Merge bitcoin-core/gui#4: UI external signer support (e.g. hardware wallet)

1c4b456e1a0ccf0397d652f8c18201c3224c5c21 gui: send using external signer (Sjors Provoost)
24815c6309431cb0797defaf7add1150bcf4b567 gui: wallet creation detects external signer (Sjors Provoost)
3f845ea2994f53e29abeb3fa158c35f1ee56e7e8 node: add externalSigners to interface (Sjors Provoost)
62ac119f919ae1160ed67af796f24b78025fa8e3 gui: display address on external signer (Sjors Provoost)
450cb40a344605dda3bcc39495c35869580b9fc2 wallet: add displayAddress to interface (Sjors Provoost)
eef8d6452962cd4a8956d9ad268164715365b9ab gui: create wallet with external signer (Sjors Provoost)
6cdbc83e9341d1552faee4ccd8c190babc63e8d1 gui: add external signer path to options dialog (Sjors Provoost)

Pull request description:

  Big picture overview in [this gist](https://gist.github.com/Sjors/29d06728c685e6182828c1ce9b74483d).

  This PR adds GUI support for external signers, based on the since merged bitcoin/bitcoin#16546 (RPC).

  The UX isn't amazing - especially the blocking calls - but it works.

  First we adds a GUI setting for the signer script (e.g. path to HWI):

  <img width="625" alt="Schermafbeelding 2019-08-05 om 19 32 59" src="https://user-images.githubusercontent.com/10217/62483415-e1ff1680-b7b7-11e9-97ca-8d2ce54ca1cb.png">

  Then we add an external signer checkbox to the wallet creation dialog:

  <img width="374" alt="Schermafbeelding 2019-11-07 om 19 17 23" src="https://user-images.githubusercontent.com/10217/68416387-b57ee000-0194-11ea-9730-127d60273008.png">

  It's checked by default if HWI detects a device. It also grabs the name. It then creates a fresh wallet and imports the keys.

  You can verify an address on the device (blocking...):
  <img width="673" alt="Schermafbeelding 2019-08-05 om 19 29 22" src="https://user-images.githubusercontent.com/10217/62483560-43bf8080-b7b8-11e9-9902-8a036116dc4b.png">

  Sending, including coin selection, Just Works(tm) as long the device is present.

  ~External signer support is enabled by default when the GUI is configured and Boost::Process is present.~

  External signer support remains disabled by default, see https://github.com/bitcoin/bitcoin/pull/21935.

ACKs for top commit:
  achow101:
    Code Review ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21
  hebasto:
    ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21, tested on Linux Mint 20.1 (Qt 5.12.8) with HWW `2.0.2-rc.1`.
  promag:
    Tested ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21 but rebased with e033ca1379, with HWI 2.0.2, with Nano S and Nano X.
  meshcollider:
    re-code-review ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21

Tree-SHA512: 3503113c5c69d40adb6ce364d8e7cae23ce82d032a00474ba9aeb6202eb70f496ef4a6bf2e623e5171e524ad31ade7941a4e0e89539c64518aaec74f4562d86b

19 files changed, 284 insertions, 11 deletions

diff --git a/src/interfaces/node.h b/src/interfaces/node.h
index 1dd1e92e2f..35b6160cea 100644
--- a/src/interfaces/node.h
+++ b/src/interfaces/node.h
@@ -6,6 +6,7 @@
 #define BITCOIN_INTERFACES_NODE_H
 
 #include <amount.h>     // For CAmount
+#include <external_signer.h>
 #include <net.h>        // For NodeId
 #include <net_types.h>  // For banmap_t
 #include <netaddress.h> // For Network
@@ -110,6 +111,11 @@ public:
     //! Disconnect node by id.
     virtual bool disconnectById(NodeId id) = 0;
 
