(QDateTime::currentDateTimeUtc()) < 60;
+}
+
+void Server_ProtocolHandler::clearAuthNonce()
+{
+    authNonce.clear();
+}
+
 // This function must only be called from the thread this object lives in.
 // Except when the server is shutting down.
 // The thread must not hold any server locks when calling this (e.g. clientsLock, roomsLock).
@@ -507,6 +523,16 @@ Response::ResponseCode Server_ProtocolHandler::cmdLogin(const Command_Login &cmd
         return Response::RespContextError;
     }
 
+    // In strict mode only challenge-response logins are accepted.
+    if (server->requiresChallengeResponseAuth() &&
+        (!cmd.has_hashed_password() || cmd.hashed_password().rfind("$challenge$", 0) != 0)) {
+        auto *re = new Response_Login;
+        re->set_denied_reason_str("Client upgrade required");
+        re->add_missing_features("challenge_response_auth");
+        rc.setResponseExtension(re);
+        return Response::RespClientUpdateRequired;
+    }
+
     // check client feature set against server feature set
     FeatureSet features;
     QMap<QString, bool> receivedClientFeatures;

libcockatrice_network/libcockatrice/network/server/remote/server_protocolhandler.h

@@ -4,6 +4,8 @@
 #include "server.h"
 #include "server_abstractuserinterface.h"
 
+#include <QByteArray>
+#include <QDateTime>
 #include <QObject>
 #include <libcockatrice/protocol/pb/response.pb.h>
 #include <libcockatrice/protocol/pb/server_message.pb.h>
@@ -55,6 +57,8 @@ protected:
     bool acceptsUserListChanges;
     bool acceptsRoomListChanges;
     bool idleClientWarningSent;
+    QByteArray authNonce;
+    QDateTime authNonceCreated;
     virtual void logDebugMessage(const QString & /* message */)
     {
     }
@@ -124,6 +128,13 @@ public:
         return databaseInterface;
     }
 
+    /** @brief Store a fresh challenge nonce for the next challenge-response login attempt. */
+    void setAuthNonce(const QByteArray &nonce);
+    /** @brief True if nonce matches the pending one and was issued less than 60 seconds ago. */
+    bool isAuthNonceValid(const QByteArray &nonce) const;
+    /** @brief Invalidate the pending nonce (single-use). */
+    void clearAuthNonce();
+
     int getLastCommandTime() const
     {
         return timeRunning - lastDataReceived;

libcockatrice_protocol/libcockatrice/protocol/featureset.cpp

@@ -25,7 +25,8 @@ void FeatureSet::initalizeFeatureList(QMap<QString, bool> &_featureList)
     _featureList.insert("idle_client", false);
     _featureList.insert("forgot_password", false);
     _featureList.insert("websocket", false);
-    // featureList.insert("hashed_password_login", false);
+    _featureList.insert("hashed_password_login", false);
+    _featureList.insert("challenge_response_auth", false);
     // These are temp to force users onto a newer client
     _featureList.insert("2.7.0_min_version", false);
     _featureList.insert("2.8.0_min_version", false);

libcockatrice_protocol/libcockatrice/protocol/pb/event_server_identification.proto

@@ -8,6 +8,7 @@ message Event_ServerIdentification {
     enum ServerOptions {
         NoOptions = 0;
         SupportsPasswordHash = 1;
+        SupportsChallengeResponseAuth = 2;
     }
     optional string server_name = 1;
     optional string server_version = 2;

libcockatrice_protocol/libcockatrice/protocol/pb/response_password_salt.proto

@@ -6,4 +6,14 @@ message Response_PasswordSalt {
         optional Response_PasswordSalt ext = 1017;
     }
     optional string password_salt = 1;
+    // scrypt cost parameters for password_salt. Absent/zero for legacy accounts.
+    optional int32 n = 2;
+    optional int32 r = 3;
+    optional int32 p = 4;
+    // Server-generated challenge. When present the client must authenticate
+    // with a challenge-response instead of transmitting the password hash.
+    optional bytes nonce = 5;
+    // True when the account still uses the legacy password format and should
+    // be migrated to the scrypt format after a successful login.
+    optional bool needs_migration = 6;
 }

libcockatrice_protocol/libcockatrice/protocol/pb/session_commands.proto

@@ -28,6 +28,7 @@ message SessionCommand {
         FORGOT_PASSWORD_CHALLENGE = 1023;
         REQUEST_PASSWORD_SALT = 1024;
         SET_CARD_ART_PARAMS = 1025;
+        SUBMIT_PASSWORD_VERIFIER = 1026;
         REPLAY_LIST = 1100;
         REPLAY_DOWNLOAD = 1101;
         REPLAY_MODIFY_MATCH = 1102;
@@ -223,3 +224,14 @@ message Command_SetCardArtParams {
     optional double vertical_offset = 5;
     optional double zoom = 6;
 }
+
+// Client uploads the new password verifier to migrate a legacy account
+// after a successful challenge-response login. Idempotent; only applies
+// to accounts still using the legacy password format.
+message Command_SubmitPasswordVerifier {
+    extend SessionCommand {
+        optional Command_SubmitPasswordVerifier ext = 1026;
+    }
+    // Full verifier string to store, e.g. "$scrypt$32768$8$1$<salt>$<verifier>"
+    required string password_verifier = 1;
+}

libcockatrice_settings/libcockatrice/settings/servers_settings.cpp

@@ -146,6 +146,14 @@ void ServersSettings::setFPPlayerName(QString playerName)
     setValue(playerName, "fpPlayerName");
 }
 
