Satochip plugin: use BIP39 by default & improve user interface

Seed generation: use BIP39 by default for better compatibility:
* Most (all?) hardware wallets use BIP39 seeds in combination with BIP43-style derivation paths (like m / purpose' / coin_type' / account' / change / address_index)
* Electrum uses BIP43 derivation paths for all hardware wallets, AND for BIP39 seeds imported in software wallets
* Electrum seeds (not BIP39) use seed versioning instead of purpose derivation path.
* Software wallets with Electrum seeds use "m / change / address_index" derivation paths

User interface improvements:
* 2FA config is removed from initial setup as it confuses some users
* Instead, 2FA can be activated from the option menu (clicking on the Satochip logo on the lower right corner

Other minor corrections:
* PIN can have a maximum length of 16, not 64

electroncash_plugins/satochip/qt.py

@@ -1,21 +1,25 @@
 from electroncash.i18n import _
 from electroncash.util import print_error
-from electroncash.plugins import run_hook
 from electroncash_gui.qt.util import EnterButton, Buttons, CloseButton, OkButton, CancelButton, WindowModalDialog, WWLabel 
+from electroncash_gui.qt.qrcodewidget import QRCodeWidget, QRDialog
 
 from PyQt5.QtCore import Qt, pyqtSignal
 from PyQt5.QtWidgets import QPushButton, QLabel, QVBoxLayout, QWidget, QGridLayout, QLineEdit, QCheckBox
 from functools import partial
+from os import urandom
+
 
-from ..hw_wallet.qt import QtHandlerBase, QtPluginBase
 #satochip
 from .satochip import SatochipPlugin
+from ..hw_wallet.qt import QtHandlerBase, QtPluginBase
 
 #pysatochip 
 from pysatochip.CardConnector import CardConnector
 from pysatochip.Satochip2FA import Satochip2FA                                       
 from pysatochip.version import SATOCHIP_PROTOCOL_MAJOR_VERSION, SATOCHIP_PROTOCOL_MINOR_VERSION
 
+MSG_USE_2FA= _("Do you want to use 2-Factor-Authentication (2FA)?\n\nWith 2FA, any transaction must be confirmed on a second device such as your smartphone. First you have to install the Satochip-2FA android app on google play. Then you have to pair your 2FA device with your Satochip by scanning the qr-code on the next screen. \n\nWARNING: be sure to backup a copy of the qr-code in a safe place, in case you have to reinstall the app!")
+
 class Plugin(SatochipPlugin, QtPluginBase):
     # icon_unpaired = "satochip_unpaired.png"
     # icon_paired = "satochip.png"
@@ -48,9 +52,16 @@ def settings_dialog(self, window):
 
     def show_settings_dialog(self, window, keystore):
         # When they click on the icon for Satochip we come here.
-        device_id = self.choose_device(window, keystore)
-        if device_id:
-            SatochipSettingsDialog(window, self, keystore, device_id).exec_()
+        # device_id = self.choose_device(window, keystore)
+        # if device_id:
+            # SatochipSettingsDialog(window, self, keystore, device_id).exec_()
+        def connect():
+            device_id = self.choose_device(window, keystore)
+            return device_id
+        def show_dialog(device_id):
+            if device_id:
+                SatochipSettingsDialog(window, self, keystore, device_id).exec_()
+        keystore.thread.add(connect, on_success=show_dialog)
 
 class Satochip_Handler(QtHandlerBase):
 
@@ -92,7 +103,7 @@ def connect_and_doit():
 <br><a href="https://satochip.io">satochip.io</a>''')
         title.setTextInteractionFlags(Qt.LinksAccessibleByMouse)
 
-        grid.addWidget(title , 0,0, 1,2, Qt.AlignHCenter)
+        grid.addWidget(title, 0, 0, 1, 2, Qt.AlignHCenter)
         y = 3
 
         rows = [
@@ -118,17 +129,34 @@ def _change_pin():
             thread.add(connect_and_doit, on_success=self.change_pin)
         pin_btn.clicked.connect(_change_pin)
 
