[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/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);