This implementation is based on https://github.com/artemkunich/goxades - refer there for the original code. The code here has been heavily modified to suit the requirements for Electronic Signatures in Ecuador, especially for the purpose of signing invoices in a format appropriate for SRI. In most cases, the code works the same as the original project if you don't use any extra options. However, by using the new options you can make the project generate output appropriate for SRI, including identifiers with random numbers in them and other necessary components.