+void ServersSettings::setServerPassword(const QString &saveName, const QString &password)
+{
+    const int index = getPrevioushostindex(saveName);
+    if (index >= 0) {
+        setValue(password, QString("password%1").arg(index), "server", "server_details");
+    }
+}
+
 QString ServersSettings::getFPPlayerName(QString defaultName) const
 {
     QVariant name = getValue("fpPlayerName");

libcockatrice_settings/libcockatrice/settings/servers_settings.h

@@ -46,6 +46,8 @@ public:
     void setFPHostName(QString hostname);
     void setFPPort(QString port);
     void setFPPlayerName(QString playerName);
+    //! \brief Store a password (or a "$scrypt$..." verifier) for the given saved server.
+    void setServerPassword(const QString &saveName, const QString &password);
     void addNewServer(const QString &saveName,
                       const QString &serv,
                       const QString &port,

libcockatrice_utility/libcockatrice/utility/passwordhasher.cpp

@@ -2,6 +2,9 @@
 
 #include <QCryptographicHash>
 #include <libcockatrice/utility/cryptoutil.h>
+#include <openssl/crypto.h>
+#include <openssl/evp.h>
+#include <openssl/hmac.h>
 
 QString PasswordHasher::computeHash(const QString &password, const QString &salt)
 {
@@ -52,3 +55,114 @@ QString PasswordHasher::generateActivationToken()
 {
     return QString(CryptoUtil::randomBytes(16).toBase64().left(16));
 }
+
+QByteArray PasswordHasher::deriveKey(const QString &password, const QByteArray &salt, int n, int r, int p)
+{
+    QByteArray key(SCRYPT_VERIFIER_LENGTH, '\0');
+    const QByteArray passwordUtf8 = password.toUtf8();
+    // EVP_PBE_scrypt aborts unless maxmem covers the required working memory,
+    // which is roughly 128 * n * r bytes (plus the small Salsa20/8 block array).
+    const auto maxmem = static_cast<quint64>(128) * n * r + static_cast<quint64>(128) * r * p + 4096;
+    if (EVP_PBE_scrypt(passwordUtf8.constData(), passwordUtf8.size(),
+                       reinterpret_cast<const unsigned char *>(salt.constData()), salt.size(), n, r, p, maxmem,
+                       reinterpret_cast<unsigned char *>(key.data()), key.size()) != 1) {
+        return QByteArray();
+    }
+    return key;
+}
+
+bool PasswordHasher::costParamsAreSane(int n, int r, int p)
+{
+    // Bounds adopted during review: n in [1024, 2**20] and a power of two, r in [1, 32],
+    // p in [1, 16]. Anything else is rejected before we allocate or derive for it.
+    return n >= 1024 && n <= (1 << 20) && (n & (n - 1)) == 0 && r >= 1 && r <= 32 && p >= 1 && p <= 16;
+}
+
+QString PasswordHasher::generatePasswordVerifier(const QString &password)
+{
+    const QByteArray salt = CryptoUtil::randomBytes(SCRYPT_SALT_LENGTH);
+    const QByteArray verifier = deriveKey(password, salt, SCRYPT_N, SCRYPT_R, SCRYPT_P);
+    return QString("$scrypt$%1$%2$%3$%4$%5")
+        .arg(SCRYPT_N)
+        .arg(SCRYPT_R)
+        .arg(SCRYPT_P)
+        .arg(QString(salt.toBase64()))
+        .arg(QString(verifier.toBase64()));
+}
+
+PasswordVerifier PasswordHasher::parsePasswordVerifier(const QString &stored)
+{
+    PasswordVerifier result;
+    const QStringList parts = stored.split("$");
+    if (parts.size() != 7 || parts.at(1) != "scrypt") {
+        return result;
+    }
+
+    bool ok = false;
+    const int n = parts.at(2).toInt(&ok);
+    if (!ok) {
+        return result;
+    }
+    const int r = parts.at(3).toInt(&ok);
+    if (!ok) {
+        return result;
+    }
+    const int p = parts.at(4).toInt(&ok);
+    if (!ok || !costParamsAreSane(n, r, p)) {
+        return result;
+    }
+
+    const QByteArray salt = QByteArray::fromBase64(parts.at(5).toUtf8());
+    const QByteArray verifier = QByteArray::fromBase64(parts.at(6).toUtf8());
+    if (salt.isEmpty() || verifier.size() != SCRYPT_VERIFIER_LENGTH) {
+        return result;
+    }
+
+    result.format = PasswordFormat::Scrypt;
+    result.n = n;
+    result.r = r;
+    result.p = p;
+    result.salt = salt;
+    result.verifier = verifier;
+    result.isValid = true;
+    return result;
+}
+
+bool PasswordHasher::isLegacyFormat(const QString &stored)
+{
+    return !stored.startsWith("$");
+}
+
+bool PasswordHasher::verifyPassword(const QString &password, const QString &storedPasswordData)
+{
+    if (isLegacyFormat(storedPasswordData)) {
+        return storedPasswordData == computeHash(password, storedPasswordData.left(16));
+    }
+
+    const PasswordVerifier verifier = parsePasswordVerifier(storedPasswordData);
+    if (!verifier.isValid) {
+        return false;
+    }
+    const QByteArray derived = deriveKey(password, verifier.salt, verifier.n, verifier.r, verifier.p);
+    return !derived.isEmpty() && constantTimeEquals(derived, verifier.verifier);
+}
+
+QByteArray PasswordHasher::computeResponse(const QByteArray &key, const QByteArray &nonce)
+{
+    QByteArray response(EVP_MAX_MD_SIZE, '\0');
+    unsigned int responseLength = 0;
+    if (HMAC(EVP_sha256(), key.constData(), key.size(), reinterpret_cast<const unsigned char *>(nonce.constData()),
+             nonce.size(), reinterpret_cast<unsigned char *>(response.data()), &responseLength) == nullptr) {
+        qFatal("PasswordHasher::computeResponse: HMAC failed");
+    }
+    response.resize(responseLength);
+    return response;
+}
+
+bool PasswordHasher::constantTimeEquals(const QByteArray &a, const QByteArray &b)
+{
+    if (a.size() != b.size()) {
+        return false;
+    }
+    return CRYPTO_memcmp(a.constData(), b.constData(), a.size()) == 0;
+}

