An XML file that contains information about all issued CSD (Certificado de Sello Digital) certificates and their current status. SAT (Servicio de Administración Tributaria) maintains the LCO because, during the Timbrado process, the PCCFDI (Proveedor de Certificación de CFDI) must verify that the supplier's signature has been applied with a valid certificate. Although the SAT administration tries to update the LCO every day, it might take one to three days for the LCO to be updated with information on new or revoked certificates. The content of the LCO is confidential, so only PCCFDIs and SAT have access to it.