+#ifdef ENABLE_EXTERNAL_SIGNER
+    //! List external signers
+    virtual std::vector<ExternalSigner> externalSigners() = 0;
+#endif
+
     //! Get total bytes recv.
     virtual int64_t getTotalBytesRecv() = 0;
 
diff --git a/src/interfaces/wallet.h b/src/interfaces/wallet.h
index 88f93321f9..a0cb2787b7 100644
--- a/src/interfaces/wallet.h
+++ b/src/interfaces/wallet.h
@@ -118,6 +118,9 @@ public:
     //! Save or remove receive request.
     virtual bool setAddressReceiveRequest(const CTxDestination& dest, const std::string& id, const std::string& value) = 0;
 
+    //! Display address on external signer
+    virtual bool displayAddress(const CTxDestination& dest) = 0;
+
     //! Lock coin.
     virtual void lockCoin(const COutPoint& output) = 0;
 
@@ -252,6 +255,9 @@ public:
     // Return whether private keys enabled.
     virtual bool privateKeysDisabled() = 0;
 
+    // Return whether wallet uses an external signer.
+    virtual bool hasExternalSigner() = 0;
+
     // Get default address type.
     virtual OutputType getDefaultAddressType() = 0;
 
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 8befbf5e30..171f15d4fb 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -170,6 +170,16 @@ public:
         }
         return false;
     }
+#ifdef ENABLE_EXTERNAL_SIGNER
+    std::vector<ExternalSigner> externalSigners() override
+    {
+        std::vector<ExternalSigner> signers = {};
+        const std::string command = gArgs.GetArg("-signer", "");
+        if (command == "") return signers;
+        ExternalSigner::Enumerate(command, signers, Params().NetworkIDString());
+        return signers;
+    }
+#endif
     int64_t getTotalBytesRecv() override { return m_context->connman ? m_context->connman->GetTotalBytesRecv() : 0; }
     int64_t getTotalBytesSent() override { return m_context->connman ? m_context->connman->GetTotalBytesSent() : 0; }
     size_t getMempoolSize() override { return m_context->mempool ? m_context->mempool->size() : 0; }
diff --git a/src/qt/createwalletdialog.cpp b/src/qt/createwalletdialog.cpp
index 113bd30a0c..e593697b46 100644
--- a/src/qt/createwalletdialog.cpp
+++ b/src/qt/createwalletdialog.cpp
@@ -6,6 +6,7 @@
 #include <config/bitcoin-config.h>
 #endif
 
+#include <external_signer.h>
 #include <qt/createwalletdialog.h>
 #include <qt/forms/ui_createwalletdialog.h>
 
@@ -27,14 +28,39 @@ CreateWalletDialog::CreateWalletDialog(QWidget* parent) :
     });
 
     connect(ui->encrypt_wallet_checkbox, &QCheckBox::toggled, [this](bool checked) {
-        // Disable the disable_privkeys_checkbox when isEncryptWalletChecked is
+        // Disable the disable_privkeys_checkbox and external_signer_checkbox when isEncryptWalletChecked is
         // set to true, enable it when isEncryptWalletChecked is false.
         ui->disable_privkeys_checkbox->setEnabled(!checked);
+        ui->external_signer_checkbox->setEnabled(!checked);
 
         // When the disable_privkeys_checkbox is disabled, uncheck it.
         if (!ui->disable_privkeys_checkbox->isEnabled()) {
             ui->disable_privkeys_checkbox->setChecked(false);
         }
+
+        // When the external_signer_checkbox box is disabled, uncheck it.
+        if (!ui->external_signer_checkbox->isEnabled()) {
+            ui->external_signer_checkbox->setChecked(false);
+        }
+
+    });
+
+    connect(ui->external_signer_checkbox, &QCheckBox::toggled, [this](bool checked) {
+        ui->encrypt_wallet_checkbox->setEnabled(!checked);
+        ui->blank_wallet_checkbox->setEnabled(!checked);
+        ui->disable_privkeys_checkbox->setEnabled(!checked);
+        ui->descriptor_checkbox->setEnabled(!checked);
+
+        // The external signer checkbox is only enabled when a device is detected.
+        // In that case it is checked by default. Toggling it restores the other
+        // options to their default.
+        ui->descriptor_checkbox->setChecked(checked);
+        ui->encrypt_wallet_checkbox->setChecked(false);
+        ui->disable_privkeys_checkbox->setChecked(checked);
+        // The blank check box is ambiguous. This flag is always true for a
+        // watch-only wallet, even though we immedidately fetch keys from the
+        // external signer.
+        ui->blank_wallet_checkbox->setChecked(checked);
     });
 