libcockatrice_utility/libcockatrice/utility/passwordhasher.h

@@ -1,14 +1,57 @@
 #ifndef PASSWORDHASHER_H
 #define PASSWORDHASHER_H
 
+#include <QByteArray>
 #include <QObject>
 
+// scrypt cost parameters used for newly created password verifiers. These match
+// the RFC 7914 recommended parameters for interactive use.
+constexpr int SCRYPT_N = 32768;
+constexpr int SCRYPT_R = 8;
+constexpr int SCRYPT_P = 1;
+constexpr int SCRYPT_SALT_LENGTH = 16;
+constexpr int SCRYPT_VERIFIER_LENGTH = 64;
+
+enum class PasswordFormat
+{
+    None = 0,
+    Scrypt
+};
+
+struct PasswordVerifier
+{
+    PasswordFormat format = PasswordFormat::None;
+    int n = 0;
+    int r = 0;
+    int p = 0;
+    QByteArray salt;
+    QByteArray verifier;
+    bool isValid = false;
+};
+
 class PasswordHasher
 {
 public:
     static QString computeHash(const QString &password, const QString &salt);
     static QString generateRandomSalt(const int len = 16);
     static QString generateActivationToken();
+
+    /** @brief Derive the scrypt verifier for the given password, salt and cost parameters. Empty on failure. */
+    static QByteArray deriveKey(const QString &password, const QByteArray &salt, int n, int r, int p);
+    /** @brief True if the scrypt cost parameters are acceptable for server and client use. */
+    static bool costParamsAreSane(int n, int r, int p);
+    /** @brief Build a "$scrypt$<n>$<r>$<p>$<salt>$<verifier>" string with a fresh random salt. */
+    static QString generatePasswordVerifier(const QString &password);
+    /** @brief Parse a stored "$scrypt$..." string into its components. */
+    static PasswordVerifier parsePasswordVerifier(const QString &stored);
+    /** @brief True if the stored value is not in the scrypt format (legacy salt+hash). */
+    static bool isLegacyFormat(const QString &stored);
+    /** @brief True if the password matches the stored credential, whether legacy salt+hash or scrypt. */
+    static bool verifyPassword(const QString &password, const QString &storedPasswordData);
+    /** @brief HMAC-SHA256 of nonce keyed with the password verifier, used for challenge-response logins. */
+    static QByteArray computeResponse(const QByteArray &key, const QByteArray &nonce);
+    /** @brief Constant-time byte comparison. */
+    static bool constantTimeEquals(const QByteArray &a, const QByteArray &b);
 };
 
 #endif

servatrice/migrations/servatrice_0036_to_0037.sql

@@ -0,0 +1,8 @@
+-- Servatrice db migration from version 36 to version 37
+
+-- The column must hold "$scrypt$<n>$<r>$<p>$<salt>$<verifier>" (up to ~255 chars) and arbitrary
+-- legacy base64 hashes, so it grows beyond the old 120-char size. varchar(255) is used as the
+-- column type is promotion-safe and avoids the row-format change ALGORITHM=INSTANT cannot do.
+ALTER TABLE `cockatrice_users` MODIFY `password_sha512` varchar(255) NOT NULL;
+
+UPDATE cockatrice_schema_version SET version=37 WHERE version=36;

servatrice/servatrice.ini.example

@@ -350,6 +350,22 @@ max_users_websocket=500
 ; Maximum number of users that can connect from the same IP address; useful to avoid bots, default is 4
 max_users_per_address=4
 
+; How strictly new authentication features are enforced.  Possible values:
+; * legacy: accounts that still use the legacy 1000-round SHA-512 hash keep logging in with it
+;           (they are served the legacy salt, never a challenge-response nonce) and are never
+;           auto-migrated to scrypt. Already-migrated scrypt rows keep logging in via
+;           challenge-response. New credentials may use either format;
+; * mixed: accept both legacy hashes and challenge-response authentication (default);
+; * strict: only accept challenge-response authentication from clients that support it,
+;           and reject plain password submissions.  Legacy accounts are migrated to scrypt
+;           automatically on their next successful login.
+;
+; Challenge-response verifiers are scrypt (RFC 7914, N=32768, r=8, p=1) stored as
+; "$scrypt$<n>$<r>$<p>$<salt>$<verifier>". The stored verifier is password-equivalent:
+; plaintext passwords never reach the client configuration and never go over the wire, but
+; a database dump yields credentials that can answer a login challenge directly.
+authentication_strictness=mixed
+
 ; You may want to allow an unlimited number of users from a trusted source. This setting can contain a
 ; comma-separed list of IP addresses which will allow an unlimited number of connections from each of the
 ; IP addresses listed (ignoring the max_users_per_address). Default is "127.0.0.1,::1"; example: "192.73.233.244,81.4.100.74"

servatrice/servatrice.sql

@@ -20,7 +20,7 @@ CREATE TABLE IF NOT EXISTS `cockatrice_schema_version` (
   PRIMARY KEY  (`version`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
 
