I am implementing communication with a pay terminal. It uses a soap connection over the internet. I figured out how to do that, it is just a http put with a specific xml, but one of the fields in the xml requires signing the SHA256 of all the other fields with a private certificate and adding it as base64 to the xml.
I also need to verify all the info coming back by checking it with their public certificate.
I have all the certificates and the protocol description.

What I can't figure out is how to do the signing using upp or the actual checking of their signature.

String p7s = HexString(GetP7Signature(data, sign->cert, sign->pkey));