Warn when sending to already-used Bitcoin addresses

src/interfaces/wallet.h

@@ -125,6 +125,9 @@ class Wallet
     //! Display address on external signer
     virtual bool displayAddress(const CTxDestination& dest) = 0;
 
+    virtual bool checkAddressForUsage(const std::vector<std::string>& addresses) const = 0;
+    virtual bool findAddressUsage(const std::vector<std::string>& addresses, std::function<void(const std::string&, const WalletTx&, uint32_t)> callback) const = 0;
+
     //! Lock coin.
     virtual bool lockCoin(const COutPoint& output, const bool write_to_db) = 0;
 

src/qt/guiconstants.h

@@ -26,6 +26,8 @@ static const bool DEFAULT_SPLASHSCREEN = true;
 
 /* Invalid field background style */
 #define STYLE_INVALID "background:#FF8080"
+/* "Warning" field background style */
+#define STYLE_INCORRECT "background:#FFFF80"
 
 /* Transaction list -- unconfirmed transaction */
 #define COLOR_UNCONFIRMED QColor(128, 128, 128)

src/qt/guiutil.cpp

@@ -81,9 +81,19 @@ void ForceActivation();
 
 namespace GUIUtil {
 
+QString dateStr(const QDate &date)
+{
+    return QLocale::system().toString(date, QLocale::ShortFormat);
+}
+
+QString dateStr(qint64 nTime)
+{
+    return dateStr(QDateTime::fromSecsSinceEpoch(nTime).date());
+}
+
 QString dateTimeStr(const QDateTime &date)
 {
-    return QLocale::system().toString(date.date(), QLocale::ShortFormat) + QString(" ") + date.toString("hh:mm");
+    return dateStr(date.date()) + QString(" ") + date.toString("hh:mm");
 }
 
 QString dateTimeStr(qint64 nTime)

src/qt/guiutil.h

@@ -60,6 +60,8 @@ namespace GUIUtil
     constexpr auto dialog_flags = Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowCloseButtonHint;
 
     // Create human-readable string from date
+    QString dateStr(const QDate &datetime);
+    QString dateStr(qint64 nTime);
     QString dateTimeStr(const QDateTime &datetime);
     QString dateTimeStr(qint64 nTime);
 

src/qt/qvalidatedlineedit.cpp

@@ -15,22 +15,34 @@ QValidatedLineEdit::QValidatedLineEdit(QWidget *parent) :
     connect(this, &QValidatedLineEdit::textChanged, this, &QValidatedLineEdit::markValid);
 }
 
+QValidatedLineEdit::~QValidatedLineEdit()
+{
+    delete m_warning_validator;
+}
+
 void QValidatedLineEdit::setText(const QString& text)
 {
     QLineEdit::setText(text);
     checkValidity();
 }
 
-void QValidatedLineEdit::setValid(bool _valid)
+void QValidatedLineEdit::setValid(bool _valid, bool with_warning)
 {
     if(_valid == this->valid)
     {
-        return;
+        if (with_warning == m_has_warning || !valid) {
+            return;
+        }
     }
 
     if(_valid)
     {
-        setStyleSheet("");
+        m_has_warning = with_warning;
+        if (with_warning) {
+            setStyleSheet("QValidatedLineEdit { " STYLE_INCORRECT "}");
+        } else {
+            setStyleSheet("");
+        }
     }
     else
     {
@@ -84,21 +96,22 @@ void QValidatedLineEdit::setEnabled(bool enabled)
 
 void QValidatedLineEdit::checkValidity()
 {
+    const bool has_warning = checkWarning();
     if (text().isEmpty())
     {
         setValid(true);
     }
     else if (hasAcceptableInput())
     {
-        setValid(true);
+        setValid(true, has_warning);
 