-INSERT INTO cockatrice_schema_version VALUES(36);
+INSERT INTO cockatrice_schema_version VALUES(37);
 
 -- users and user data tables
 CREATE TABLE IF NOT EXISTS `cockatrice_users` (
@@ -28,7 +28,7 @@ CREATE TABLE IF NOT EXISTS `cockatrice_users` (
   `admin` tinyint(1) NOT NULL,
   `name` varchar(35) NOT NULL,
   `realname` varchar(255) NOT NULL,
-  `password_sha512` char(120) NOT NULL,
+  `password_sha512` varchar(255) NOT NULL,
   `email` varchar(255) NOT NULL,
   `country` char(2) NOT NULL,
   `avatar_bmp` mediumblob NOT NULL,

servatrice/src/servatrice.cpp

@@ -900,6 +900,18 @@ QString Servatrice::getRequiredFeatures() const
     return settingsCache->value("server/requiredfeatures", "").toString();
 }
 
+Servatrice::AuthenticationStrictness Servatrice::getAuthenticationStrictness() const
+{
+    const QString strictness = settingsCache->value("security/authentication_strictness", "mixed").toString();
+    if (strictness == "strict") {
+        return AuthenticationStrict;
+    }
+    if (strictness == "legacy") {
+        return AuthenticationLegacy;
+    }
+    return AuthenticationMixed;
+}
+
 QString Servatrice::getDBTypeString() const
 {
     if (QProcessEnvironment::systemEnvironment().contains("DATABASE_URL")) {

servatrice/src/servatrice.h

@@ -140,6 +140,12 @@ public:
         AuthenticationSql,
         AuthenticationPassword
     };
+    enum AuthenticationStrictness
+    {
+        AuthenticationLegacy,
+        AuthenticationMixed,
+        AuthenticationStrict
+    };
 private slots:
     void statusUpdate();
     void shutdownTimeout();
@@ -219,6 +225,10 @@ public:
     {
         return serverRequiredFeatureList;
     }
+    bool requiresChallengeResponseAuth() const override
+    {
+        return getAuthenticationStrictness() == AuthenticationStrict;
+    }
     QString getServerName() const;
     QString getLoginMessage() const override
     {
@@ -240,6 +250,7 @@ public:
     {
         return authenticationMethod;
     }
+    AuthenticationStrictness getAuthenticationStrictness() const;
     bool permitUnregisteredUsers() const override
     {
         return authenticationMethod != AuthenticationNone;

servatrice/src/servatrice_database_interface.cpp

@@ -356,6 +356,47 @@ AuthenticationResult Servatrice_DatabaseInterface::checkUserPassword(Server_Prot
                     qCWarning(DatabaseInterfaceLog) << "Login denied: user not active";
                     return UserIsInactive;
                 }
+
+                if (password.startsWith("$challenge$")) {
+                    // Challenge-response login: verify HMAC(stored_key, nonce) without
+                    // ever transmitting the stored credential or password hash.
+                    const QStringList parts = password.split("$");
+                    if (parts.size() != 4) {
+                        return NotLoggedIn;
+                    }
+                    const QByteArray nonce = QByteArray::fromBase64(parts.at(2).toUtf8());
+                    const QByteArray response = QByteArray::fromBase64(parts.at(3).toUtf8());
+                    if (nonce.isEmpty() || response.isEmpty() || !handler->isAuthNonceValid(nonce)) {
+                        return NotLoggedIn;
+                    }
+
+                    QByteArray key;
+                    if (PasswordHasher::isLegacyFormat(correctPasswordSha512)) {
+                        key = correctPasswordSha512.toUtf8();
+                    } else {
+                        // Design note: the stored scrypt verifier IS the challenge-response key, so a
+                        // database dump yields credentials that can answer a login challenge directly.
+                        // We deliberately accept this trade: it removes plaintext passwords from the
+                        // client config and from the wire, but does not protect against DB compromise.
+                        // A password-equivalent proof scheme (e.g. SRP-6a/OPAQUE) would be the proper
+                        // escalation and is out of scope here.
+                        const PasswordVerifier verifier = PasswordHasher::parsePasswordVerifier(correctPasswordSha512);
+                        if (!verifier.isValid) {
+                            return NotLoggedIn;
+                        }
+                        key = verifier.verifier;
+                    }
+
+                    const QByteArray expected = PasswordHasher::computeResponse(key, nonce);
+                    handler->clearAuthNonce();
+                    if (PasswordHasher::constantTimeEquals(expected, response)) {
+                        qCDebug(DatabaseInterfaceLog) << "Login accepted: challenge-response password right";
+                        return PasswordRight;
+                    }
+                    qCDebug(DatabaseInterfaceLog) << "Login denied: challenge-response password wrong";
+                    return NotLoggedIn;
+                }
+
                 QString hashedPassword;
                 if (passwordNeedsHash) {
                     hashedPassword = PasswordHasher::computeHash(password, correctPasswordSha512.left(16));
@@ -558,6 +599,48 @@ QString Servatrice_DatabaseInterface::getUserSalt(const QString &user)
     return {};
 }
 