-        seed_btn = QPushButton('reset seed')
+        seed_btn = QPushButton('Reset seed')
         def _reset_seed():
             thread.add(connect_and_doit, on_success=self.reset_seed)
             thread.add(connect_and_doit, on_success=self.show_values)
         seed_btn.clicked.connect(_reset_seed)
 
+        set_2FA_btn = QPushButton('Enable 2FA')
+        def _set_2FA():
+            thread.add(connect_and_doit, on_success=self.set_2FA)
+            thread.add(connect_and_doit, on_success=self.show_values)
+        set_2FA_btn.clicked.connect(_set_2FA)
+
+        reset_2FA_btn = QPushButton('Disable 2FA')
+        def _reset_2FA():
+            thread.add(connect_and_doit, on_success=self.reset_2FA)
+            thread.add(connect_and_doit, on_success=self.show_values)
+        reset_2FA_btn.clicked.connect(_reset_2FA)
+
         y += 3
-        grid.addWidget(pin_btn, y, 0)
-        grid.addWidget(seed_btn, y, 1)
-        y += 5
-        grid.addWidget(CloseButton(self), y, 1)
+        grid.addWidget(pin_btn, y, 0, 1, 2, Qt.AlignHCenter)
+        y += 2
+        grid.addWidget(seed_btn, y, 0, 1, 2, Qt.AlignHCenter)
+        y += 2
+        grid.addWidget(set_2FA_btn, y, 0, 1, 2, Qt.AlignHCenter)
+        y += 2
+        grid.addWidget(reset_2FA_btn, y, 0, 1, 2, Qt.AlignHCenter)
+        y += 2
+        grid.addWidget(CloseButton(self), y, 0, 1, 2, Qt.AlignHCenter)
 
         dialog_vbox = QVBoxLayout(self)
         dialog_vbox.addWidget(body)
@@ -209,7 +237,7 @@ def reset_seed(self, client):
             _("Please be sure that your wallet is empty and that you have a backup of the seed as a precaution.\n\n"),
             _("To proceed, enter the PIN for your Satochip:")
         ])
-        (password, reset_2FA)= self.reset_seed_dialog(msg)
+        password = self.reset_seed_dialog(msg)
         if (password is None):
             return
         pin = password.encode('utf8')
@@ -254,11 +282,59 @@ def reset_seed(self, client):
             msg= _("Seed reset successfully!\nYou should close this wallet and launch the wizard to generate a new wallet.")
             client.handler.show_message(msg)
             #to do: close client?
+        elif (sw1==0x9c and sw2==0x0b):
+            msg= _(f"Failed to reset seed: request rejected by 2FA device (error code: {hex(256*sw1+sw2)})")
+            client.handler.show_message(msg)
+            #to do: close client?
         else:
-            msg= _(f"Failed to reset seed with error code: {hex(sw1)}{hex(sw2)}")
+            msg= _(f"Failed to reset seed with error code: {hex(256*sw1+sw2)}")
             client.handler.show_error(msg)
 