         // Check contents on focus out
         if (checkValidator)
         {
             QString address = text();
             int pos = 0;
             if (checkValidator->validate(address, pos) == QValidator::Acceptable)
-                setValid(true);
+                setValid(true, has_warning);
             else
                 setValid(false);
         }
@@ -128,3 +141,28 @@ bool QValidatedLineEdit::isValid()
 
     return valid;
 }
+
+void QValidatedLineEdit::setWarningValidator(const QValidator *v)
+{
+    delete m_warning_validator;
+    m_warning_validator = v;
+    checkValidity();
+}
+
+bool QValidatedLineEdit::checkWarning() const
+{
+    if (m_warning_validator && !text().isEmpty()) {
+        QString address = text();
+        int pos = 0;
+        if (m_warning_validator->validate(address, pos) != QValidator::Acceptable) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+bool QValidatedLineEdit::hasWarning() const
+{
+    return m_has_warning;
+}

src/qt/qvalidatedlineedit.h

@@ -16,9 +16,12 @@ class QValidatedLineEdit : public QLineEdit
 
 public:
     explicit QValidatedLineEdit(QWidget *parent);
+    ~QValidatedLineEdit();
     void clear();
     void setCheckValidator(const QValidator *v);
     bool isValid();
+    void setWarningValidator(const QValidator *);
+    bool hasWarning() const;
 
 protected:
     void focusInEvent(QFocusEvent *evt) override;
@@ -27,10 +30,12 @@ class QValidatedLineEdit : public QLineEdit
 private:
     bool valid;
     const QValidator *checkValidator;
+    bool m_has_warning{false};
+    const QValidator *m_warning_validator{nullptr};
 
 public Q_SLOTS:
     void setText(const QString&);
-    void setValid(bool valid);
+    void setValid(bool valid, bool with_warning=false);
     void setEnabled(bool enabled);
 
 Q_SIGNALS:
@@ -39,6 +44,7 @@ public Q_SLOTS:
 private Q_SLOTS:
     void markValid();
     void checkValidity();
+    bool checkWarning() const;
 };
 
 #endif // BITCOIN_QT_QVALIDATEDLINEEDIT_H

src/qt/sendcoinsdialog.cpp

@@ -410,9 +410,80 @@ void SendCoinsDialog::sendButtonClicked([[maybe_unused]] bool checked)
     if (!PrepareSendText(question_string, informative_text, detailed_text)) return;
     assert(m_current_transaction);
 