+QString Servatrice_DatabaseInterface::getUserPasswordData(const QString &user)
+{
+    if (server->getAuthenticationMethod() != Servatrice::AuthenticationSql) {
+        return {};
+    }
+
+    checkSql();
+
+    QSqlQuery *query = prepareQuery("SELECT password_sha512 FROM {prefix}_users WHERE name = :name");
+    query->bindValue(":name", user);
+    if (!execSqlQuery(query)) {
+        return {};
+    }
+
+    if (!query->next()) {
+        return {};
+    }
+
+    return query->value(0).toString();
+}
+
+bool Servatrice_DatabaseInterface::submitPasswordVerifier(const QString &user, const QString &passwordVerifier)
+{
+    if (server->getAuthenticationMethod() != Servatrice::AuthenticationSql) {
+        return false;
+    }
+
+    checkSql();
+
+    // Only migrate accounts that still use the legacy format; the query is a no-op otherwise.
+    QSqlQuery *query = prepareQuery(
+        "update {prefix}_users set password_sha512 = :verifier where name = :user and password_sha512 not like '$%'");
+    query->bindValue(":verifier", passwordVerifier);
+    query->bindValue(":user", user);
+    if (!execSqlQuery(query)) {
+        qCWarning(DatabaseInterfaceLog) << "Failed to submit password verifier for user" << user << query->lastError();
+        return false;
+    }
+    // The guard makes a re-migration a no-op; only report success when a row was actually updated.
+    return query->numRowsAffected() > 0;
+}
+
 int Servatrice_DatabaseInterface::getUserIdInDB(const QString &name)
 {
     if (server->getAuthenticationMethod() == Servatrice::AuthenticationSql) {
@@ -1139,13 +1222,13 @@ bool Servatrice_DatabaseInterface::changeUserPassword(const QString &user,
         return false;
     }
 
-    const QString correctPasswordSha512 = passwordQuery->value(0).toString();
+    const QString storedPassword = passwordQuery->value(0).toString();
-    QString oldPasswordSha512 = oldPassword;
+    // oldPasswordNeedsHash means the client sent the old password in plaintext. Verify it
-    if (oldPasswordNeedsHash) {
+    // against whatever is stored: legacy salt+hash rows or already-migrated scrypt rows
-        QString salt = correctPasswordSha512.left(16);
+    // (which must NOT be re-hashed with a salt torn out of the "$scrypt$..." string).
-        oldPasswordSha512 = PasswordHasher::computeHash(oldPassword, salt);
+    const bool oldPasswordMatches = oldPasswordNeedsHash ? PasswordHasher::verifyPassword(oldPassword, storedPassword)
-    }
+                                                         : (oldPassword == storedPassword);
-    if (correctPasswordSha512 != oldPasswordSha512) {
+    if (!oldPasswordMatches) {
         return false;
     }
 

servatrice/src/servatrice_database_interface.h

@@ -13,7 +13,7 @@
 #include <server.h>
 #include <server_database_interface.h>
 
-#define DATABASE_SCHEMA_VERSION 36
+#define DATABASE_SCHEMA_VERSION 37
 
 class Servatrice;
 
@@ -65,6 +65,8 @@ public:
     bool activeUserExists(const QString &user) override;
     bool userExists(const QString &user) override;
     QString getUserSalt(const QString &user) override;
+    QString getUserPasswordData(const QString &user) override;
+    bool submitPasswordVerifier(const QString &user, const QString &passwordVerifier) override;
     int getUserIdInDB(const QString &name);
     QMap<QString, ServerInfo_User> getBuddyList(const QString &name) override;
     QMap<QString, ServerInfo_User> getIgnoreList(const QString &name) override;

servatrice/src/serversocketinterface.cpp

@@ -107,6 +107,7 @@
 #include <libcockatrice/protocol/pb/serverinfo_user.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_user_alt.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_user_session.pb.h>
+#include <libcockatrice/utility/cryptoutil.h>
 #include <libcockatrice/utility/passwordhasher.h>
 #include <libcockatrice/utility/string_limits.h>
 #include <libcockatrice/utility/warning_categories.h>
@@ -139,7 +140,14 @@ bool AbstractServerSocketInterface::initSession()
     identEvent.set_server_version(VERSION_STRING);
     identEvent.set_protocol_version(protocolVersion);
     if (servatrice->getAuthenticationMethod() == Servatrice::AuthenticationSql) {
-        identEvent.set_server_options(Event_ServerIdentification::SupportsPasswordHash);
+        // Challenge-response is advertised in every strictness mode: legacy accounts keep
+        // logging in with the legacy hash, but already-migrated scrypt rows are always
+        // served challenge-response (authentication_strictness only governs NEW credentials).
+        Event_ServerIdentification::ServerOptions serverOptions =
+            static_cast<Event_ServerIdentification::ServerOptions>(
+                Event_ServerIdentification::SupportsPasswordHash |
+                Event_ServerIdentification::SupportsChallengeResponseAuth);
+        identEvent.set_server_options(serverOptions);
     }
     SessionEvent *identSe = prepareSessionEvent(identEvent);
     sendProtocolItem(*identSe);
@@ -257,6 +265,8 @@ Response::ResponseCode AbstractServerSocketInterface::processExtendedSessionComm
             return cmdReportAddComment(cmd.GetExtension(Command_ReportAddComment::ext), rc);
         case SessionCommand::REPORT_DETAILS:
             return cmdReportDetails(cmd.GetExtension(Command_ReportDetails::ext), rc);
+        case SessionCommand::SUBMIT_PASSWORD_VERIFIER:
+            return cmdSubmitPasswordVerifier(cmd.GetExtension(Command_SubmitPasswordVerifier::ext), rc);
         default:
             return Response::RespFunctionNotAllowed;
     }
@@ -2461,6 +2471,11 @@ Response::ResponseCode AbstractServerSocketInterface::cmdRegisterAccount(const C
         password = QString::fromStdString(cmd.hashed_password());
     }
 