-        if reset_2FA and client.cc.needs_2FA:
+    def reset_seed_dialog(self, msg):
+        print_error("In reset_seed_dialog")
+        parent = self.top_level_window()
+        d = WindowModalDialog(parent, _("Enter PIN"))
+        pw = QLineEdit()
+        pw.setEchoMode(2)
+        pw.setMinimumWidth(200)
+
+        vbox = QVBoxLayout()
+        vbox.addWidget(WWLabel(msg))
+        vbox.addWidget(pw)
+        vbox.addLayout(Buttons(CancelButton(d), OkButton(d)))
+        d.setLayout(vbox)
+
+        passphrase = pw.text() if d.exec_() else None
+        return passphrase 
+
+    def set_2FA(self, client):
+        if not client.cc.needs_2FA:
+            use_2FA=client.handler.yes_no_question(MSG_USE_2FA)
+            if (use_2FA):
+                secret_2FA= urandom(20)
+                secret_2FA_hex=secret_2FA.hex()
+                # the secret must be shared with the second factor app (eg on a smartphone)
+                try:
+                    d = QRDialog(secret_2FA_hex, None, "Scan secret 2FA and save a copy", True)
+                    d.exec_()
+                except Exception as e:
+                    print_error("SatochipPlugin: setup 2FA error: "+str(e))
+                    return
+                # further communications will require an id and an encryption key (for privacy). 
+                # Both are derived from the secret_2FA using a one-way function inside the Satochip
+                amount_limit= 0 # i.e. always use 
+                (response, sw1, sw2)=client.cc.card_set_2FA_key(secret_2FA, amount_limit)
+                if sw1!=0x90 or sw2!=0x00:                 
+                    print_error(f"Unable to set 2FA with error code:= {hex(256*sw1+sw2)}")#debugSatochip
+                    raise RuntimeError(f'Unable to setup 2FA with error code: {hex(256*sw1+sw2)}')
+                else:
+                    client.handler.show_message("2FA enabled successfully!") 
+        else:
+            msg= _(f"2FA is already enabled!")
+            client.handler.show_error(msg)    
+
+    def reset_2FA(self, client):
+        if client.cc.needs_2FA: 
             # challenge based on ID_2FA
             # format & encrypt msg
             import json
@@ -278,7 +354,7 @@ def reset_seed(self, client):
             try:
                 reply_encrypt= d['reply_encrypt']
             except Exception as e:
-                self.give_error("No response received from 2FA.\nPlease ensure that the Satochip-2FA plugin is enabled in Tools>Optional Features", True)
+                self.give_error("No response received from 2FA!", True)
             reply_decrypt= client.cc.card_crypt_transaction_2FA(reply_encrypt, False)
             print_error("challenge:response= "+ reply_decrypt)
             reply_decrypt= reply_decrypt.split(":")
@@ -291,30 +367,15 @@ def reset_seed(self, client):
                 msg= _("2FA reset successfully!")
                 client.cc.needs_2FA= False
                 client.handler.show_message(msg)
+            elif (sw1==0x9c and sw2==0x17):
+                msg= _(f"Failed to reset 2FA: \nyou must reset the seed first (error code {hex(256*sw1+sw2)})")
+                client.handler.show_error(msg)    
+            elif (sw1==0x9c and sw2==0x0b):
+                msg= _(f"Failed to reset 2FA: \nrequest rejected by 2FA device (error code: {hex(256*sw1+sw2)})")
+                client.handler.show_message(msg)
             else:
-                msg= _(f"Failed to reset 2FA with error code: {hex(sw1)}{hex(sw2)}")
-                client.handler.show_error(msg)
-
-    def reset_seed_dialog(self, msg):
-        print_error("In reset_seed_dialog")
-        parent = self.top_level_window()
-        d = WindowModalDialog(parent, _("Enter PIN"))
-        pw = QLineEdit()
-        pw.setEchoMode(2)
-        pw.setMinimumWidth(200)
-
-        cb_reset_2FA = QCheckBox(_('Also reset 2FA'))
-
-        vbox = QVBoxLayout()
-        vbox.addWidget(WWLabel(msg))
-        vbox.addWidget(pw)
-        vbox.addWidget(cb_reset_2FA)
-        vbox.addLayout(Buttons(CancelButton(d), OkButton(d)))
-        d.setLayout(vbox)
-
-        passphrase = pw.text() if d.exec_() else None
-
-        reset_2FA= cb_reset_2FA.isChecked()
-        return (passphrase, reset_2FA)
-
-
+                msg= _(f"Failed to reset 2FA with error code: {hex(256*sw1+sw2)}")
+                client.handler.show_error(msg)    
+        else:
+            msg= _(f"2FA is already disabled!")
+            client.handler.show_error(msg)