     connect(ui->disable_privkeys_checkbox, &QCheckBox::toggled, [this](bool checked) {
@@ -63,11 +89,22 @@ CreateWalletDialog::CreateWalletDialog(QWidget* parent) :
         ui->descriptor_checkbox->setToolTip(tr("Compiled without sqlite support (required for descriptor wallets)"));
         ui->descriptor_checkbox->setEnabled(false);
         ui->descriptor_checkbox->setChecked(false);
+        ui->external_signer_checkbox->setEnabled(false);
+        ui->external_signer_checkbox->setChecked(false);
 #endif
+
 #ifndef USE_BDB
         ui->descriptor_checkbox->setEnabled(false);
         ui->descriptor_checkbox->setChecked(true);
 #endif
+
+#ifndef ENABLE_EXTERNAL_SIGNER
+        //: "External signing" means using devices such as hardware wallets.
+        ui->external_signer_checkbox->setToolTip(tr("Compiled without external signing support (required for external signing)"));
+        ui->external_signer_checkbox->setEnabled(false);
+        ui->external_signer_checkbox->setChecked(false);
+#endif
+
 }
 
 CreateWalletDialog::~CreateWalletDialog()
@@ -75,6 +112,28 @@ CreateWalletDialog::~CreateWalletDialog()
     delete ui;
 }
 
+#ifdef ENABLE_EXTERNAL_SIGNER
+void CreateWalletDialog::setSigners(std::vector<ExternalSigner>& signers)
+{
+    if (!signers.empty()) {
+        ui->external_signer_checkbox->setEnabled(true);
+        ui->external_signer_checkbox->setChecked(true);
+        ui->encrypt_wallet_checkbox->setEnabled(false);
+        ui->encrypt_wallet_checkbox->setChecked(false);
+        // The order matters, because connect() is called when toggling a checkbox:
+        ui->blank_wallet_checkbox->setEnabled(false);
+        ui->blank_wallet_checkbox->setChecked(false);
+        ui->disable_privkeys_checkbox->setEnabled(false);
+        ui->disable_privkeys_checkbox->setChecked(true);
+        const std::string label = signers[0].m_name;
+        ui->wallet_name_line_edit->setText(QString::fromStdString(label));
+        ui->buttonBox->button(QDialogButtonBox::Ok)->setEnabled(true);
+    } else {
+        ui->external_signer_checkbox->setEnabled(false);
+    }
+}
+#endif
+
 QString CreateWalletDialog::walletName() const
 {
     return ui->wallet_name_line_edit->text();
@@ -99,3 +158,8 @@ bool CreateWalletDialog::isDescriptorWalletChecked() const
 {
     return ui->descriptor_checkbox->isChecked();
 }
+
+bool CreateWalletDialog::isExternalSignerChecked() const
+{
+    return ui->external_signer_checkbox->isChecked();
+}
diff --git a/src/qt/createwalletdialog.h b/src/qt/createwalletdialog.h
index 20cce937c8..585b1461f7 100644
--- a/src/qt/createwalletdialog.h
+++ b/src/qt/createwalletdialog.h
@@ -9,6 +9,10 @@
 
 class WalletModel;
 
+#ifdef ENABLE_EXTERNAL_SIGNER
+class ExternalSigner;
+#endif
+
 namespace Ui {
     class CreateWalletDialog;
 }
@@ -23,11 +27,16 @@ public:
     explicit CreateWalletDialog(QWidget* parent);
     virtual ~CreateWalletDialog();
 