+    // Reject credential formats the configured authentication strictness does not accept.
+    if (!acceptsCredentialFormat(passwordNeedsHash, password)) {
+        return Response::RespClientUpdateRequired;
+    }
+
     bool requireEmailActivation = settingsCache->value("registration/requireemailactivation", true).toBool();
     bool regSucceeded = sqlInterface->registerUser(userName, realName, password, passwordNeedsHash, parsedEmailAddress,
                                                    country, !requireEmailActivation);
@@ -2507,6 +2522,21 @@ bool AbstractServerSocketInterface::tooManyRegistrationAttempts(const QString &i
     return false;
 }
 
+bool AbstractServerSocketInterface::acceptsCredentialFormat(bool passwordNeedsHash, const QString &password) const
+{
+    // "scryptFormat" means the client sent a derived verifier rather than a password to hash ourselves.
+    const bool scryptFormat = !passwordNeedsHash && !PasswordHasher::isLegacyFormat(password);
+
+    // The strictness mode governs how existing legacy accounts are served, not which new-credential
+    // formats are tolerated: a legacy-mode server must still accept scrypt verifiers, because clients
+    // derive them whenever challenge-response is advertised (and it must be, so already-migrated
+    // scrypt rows keep logging in). strict is the only mode that rejects legacy formats.
+    if (servatrice->getAuthenticationStrictness() == Servatrice::AuthenticationStrict) {
+        return scryptFormat;
+    }
+    return true; // legacy and mixed accept either format
+}
+
 Response::ResponseCode AbstractServerSocketInterface::cmdActivateAccount(const Command_Activate &cmd,
                                                                          ResponseContainer & /*rc*/)
 {
@@ -2841,6 +2871,11 @@ Response::ResponseCode AbstractServerSocketInterface::cmdAccountPassword(const C
         newPassword = QString::fromStdString(cmd.hashed_new_password());
     }
 
+    // Reject new credential formats the configured authentication strictness does not accept.
+    if (!acceptsCredentialFormat(newPasswordNeedsHash, newPassword)) {
+        return Response::RespClientUpdateRequired;
+    }
+
     QString userName = QString::fromStdString(userInfo->name());
     if (!databaseInterface->changeUserPassword(userName, oldPassword, true, newPassword, newPasswordNeedsHash)) {
         return Response::RespWrongPassword;
@@ -2978,6 +3013,11 @@ Response::ResponseCode AbstractServerSocketInterface::cmdForgotPasswordReset(con
         password = QString::fromStdString(cmd.hashed_new_password());
     }
 
+    // Reject new credential formats the configured authentication strictness does not accept.
+    if (!acceptsCredentialFormat(passwordNeedsHash, password)) {
+        return Response::RespClientUpdateRequired;
+    }
+
     if (sqlInterface->changeUserPassword(nameFromStdString(cmd.user_name()), password, passwordNeedsHash)) {
         if (servatrice->getEnableForgotPasswordAudit()) {
             sqlInterface->addAuditRecord(userName.simplified(), this->getAddress(), clientId.simplified(),
@@ -3038,8 +3078,8 @@ Response::ResponseCode AbstractServerSocketInterface::cmdRequestPasswordSalt(con
                                                                              ResponseContainer &rc)
 {
     const QString userName = nameFromStdString(cmd.user_name());
-    QString passwordSalt = sqlInterface->getUserSalt(userName);
+    const QString storedPasswordData = sqlInterface->getUserPasswordData(userName);
-    if (passwordSalt.isEmpty()) {
+    if (storedPasswordData.isEmpty()) {
         if (server->getRegOnlyServerEnabled()) {
             return Response::RespRegistrationRequired;
         } else {
@@ -3047,8 +3087,36 @@ Response::ResponseCode AbstractServerSocketInterface::cmdRequestPasswordSalt(con
             return Response::RespOk;
         }
     }
+
     auto *re = new Response_PasswordSalt;
-    re->set_password_salt(passwordSalt.toStdString());
+    if (PasswordHasher::isLegacyFormat(storedPasswordData)) {
+        re->set_password_salt(storedPasswordData.left(16).toStdString());
+        re->set_needs_migration(true);
+        // Legacy rows get a challenge-response nonce only outside legacy mode (there the client
+        // logs in with the legacy hash and the account is migrated). In legacy mode the row is
+        // served the legacy salt, since legacy mode only governs what NEW credentials are accepted.
+        if (servatrice->getAuthenticationStrictness() != Servatrice::AuthenticationLegacy) {
+            const QByteArray nonce = CryptoUtil::randomBytes(32);
+            setAuthNonce(nonce);
+            re->set_nonce(nonce.constData(), nonce.size());
+        }
+    } else {
+        const PasswordVerifier verifier = PasswordHasher::parsePasswordVerifier(storedPasswordData);
+        if (!verifier.isValid) {
+            delete re;
+            return Response::RespContextError;
+        }
+        re->set_password_salt(QString(verifier.salt.toBase64()).toStdString());
+        re->set_n(verifier.n);
+        re->set_r(verifier.r);
+        re->set_p(verifier.p);
+        re->set_needs_migration(false);
+        // scrypt rows are served challenge-response in every mode so migrated accounts never lock out.
+        const QByteArray nonce = CryptoUtil::randomBytes(32);
+        setAuthNonce(nonce);
+        re->set_nonce(nonce.constData(), nonce.size());
+    }
+
     rc.setResponseExtension(re);
     return Response::RespOk;
 }
@@ -3147,6 +3215,39 @@ Response::ResponseCode AbstractServerSocketInterface::cmdReport(const Command_Re
     return Response::RespOk;
 }
 
