bitbox: fix seed command (#4906)

Entropy required to be 64 bytes.

electrum/plugins/digitalbitbox/digitalbitbox.py

@@ -309,7 +309,7 @@ class DigitalBitbox_Client():
     def dbb_generate_wallet(self):
         key = self.stretch_key(self.password)
         filename = ("Electrum-" + time.strftime("%Y-%m-%d-%H-%M-%S") + ".pdf")
-        msg = ('{"seed":{"source": "create", "key": "%s", "filename": "%s", "entropy": "%s"}}' % (key, filename, 'Digital Bitbox Electrum Plugin')).encode('utf8')
+        msg = ('{"seed":{"source": "create", "key": "%s", "filename": "%s", "entropy": "%s"}}' % (key, filename, to_hexstr(os.urandom(32)))).encode('utf8')
         reply = self.hid_send_encrypt(msg)
         if 'error' in reply:
             raise UserFacingException(reply['error']['message'])