+#ifdef ENABLE_EXTERNAL_SIGNER
+    void setSigners(std::vector<ExternalSigner>& signers);
+#endif
+
     QString walletName() const;
     bool isEncryptWalletChecked() const;
     bool isDisablePrivateKeysChecked() const;
     bool isMakeBlankWalletChecked() const;
     bool isDescriptorWalletChecked() const;
+    bool isExternalSignerChecked() const;
 
 private:
     Ui::CreateWalletDialog *ui;
diff --git a/src/qt/forms/createwalletdialog.ui b/src/qt/forms/createwalletdialog.ui
index 881869a46c..b11fb026b0 100644
--- a/src/qt/forms/createwalletdialog.ui
+++ b/src/qt/forms/createwalletdialog.ui
@@ -109,6 +109,16 @@
         </property>
        </widget>
       </item>
+      <item>
+       <widget class="QCheckBox" name="external_signer_checkbox">
+        <property name="toolTip">
+         <string>Use an external signing device such as a hardware wallet. Configure the external signer script in wallet preferences first.</string>
+        </property>
+        <property name="text">
+         <string>External signer</string>
+        </property>
+       </widget>
+      </item>
      </layout>
     </widget>
    </item>
@@ -143,6 +153,7 @@
   <tabstop>disable_privkeys_checkbox</tabstop>
   <tabstop>blank_wallet_checkbox</tabstop>
   <tabstop>descriptor_checkbox</tabstop>
+  <tabstop>external_signer_checkbox</tabstop>
  </tabstops>
  <resources/>
  <connections>
diff --git a/src/qt/forms/optionsdialog.ui b/src/qt/forms/optionsdialog.ui
index f199e8c1a1..bd72328c02 100644
--- a/src/qt/forms/optionsdialog.ui
+++ b/src/qt/forms/optionsdialog.ui
@@ -230,6 +230,36 @@
         </widget>
        </item>
        <item>
+        <widget class="QGroupBox" name="groupBoxHww">
+         <property name="title">
+          <string>External Signer (e.g. hardware wallet)</string>
+         </property>
+         <layout class="QVBoxLayout" name="verticalLayoutHww">
+           <item>
+            <layout class="QHBoxLayout" name="horizontalLayoutHww">
+             <item>
+              <widget class="QLabel" name="externalSignerPathLabel">
+               <property name="text">
+                <string>&amp;External signer script path</string>
+               </property>
+               <property name="buddy">
+                <cstring>externalSignerPath</cstring>
+               </property>
+              </widget>
+             </item>
+             <item>
+              <widget class="QLineEdit" name="externalSignerPath">
+                <property name="toolTip">
+                  <string>Full path to a Bitcoin Core compatible script (e.g. C:\Downloads\hwi.exe or /Users/you/Downloads/hwi.py). Beware: malware can steal your coins!</string>
+                </property>
+              </widget>
+             </item>
+            </layout>
+           </item>
+         </layout>
+        </widget>
+       </item>
+       <item>
         <spacer name="verticalSpacer_Wallet">
          <property name="orientation">
           <enum>Qt::Vertical</enum>
diff --git a/src/qt/forms/receiverequestdialog.ui b/src/qt/forms/receiverequestdialog.ui
index 7d95a8bc90..70a7cf71de 100644
--- a/src/qt/forms/receiverequestdialog.ui
+++ b/src/qt/forms/receiverequestdialog.ui
@@ -255,6 +255,19 @@
       </widget>
      </item>
      <item>
+      <widget class="QPushButton" name="btnVerify">
+       <property name="text">
+        <string>&amp;Verify</string>
+       </property>
+       <property name="toolTip">
+        <string>Verify this address on e.g. a hardware wallet screen</string>
+       </property>
+       <property name="autoDefault">
+        <bool>false</bool>
+       </property>
+      </widget>
+     </item>
+     <item>
       <widget class="QPushButton" name="btnSaveAs">
        <property name="text">
         <string>&amp;Save Image…</string>
diff --git a/src/qt/optionsdialog.cpp b/src/qt/optionsdialog.cpp
index 8a32994e3f..6ad8db4348 100644
--- a/src/qt/optionsdialog.cpp
+++ b/src/qt/optionsdialog.cpp
@@ -199,6 +199,7 @@ void OptionsDialog::setModel(OptionsModel *_model)
     connect(ui->prune, &QCheckBox::clicked, this, &OptionsDialog::togglePruneWarning);
     connect(ui->pruneSize, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
     connect(ui->databaseCache, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
+    connect(ui->externalSignerPath, &QLineEdit::textChanged, [this]{ showRestartWarning(); });
     connect(ui->threadsScriptVerif, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
     /* Wallet */
     connect(ui->spendZeroConfChange, &QCheckBox::clicked, this, &OptionsDialog::showRestartWarning);
@@ -233,6 +234,7 @@ void OptionsDialog::setMapper()
     /* Wallet */
     mapper->addMapping(ui->spendZeroConfChange, OptionsModel::SpendZeroConfChange);
     mapper->addMapping(ui->coinControlFeatures, OptionsModel::CoinControlFeatures);
+    mapper->addMapping(ui->externalSignerPath, OptionsModel::ExternalSignerPath);
 