+Response::ResponseCode
+AbstractServerSocketInterface::cmdSubmitPasswordVerifier(const Command_SubmitPasswordVerifier &cmd,
+                                                         ResponseContainer & /*rc*/)
+{
+    if (authState != PasswordRight) {
+        return Response::RespLoginNeeded;
+    }
+
+    // Limit to the size of the database column (password_sha512 varchar(255)).
+    constexpr int MAX_PASSWORD_VERIFIER_LENGTH = 255;
+    const QString passwordVerifier = QString::fromStdString(cmd.password_verifier());
+    if (passwordVerifier.isEmpty() || passwordVerifier.length() > MAX_PASSWORD_VERIFIER_LENGTH ||
+        PasswordHasher::isLegacyFormat(passwordVerifier)) {
+        return Response::RespContextError;
+    }
+
+    // Reject unparseable or hostile cost parameters before they reach the database.
+    const PasswordVerifier parsedVerifier = PasswordHasher::parsePasswordVerifier(passwordVerifier);
+    if (!parsedVerifier.isValid) {
+        qCWarning(AbstractServerSocketInterfaceLog)
+            << "Rejecting password verifier submission with invalid or insane cost parameters";
+        return Response::RespContextError;
+    }
+
+    if (!sqlInterface->submitPasswordVerifier(QString::fromStdString(userInfo->name()), passwordVerifier)) {
+        return Response::RespContextError;
+    }
+
+    qCDebug(AbstractServerSocketInterfaceLog)
+        << "Password verifier migrated for user" << QString::fromStdString(userInfo->name());
+    return Response::RespOk;
+}
+
 // ADMIN FUNCTIONS.
 // Permission is checked by the calling function.
 

servatrice/src/serversocketinterface.h

@@ -80,6 +80,7 @@ signals:
 protected:
     void logDebugMessage(const QString &message) override;
     bool tooManyRegistrationAttempts(const QString &ipAddress);
+    bool acceptsCredentialFormat(bool passwordNeedsHash, const QString &password) const;
 
     virtual void writeToSocket(QByteArray &data) = 0;
     virtual void flushSocket() = 0;
@@ -145,6 +146,7 @@ private:
     Response::ResponseCode cmdReportDetails(const Command_ReportDetails &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdReportAddComment(const Command_ReportAddComment &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdReplayDownloadByGameId(const Command_ReplayDownloadByGameId &cmd, ResponseContainer &rc);
+    Response::ResponseCode cmdSubmitPasswordVerifier(const Command_SubmitPasswordVerifier &cmd, ResponseContainer &rc);
     Response::ResponseCode
     processExtendedSessionCommand(int cmdType, const SessionCommand &cmd, ResponseContainer &rc) override;
     Response::ResponseCode

