diff --git a/facho/facho.py b/facho/facho.py
index e4e17e0..8418459 100644
--- a/facho/facho.py
+++ b/facho/facho.py
@@ -118,9 +118,12 @@ class FachoXML:
         # construir las extensiones o adicionar en caso de indicar
         for extension in self.extensions:
             xpath, elements = extension.build(self)
-            for new_element in elements:
-                elem = self.find_or_create_element('/'+ root_tag + xpath)
-                self.builder.append(elem, new_element)
+            if isinstance(elements, str):
+                elem = self.set_element('/'+ root_tag + xpath, elements)
+            else:
+                for new_element in elements:
+                    elem = self.find_or_create_element('/'+ root_tag + xpath)
+                    self.builder.append(elem, new_element)
 
     def fragment(self, xpath, append=False):
         parent = self.find_or_create_element(xpath, append=append)
diff --git a/facho/fe/__init__.py b/facho/fe/__init__.py
index cb73524..2b35d35 100644
--- a/facho/fe/__init__.py
+++ b/facho/fe/__init__.py
@@ -1,4 +1,5 @@
 from .fe import FeXML
 from .fe import NAMESPACES
 from .fe import DianXMLExtensionSigner
+from .fe import DianXMLExtensionSoftwareSecurityCode
 from .fe import DianZIP
diff --git a/facho/fe/client/dian.py b/facho/fe/client/dian.py
index b5951fa..b2281a8 100644
--- a/facho/fe/client/dian.py
+++ b/facho/fe/client/dian.py
@@ -76,7 +76,21 @@ class ConsultaResolucionesFacturacionPeticion(SOAPService):
     def build_response(self, as_dict):
         return ConsultaResolucionesFacturacionRespuesta.fromdict(as_dict)
 
+@dataclass
+class SendBillAsync:
+    fileName: str
+    contentFile: str
 
+    def get_wsdl(self):
+        return 'https://colombia-dian-webservices-input-sbx.azurewebsites.net/WcfDianCustomerServices.svc?wsdl'
+
+    def get_service(self):
+        return 'SendBillAsync'
+
+    def build_response(self, as_dict):
+        return {}
+
+    
 class DianClient:
 
     def __init__(self, user, password):
diff --git a/facho/fe/fe.py b/facho/fe/fe.py
index 085d1e4..5300dfd 100644
--- a/facho/fe/fe.py
+++ b/facho/fe/fe.py
@@ -39,7 +39,23 @@ class FeXML(FachoXML):
         #self.find_or_create_element(self._cn)
 
 
-        
+
+class DianXMLExtensionSoftwareSecurityCode:
+    # RESOLUCION 0001: pagina 535
+    
+    def __init__(self, id_software: str, pin: str, invoice_ident: str):
+        self.id_software = id_software
+        self.pin = pin
+        self.invoice_ident = invoice_ident
+
+    def build(self, fachoxml):
+        dian_path = '/ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sts:DianExtensions/sts:SoftwareSecurityCode'
+        code = str(self.id_software) + str(self.pin) + str(self.invoice_ident)
+        m = hashlib.sha384()
+        m.update(code.encode('utf-8'))
+        return dian_path, m.hexdigest()
+
+    
 class DianXMLExtensionSigner:
     POLICY_ID = 'https://facturaelectronica.dian.gov.co/politicadefirma/v2/politicadefirmav2.pdf'
     POLICY_NAME = 'Dian'
diff --git a/tests/test_fe.py b/tests/test_fe.py
index 939ddd6..956afce 100644
--- a/tests/test_fe.py
+++ b/tests/test_fe.py
@@ -35,3 +35,13 @@ def test_xmlsigned_with_passphrase_build():
     
     assert elem is not None
     #assert elem.findall('ds:SignedInfo', fe.NAMESPACES) is not None
+
+
+def test_dian_extension_software_security_code():
+    security_code = fe.DianXMLExtensionSoftwareSecurityCode('idsoftware', '1234', '1')
+    xml = fe.FeXML('Invoice',
+                   'http://www.dian.gov.co/contratos/facturaelectronica/v1')
+    xml.add_extension(security_code)
+    xml.attach_extensions()
+    content = xml.get_element_text('/fe:Invoice/ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sts:DianExtensions/sts:SoftwareSecurityCode')
+    assert content is not None