     /* Network */
     mapper->addMapping(ui->mapPortUpnp, OptionsModel::MapPortUPnP);
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index abdf9e9ae6..24a4e9ee96 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -117,6 +117,13 @@ void OptionsModel::Init(bool resetSettings)
         settings.setValue("bSpendZeroConfChange", true);
     if (!gArgs.SoftSetBoolArg("-spendzeroconfchange", settings.value("bSpendZeroConfChange").toBool()))
         addOverriddenOption("-spendzeroconfchange");
+
+    if (!settings.contains("external_signer_path"))
+        settings.setValue("external_signer_path", "");
+
+    if (!gArgs.SoftSetArg("-signer", settings.value("external_signer_path").toString().toStdString())) {
+        addOverriddenOption("-signer");
+    }
 #endif
 
     // Network
@@ -326,6 +333,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
 #ifdef ENABLE_WALLET
         case SpendZeroConfChange:
             return settings.value("bSpendZeroConfChange");
+        case ExternalSignerPath:
+            return settings.value("external_signer_path");
 #endif
         case DisplayUnit:
             return nDisplayUnit;
@@ -445,6 +454,12 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
                 setRestartRequired(true);
             }
             break;
+        case ExternalSignerPath:
+            if (settings.value("external_signer_path") != value.toString()) {
+                settings.setValue("external_signer_path", value.toString());
+                setRestartRequired(true);
+            }
+            break;
 #endif
         case DisplayUnit:
             setDisplayUnit(value);
diff --git a/src/qt/optionsmodel.h b/src/qt/optionsmodel.h
index 4d012a9b8f..535843e8ba 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -65,6 +65,7 @@ public:
         Prune,                  // bool
         PruneSize,              // int
         DatabaseCache,          // int
+        ExternalSignerPath,     // QString
         SpendZeroConfChange,    // bool
         Listen,                 // bool
         OptionIDRowCount,
diff --git a/src/qt/receiverequestdialog.cpp b/src/qt/receiverequestdialog.cpp
index 78ae5c07da..abe7de8f89 100644
--- a/src/qt/receiverequestdialog.cpp
+++ b/src/qt/receiverequestdialog.cpp
@@ -89,6 +89,12 @@ void ReceiveRequestDialog::setInfo(const SendCoinsRecipient &_info)
         ui->wallet_tag->hide();
         ui->wallet_content->hide();
     }
+
+    ui->btnVerify->setVisible(this->model->wallet().hasExternalSigner());
+
+    connect(ui->btnVerify, &QPushButton::clicked, [this] {
+        model->displayAddress(info.address.toStdString());
+    });
 }
 
 void ReceiveRequestDialog::updateDisplayUnit()
diff --git a/src/qt/sendcoinsdialog.cpp b/src/qt/sendcoinsdialog.cpp
index 160b43324f..e87a2b97bc 100644
--- a/src/qt/sendcoinsdialog.cpp
+++ b/src/qt/sendcoinsdialog.cpp
@@ -199,7 +199,16 @@ void SendCoinsDialog::setModel(WalletModel *_model)
         // set default rbf checkbox state
         ui->optInRBF->setCheckState(Qt::Checked);
 