tests/password_hash_test.cpp

@@ -36,6 +36,137 @@ TEST(PasswordHashTest, TokenHasExpectedLength)
     const QString token = PasswordHasher::generateActivationToken();
     ASSERT_EQ(token.size(), 16);
 }
+
+TEST(PasswordHashTest, DeriveKeyMatchesKnownVector)
+{
+    // RFC 7914 scrypt test vector, P="password", S="NaCl", N=1024, r=8, p=16
+    const QByteArray expected = QByteArray::fromHex("fdbabe1c9d3472007856e7190d01e9fe7c6ad7cbc8237830e77376634b"
+                                                    "3731622eaf30d92e22a3886ff109279d9830dac727afb94a83ee6d8360cb"
+                                                    "dfa2cc0640");
+    const QByteArray derived = PasswordHasher::deriveKey("password", QByteArray("NaCl"), 1024, 8, 16);
+    ASSERT_EQ(derived.toHex(), expected.toHex());
+}
+
+TEST(PasswordHashTest, PasswordVerifierRoundTrip)
+{
+    const QString stored = PasswordHasher::generatePasswordVerifier("hunter2");
+    ASSERT_FALSE(stored.isEmpty());
+    ASSERT_TRUE(stored.startsWith("$scrypt$"));
+
+    const PasswordVerifier parsed = PasswordHasher::parsePasswordVerifier(stored);
+    ASSERT_TRUE(parsed.isValid);
+    ASSERT_EQ(parsed.format, PasswordFormat::Scrypt);
+    ASSERT_EQ(parsed.n, SCRYPT_N);
+    ASSERT_EQ(parsed.r, SCRYPT_R);
+    ASSERT_EQ(parsed.p, SCRYPT_P);
+    ASSERT_EQ(parsed.salt.size(), SCRYPT_SALT_LENGTH);
+    ASSERT_EQ(parsed.verifier.size(), SCRYPT_VERIFIER_LENGTH);
+}
+
+TEST(PasswordHashTest, PasswordVerifierInvalidInput)
+{
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier("garbage").isValid);
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier("$scrypt$not-an-int$8$1$AAAA$BBBB").isValid);
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier("$scrypt$1024$8$1$AAAA$too-short").isValid);
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier("$pbkdf2-sha512$1000$AAAA$BBBB").isValid);
+}
+
+TEST(PasswordHashTest, LegacyFormatDetection)
+{
+    ASSERT_TRUE(PasswordHasher::isLegacyFormat("salt+hash"));
+    ASSERT_FALSE(PasswordHasher::isLegacyFormat(PasswordHasher::generatePasswordVerifier("password")));
+}
+
+TEST(PasswordHashTest, DeriveKeyDependsOnCostParameters)
+{
+    const QByteArray keyA = PasswordHasher::deriveKey("password", QByteArray("NaCl"), 1024, 8, 16);
+    const QByteArray keyB = PasswordHasher::deriveKey("password", QByteArray("NaCl"), 2048, 8, 16);
+    const QByteArray keyC = PasswordHasher::deriveKey("password", QByteArray("NaCl"), 1024, 8, 1);
+    ASSERT_NE(keyA, keyB);
+    ASSERT_NE(keyA, keyC);
+}
+
+TEST(PasswordHashTest, ComputeResponseIsDeterministic)
+{
+    const QByteArray nonce = QByteArray("a nonce value");
+    const QByteArray key = QByteArray("the verifier bytes");
+    const QByteArray r1 = PasswordHasher::computeResponse(key, nonce);
+    const QByteArray r2 = PasswordHasher::computeResponse(key, nonce);
+    const QByteArray r3 = PasswordHasher::computeResponse(QByteArray("a different key"), nonce);
+    ASSERT_EQ(r1, r2);
+    ASSERT_NE(r1, r3);
+}
+
+TEST(PasswordHashTest, ConstantTimeEquals)
+{
+    ASSERT_TRUE(PasswordHasher::constantTimeEquals(QByteArray("same"), QByteArray("same")));
+    ASSERT_FALSE(PasswordHasher::constantTimeEquals(QByteArray("same"), QByteArray("diff")));
+    ASSERT_FALSE(PasswordHasher::constantTimeEquals(QByteArray("short"), QByteArray("longer")));
+}
+
+TEST(PasswordHashTest, CostParamsAreSane)
+{
+    // Accept the recommended interactive parameters and the RFC 7914 test vector's.
+    ASSERT_TRUE(PasswordHasher::costParamsAreSane(SCRYPT_N, SCRYPT_R, SCRYPT_P));
+    ASSERT_TRUE(PasswordHasher::costParamsAreSane(1024, 8, 16));
+
+    // n must be in [1024, 2**20] and a power of two.
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(512, 8, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1 << 21, 8, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1025, 8, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(0, 8, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(-1024, 8, 1));
+
+    // r in [1, 32], p in [1, 16].
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1024, 0, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1024, 33, 1));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1024, 8, 0));
+    ASSERT_FALSE(PasswordHasher::costParamsAreSane(1024, 8, 17));
+}
+
+TEST(PasswordHashTest, ParsePasswordVerifierRejectsHostileCostParams)
+{
+    // 16 bytes of salt and 64 bytes of verifier, base64 encoded.
+    const QString saltB64 = QLatin1String("c2FsdHNhbHRzYWx0c2FsdA==");
+    const QString verifierB64 = QString(QByteArray(SCRYPT_VERIFIER_LENGTH, '\x42').toBase64());
+
+    ASSERT_TRUE(
+        PasswordHasher::parsePasswordVerifier(QString("$scrypt$1024$8$1$%1$%2").arg(saltB64).arg(verifierB64)).isValid);
+
+    // n not a power of two, below 1024, or above 2**20.
+    ASSERT_FALSE(
+        PasswordHasher::parsePasswordVerifier(QString("$scrypt$1025$8$1$%1$%2").arg(saltB64).arg(verifierB64)).isValid);
+    ASSERT_FALSE(
+        PasswordHasher::parsePasswordVerifier(QString("$scrypt$512$8$1$%1$%2").arg(saltB64).arg(verifierB64)).isValid);
+    ASSERT_FALSE(
+        PasswordHasher::parsePasswordVerifier(QString("$scrypt$1073741824$8$1$%1$%2").arg(saltB64).arg(verifierB64))
+            .isValid);
+
+    // r and p out of range.
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier(QString("$scrypt$1024$33$1$%1$%2").arg(saltB64).arg(verifierB64))
+                     .isValid);
+    ASSERT_FALSE(PasswordHasher::parsePasswordVerifier(QString("$scrypt$1024$8$17$%1$%2").arg(saltB64).arg(verifierB64))
+                     .isValid);
+}
+
+TEST(PasswordHashTest, VerifyPasswordLegacyRow)
+{
+    const QString salt = PasswordHasher::generateRandomSalt();
+    const QString legacyStored = PasswordHasher::computeHash("correct horse", salt);
+    ASSERT_TRUE(PasswordHasher::verifyPassword("correct horse", legacyStored));
+    ASSERT_FALSE(PasswordHasher::verifyPassword("battery staple", legacyStored));
+}
+
+TEST(PasswordHashTest, VerifyPasswordScryptRow)
+{
+    const QString scryptStored = PasswordHasher::generatePasswordVerifier("correct horse");
+    // Regression for the changeUserPassword bug that re-hashed the old password with
+    // a 16-char salt torn out of the "$scrypt$..." string, which could never match.
+    ASSERT_TRUE(PasswordHasher::verifyPassword("correct horse", scryptStored));
+    ASSERT_FALSE(PasswordHasher::verifyPassword("battery staple", scryptStored));
+    ASSERT_FALSE(PasswordHasher::verifyPassword("correct horse", "garbage"));
+}
+
 } // namespace
 
 int main(int argc, char **argv)