+    bool have_warning = false;
+    for (int i = 0; i < ui->entries->count(); ++i) {
+        SendCoinsEntry *entry = qobject_cast<SendCoinsEntry*>(ui->entries->itemAt(i)->widget());
+        if (entry && entry->hasPaytoWarning()) {
+            have_warning = true;
+            break;
+        }
+    }
+    if (have_warning) {
+        auto recipients = m_current_transaction->getRecipients();
+        struct prior_usage_info_t {
+            CAmount total_amount{0};
+            int num_txs{0};
+            qint64 tx_time_oldest;
+            qint64 tx_time_newest;
+        };
+        QMap<QString, prior_usage_info_t> prior_usage_info;
+        {
+            QStringList addresses;
+            for (const auto& recipient : recipients) {
+                addresses.append(recipient.address);
+            }
+            model->findAddressUsage(addresses, [&prior_usage_info](const QString& address, const interfaces::WalletTx& wtx, uint32_t output_index){
+                auto& info = prior_usage_info[address];
+                info.total_amount += wtx.tx->vout[output_index].nValue;
+                ++info.num_txs;
+                if (info.num_txs == 1 || wtx.time < info.tx_time_oldest) {
+                    info.tx_time_oldest = wtx.time;
+                }
+                if (info.num_txs == 1 || wtx.time > info.tx_time_newest) {
+                    info.tx_time_newest = wtx.time;
+                }
+            });
+        }
+
+        QString reuse_question, reuse_details;
+        if (recipients.size() > 1) {
+            reuse_question = tr("You've already paid some of these addresses.");
+        } else {
+            reuse_question = tr("You've already paid this address.");
+        }
+
+        for (const auto& rcp : recipients) {
+            if (!prior_usage_info.contains(rcp.address)) continue;
+            if (!reuse_details.isEmpty()) reuse_details.append("\n\n");
+            const auto& rcp_prior_usage_info = prior_usage_info.value(rcp.address);
+            const QString label_and_address = rcp.label.isEmpty() ? rcp.address : (QString("'") + rcp.label + "' (" + rcp.address + ")");
+            if (rcp_prior_usage_info.num_txs == 1) {
+                //: %1 is an amount (eg, "1 BTC"); %2 is a Bitcoin address and its label; %3 is a date (eg, "2019-05-08")
+                reuse_details.append(tr("Sent %1 to %2 on %3").arg(BitcoinUnits::formatWithUnit(model->getOptionsModel()->getDisplayUnit(), rcp_prior_usage_info.total_amount), label_and_address, GUIUtil::dateStr(rcp_prior_usage_info.tx_time_newest)));
+            } else {
+                //: %1 is an amount (eg, "1 BTC"); %2 is a Bitcoin address and its label; %3 is the number of transactions; %4 and %5 are dates (eg, "2019-05-08"), earlier first
+                reuse_details.append(tr("Sent %1 to %2 across %3 transactions from %4 through %5").arg(BitcoinUnits::formatWithUnit(model->getOptionsModel()->getDisplayUnit(), rcp_prior_usage_info.total_amount), label_and_address, QString::number(rcp_prior_usage_info.num_txs), GUIUtil::dateStr(rcp_prior_usage_info.tx_time_oldest), GUIUtil::dateStr(rcp_prior_usage_info.tx_time_newest)));
+            }
+        }
+
+        reuse_question.append("<br /><br /><span style='font-size:10pt;'>");
+        reuse_question.append(tr("Bitcoin addresses are intended to only be used once, for a single payment. Sending to the same address again will harm the recipient's security, as well as the privacy of all Bitcoin users!"));
+        reuse_question.append("</span>");
+
+        SendConfirmationDialog confirmation_dialog(tr("Already paid"), reuse_question, "", reuse_details, ADDRESS_REUSE_OVERRIDE_DELAY, /*enable_send=*/true, /*always_show_unsigned=*/false, this);
+        confirmation_dialog.setIcon(QMessageBox::Warning);
+        confirmation_dialog.confirmButtonText = tr("Override");
+        confirmation_dialog.m_yes_button = QMessageBox::Ignore;
+        confirmation_dialog.m_cancel_button = QMessageBox::Ok;
+        if (static_cast<QMessageBox::StandardButton>(confirmation_dialog.exec()) == QMessageBox::Cancel) {
+            fNewRecipientAllowed = true;
+            return;
+        }
+    }
+
     const QString confirmation = tr("Confirm send coins");
     auto confirmationDialog = new SendConfirmationDialog(confirmation, question_string, informative_text, detailed_text, SEND_CONFIRM_DELAY, !model->wallet().privateKeysDisabled(), model->getOptionsModel()->getEnablePSBTControls(), this);
-    confirmationDialog->setAttribute(Qt::WA_DeleteOnClose);
+    confirmationDialog->m_delete_on_close = true;
     // TODO: Replace QDialog::exec() with safer QDialog::show().
     const auto retval = static_cast<QMessageBox::StandardButton>(confirmationDialog->exec());
 
@@ -1045,30 +1116,61 @@ void SendCoinsDialog::coinControlUpdateLabels()
 }
 
 SendConfirmationDialog::SendConfirmationDialog(const QString& title, const QString& text, const QString& informative_text, const QString& detailed_text, int _secDelay, bool enable_send, bool always_show_unsigned, QWidget* parent)
-    : QMessageBox(parent), secDelay(_secDelay), m_enable_send(enable_send)
+    : QMessageBox(parent), secDelay(_secDelay), m_enable_save(always_show_unsigned || !enable_send), m_enable_send(enable_send)
 {
     setIcon(QMessageBox::Question);
     setWindowTitle(title); // On macOS, the window title is ignored (as required by the macOS Guidelines).
     setText(text);
     setInformativeText(informative_text);
     setDetailedText(detailed_text);
-    setStandardButtons(QMessageBox::Yes | QMessageBox::Cancel);
-    if (always_show_unsigned || !enable_send) addButton(QMessageBox::Save);
-    setDefaultButton(QMessageBox::Cancel);
-    yesButton = button(QMessageBox::Yes);
+}
+
+int SendConfirmationDialog::exec()
+{
+    setStandardButtons(m_yes_button | m_cancel_button);
+
+    yesButton = button(m_yes_button);
+    QAbstractButton * const cancel_button_obj = button(m_cancel_button);
+
+    if (m_yes_button != QMessageBox::Yes || m_cancel_button != QMessageBox::Cancel) {
+        // We need to ensure the buttons have Yes/No roles, or they'll get ordered weird
+        // But only do it for customised yes/cancel buttons, so simple code can check results simply too
+        removeButton(cancel_button_obj);
+        addButton(cancel_button_obj, QMessageBox::NoRole);
+        setEscapeButton(cancel_button_obj);
+
+        removeButton(yesButton);
+        addButton(yesButton, QMessageBox::YesRole);
+    }
+
+    if (m_enable_save) addButton(QMessageBox::Save);
+
+    setDefaultButton(m_cancel_button);
+
     if (confirmButtonText.isEmpty()) {
         confirmButtonText = yesButton->text();
     }
     m_psbt_button = button(QMessageBox::Save);
     updateButtons();
-    connect(&countDownTimer, &QTimer::timeout, this, &SendConfirmationDialog::countDown);
-}
 