-        if (model->wallet().privateKeysDisabled()) {
+        if (model->wallet().hasExternalSigner()) {
+            ui->sendButton->setText(tr("Sign on device"));
+            if (gArgs.GetArg("-signer", "") != "") {
+                ui->sendButton->setEnabled(true);
+                ui->sendButton->setToolTip(tr("Connect your hardware wallet first."));
+            } else {
+                ui->sendButton->setEnabled(false);
+                ui->sendButton->setToolTip(tr("Set external signer script path in Options -> Wallet"));
+            }
+        } else if (model->wallet().privateKeysDisabled()) {
             ui->sendButton->setText(tr("Cr&eate Unsigned"));
             ui->sendButton->setToolTip(tr("Creates a Partially Signed Bitcoin Transaction (PSBT) for use with e.g. an offline %1 wallet, or a PSBT-compatible hardware wallet.").arg(PACKAGE_NAME));
         }
@@ -313,14 +322,14 @@ bool SendCoinsDialog::PrepareSendText(QString& question_string, QString& informa
         formatted.append(recipientElement);
     }
 
-    if (model->wallet().privateKeysDisabled()) {
+    if (model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner()) {
         question_string.append(tr("Do you want to draft this transaction?"));
     } else {
         question_string.append(tr("Are you sure you want to send?"));
     }
 
     question_string.append("<br /><span style='font-size:10pt;'>");
-    if (model->wallet().privateKeysDisabled()) {
+    if (model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner()) {
         question_string.append(tr("Please, review your transaction proposal. This will produce a Partially Signed Bitcoin Transaction (PSBT) which you can save or copy and then sign with e.g. an offline %1 wallet, or a PSBT-compatible hardware wallet.").arg(PACKAGE_NAME));
     } else {
         question_string.append(tr("Please, review your transaction."));
@@ -386,8 +395,8 @@ void SendCoinsDialog::sendButtonClicked([[maybe_unused]] bool checked)
     if (!PrepareSendText(question_string, informative_text, detailed_text)) return;
     assert(m_current_transaction);
 
-    const QString confirmation = model->wallet().privateKeysDisabled() ? tr("Confirm transaction proposal") : tr("Confirm send coins");
-    const QString confirmButtonText = model->wallet().privateKeysDisabled() ? tr("Create Unsigned") : tr("Send");
+    const QString confirmation = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner() ? tr("Confirm transaction proposal") : tr("Confirm send coins");
+    const QString confirmButtonText = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner() ? tr("Create Unsigned") : tr("Sign and send");
     SendConfirmationDialog confirmationDialog(confirmation, question_string, informative_text, detailed_text, SEND_CONFIRM_DELAY, confirmButtonText, this);
     confirmationDialog.exec();
     QMessageBox::StandardButton retval = static_cast<QMessageBox::StandardButton>(confirmationDialog.result());
@@ -403,9 +412,58 @@ void SendCoinsDialog::sendButtonClicked([[maybe_unused]] bool checked)
         CMutableTransaction mtx = CMutableTransaction{*(m_current_transaction->getWtx())};
         PartiallySignedTransaction psbtx(mtx);
         bool complete = false;
-        const TransactionError err = model->wallet().fillPSBT(SIGHASH_ALL, false /* sign */, true /* bip32derivs */, psbtx, complete, nullptr);
+        // Always fill without signing first. This prevents an external signer
+        // from being called prematurely and is not expensive.
+        TransactionError err = model->wallet().fillPSBT(SIGHASH_ALL, false /* sign */, true /* bip32derivs */, psbtx, complete, nullptr);
         assert(!complete);
         assert(err == TransactionError::OK);
+        if (model->wallet().hasExternalSigner()) {
+            try {
+                err = model->wallet().fillPSBT(SIGHASH_ALL, true /* sign */, true /* bip32derivs */, psbtx, complete, nullptr);
+            } catch (const std::runtime_error& e) {
+                QMessageBox::critical(nullptr, tr("Sign failed"), e.what());
+                send_failure = true;
+                return;
+            }
+            if (err == TransactionError::EXTERNAL_SIGNER_NOT_FOUND) {
+                QMessageBox::critical(nullptr, tr("External signer not found"), "External signer not found");
+                send_failure = true;
+                return;
+            }
+            if (err == TransactionError::EXTERNAL_SIGNER_FAILED) {
+                QMessageBox::critical(nullptr, tr("External signer failure"), "External signer failure");
+                send_failure = true;
+                return;
+            }
+            if (err != TransactionError::OK) {
+                tfm::format(std::cerr, "Failed to sign PSBT");
+                processSendCoinsReturn(WalletModel::TransactionCreationFailed);
+                send_failure = true;
+                return;
+            }
+            // fillPSBT does not always properly finalize
+            complete = FinalizeAndExtractPSBT(psbtx, mtx);
+        }
+
+        // Broadcast transaction if complete (even with an external signer this
+        // is not always the case, e.g. in a multisig wallet).
+        if (complete) {
+            const CTransactionRef tx = MakeTransactionRef(mtx);
+            m_current_transaction->setWtx(tx);
+            WalletModel::SendCoinsReturn sendStatus = model->sendCoins(*m_current_transaction);
+            // process sendStatus and on error generate message shown to user
+            processSendCoinsReturn(sendStatus);
+
+            if (sendStatus.status == WalletModel::OK) {
+                Q_EMIT coinsSent(m_current_transaction->getWtx()->GetHash());
+            } else {
+                send_failure = true;
+            }
+            return;
+        }
+
+        // Copy PSBT to clipboard and offer to save
+        assert(!complete);
         // Serialize the PSBT
         CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
         ssTx << psbtx;
@@ -447,7 +505,7 @@ void SendCoinsDialog::sendButtonClicked([[maybe_unused]] bool checked)
             break;
         default:
             assert(false);
-        }
+        } // msgBox.exec()
     } else {
         // now send the prepared transaction
         WalletModel::SendCoinsReturn sendStatus = model->sendCoins(*m_current_transaction);
@@ -614,7 +672,9 @@ void SendCoinsDialog::setBalance(const interfaces::WalletBalances& balances)
     if(model && model->getOptionsModel())
     {
         CAmount balance = balances.balance;
-        if (model->wallet().privateKeysDisabled()) {
+        if (model->wallet().hasExternalSigner()) {
+            ui->labelBalanceName->setText(tr("External balance:"));
+        } else if (model->wallet().privateKeysDisabled()) {
             balance = balances.watch_only_balance;
             ui->labelBalanceName->setText(tr("Watch-only balance:"));
         }
@@ -698,7 +758,7 @@ void SendCoinsDialog::on_buttonMinimizeFee_clicked()
 void SendCoinsDialog::useAvailableBalance(SendCoinsEntry* entry)
 {
     // Include watch-only for wallets without private key
-    m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled();
+    m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner();
 
     // Calculate available amount to send.
     CAmount amount = model->wallet().getAvailableBalance(*m_coin_control);
@@ -753,7 +813,7 @@ void SendCoinsDialog::updateCoinControlState()
     m_coin_control->m_confirm_target = getConfTargetForIndex(ui->confTargetSelector->currentIndex());
     m_coin_control->m_signal_bip125_rbf = ui->optInRBF->isChecked();
     // Include watch-only for wallets without private key
-    m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled();
+    m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner();
 }
 
 void SendCoinsDialog::updateNumberOfBlocks(int count, const QDateTime& blockDate, double nVerificationProgress, bool headers, SynchronizationState sync_state) {
diff --git a/src/qt/walletcontroller.cpp b/src/qt/walletcontroller.cpp
index aa26a01541..7e5790fd87 100644
--- a/src/qt/walletcontroller.cpp
+++ b/src/qt/walletcontroller.cpp
@@ -263,6 +263,9 @@ void CreateWalletActivity::createWallet()
     if (m_create_wallet_dialog->isDescriptorWalletChecked()) {
         flags |= WALLET_FLAG_DESCRIPTORS;
     }
+    if (m_create_wallet_dialog->isExternalSignerChecked()) {
+        flags |= WALLET_FLAG_EXTERNAL_SIGNER;
+    }
 