-int SendConfirmationDialog::exec()
-{
-    updateButtons();
+    connect(&countDownTimer, &QTimer::timeout, this, &SendConfirmationDialog::countDown);
     countDownTimer.start(1s);
-    return QMessageBox::exec();
+
+    QMessageBox::exec();
+
+    int rv;
+    const auto clicked_button = clickedButton();
+    if (clicked_button == m_psbt_button) {
+        rv = QMessageBox::Save;
+    } else if (clicked_button == yesButton) {
+        rv = QMessageBox::Yes;
+    } else {
+        rv = QMessageBox::Cancel;
+    }
+
+    if (m_delete_on_close) delete this;
+
+    return rv;
 }
 
 void SendConfirmationDialog::countDown()

src/qt/sendcoinsdialog.h

@@ -110,12 +110,18 @@ private Q_SLOTS:
 
 
 #define SEND_CONFIRM_DELAY   3
+#define ADDRESS_REUSE_OVERRIDE_DELAY   10
 
 class SendConfirmationDialog : public QMessageBox
 {
     Q_OBJECT
 
 public:
+    bool m_delete_on_close{false};
+    QString confirmButtonText{tr("Send")};
+    QMessageBox::StandardButton m_yes_button{QMessageBox::Yes};
+    QMessageBox::StandardButton m_cancel_button{QMessageBox::Cancel};
+
     SendConfirmationDialog(const QString& title, const QString& text, const QString& informative_text = "", const QString& detailed_text = "", int secDelay = SEND_CONFIRM_DELAY, bool enable_send = true, bool always_show_unsigned = true, QWidget* parent = nullptr);
     int exec() override;
 
@@ -128,7 +134,7 @@ private Q_SLOTS:
     QAbstractButton *m_psbt_button;
     QTimer countDownTimer;
     int secDelay;
-    QString confirmButtonText{tr("Send")};
+    bool m_enable_save;
     bool m_enable_send;
     QString m_psbt_button_text{tr("Create Unsigned")};
 };

src/qt/sendcoinsentry.cpp

@@ -85,6 +85,12 @@ void SendCoinsEntry::setModel(WalletModel *_model)
 {
     this->model = _model;
 
+    if (_model) {
+        ui->payTo->setWarningValidator(new BitcoinAddressUnusedInWalletValidator(*_model));
+    } else {
+        ui->payTo->setWarningValidator(nullptr);
+    }
+
     if (_model && _model->getOptionsModel())
         connect(_model->getOptionsModel(), &OptionsModel::displayUnitChanged, this, &SendCoinsEntry::updateDisplayUnit);
 
@@ -166,6 +172,11 @@ bool SendCoinsEntry::validate(interfaces::Node& node)
     return retval;
 }
 
+bool SendCoinsEntry::hasPaytoWarning() const
+{
+    return ui->payTo->hasWarning();
+}
+
 SendCoinsRecipient SendCoinsEntry::getValue()
 {
     recipient.address = ui->payTo->text();

src/qt/sendcoinsentry.h

@@ -35,6 +35,7 @@ class SendCoinsEntry : public QStackedWidget
 
     void setModel(WalletModel *model);
     bool validate(interfaces::Node& node);
+    bool hasPaytoWarning() const;
     SendCoinsRecipient getValue();
 
     /** Return whether the entry is still empty and unedited */