     QTimer::singleShot(500, worker(), [this, name, flags] {
         std::unique_ptr<interfaces::Wallet> wallet = node().walletClient().createWallet(name, m_passphrase, flags, m_error_message, m_warning_message);
@@ -291,6 +294,17 @@ void CreateWalletActivity::finish()
 void CreateWalletActivity::create()
 {
     m_create_wallet_dialog = new CreateWalletDialog(m_parent_widget);
+
+#ifdef ENABLE_EXTERNAL_SIGNER
+    std::vector<ExternalSigner> signers;
+    try {
+        signers = node().externalSigners();
+    } catch (const std::runtime_error& e) {
+        QMessageBox::critical(nullptr, tr("Can't list signers"), e.what());
+    }
+    m_create_wallet_dialog->setSigners(signers);
+#endif
+
     m_create_wallet_dialog->setWindowModality(Qt::ApplicationModal);
     m_create_wallet_dialog->show();
 
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 7c58b8afd2..e32b7c2807 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -552,6 +552,18 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
     return true;
 }
 
+bool WalletModel::displayAddress(std::string sAddress)
+{
+    CTxDestination dest = DecodeDestination(sAddress);
+    bool res = false;
+    try {
+        res = m_wallet->displayAddress(dest);
+    } catch (const std::runtime_error& e) {
+        QMessageBox::critical(nullptr, tr("Can't display address"), e.what());
+    }
+    return res;
+}
+
 bool WalletModel::isWalletEnabled()
 {
    return !gArgs.GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET);
diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index b2ce5d69fb..47a21bcfcf 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -136,6 +136,7 @@ public:
     UnlockContext requestUnlock();
 
     bool bumpFee(uint256 hash, uint256& new_hash);
+    bool displayAddress(std::string sAddress);
 
     static bool isWalletEnabled();
 
diff --git a/src/qt/walletmodeltransaction.cpp b/src/qt/walletmodeltransaction.cpp
index 25172e774c..d185ddb7e8 100644
--- a/src/qt/walletmodeltransaction.cpp
+++ b/src/qt/walletmodeltransaction.cpp
@@ -26,6 +26,11 @@ CTransactionRef& WalletModelTransaction::getWtx()
     return wtx;
 }
 
+void WalletModelTransaction::setWtx(const CTransactionRef& newTx)
+{
+    wtx = newTx;
+}
+
 unsigned int WalletModelTransaction::getTransactionSize()
 {
     return wtx ? GetVirtualTransactionSize(*wtx) : 0;
diff --git a/src/qt/walletmodeltransaction.h b/src/qt/walletmodeltransaction.h
index f9a95362c8..120d240d91 100644
--- a/src/qt/walletmodeltransaction.h
+++ b/src/qt/walletmodeltransaction.h
@@ -27,6 +27,8 @@ public:
     QList<SendCoinsRecipient> getRecipients() const;
 
     CTransactionRef& getWtx();
+    void setWtx(const CTransactionRef&);
+
     unsigned int getTransactionSize();
 
     void setTransactionFee(const CAmount& newFee);
diff --git a/src/wallet/interfaces.cpp b/src/wallet/interfaces.cpp
index aca52964ee..ee92316b89 100644
--- a/src/wallet/interfaces.cpp
+++ b/src/wallet/interfaces.cpp
@@ -206,6 +206,11 @@ public:
         WalletBatch batch{m_wallet->GetDatabase()};
         return m_wallet->SetAddressReceiveRequest(batch, dest, id, value);
     }
+    bool displayAddress(const CTxDestination& dest) override
+    {
+        LOCK(m_wallet->cs_wallet);
+        return m_wallet->DisplayAddress(dest);
+    }
     void lockCoin(const COutPoint& output) override
     {
         LOCK(m_wallet->cs_wallet);
@@ -446,6 +451,7 @@ public:
     unsigned int getConfirmTarget() override { return m_wallet->m_confirm_target; }
     bool hdEnabled() override { return m_wallet->IsHDEnabled(); }
     bool canGetAddresses() override { return m_wallet->CanGetAddresses(); }
+    bool hasExternalSigner() override { return m_wallet->IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER); }
     bool privateKeysDisabled() override { return m_wallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS); }
     OutputType getDefaultAddressType() override { return m_wallet->m_default_address_type; }
     CAmount getDefaultMaxTxFee() override { return m_wallet->m_default_max_tx_fee; }