(.NET Core C#) SII Chile - FRMA Signature Computation and Add to XML

Compute the FRMA signature of a <DA> element enclosed inside a <CAF> element of the XML to be signed.

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// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// Also see:  Compute the FRMT Signature and Add to XML

Chilkat.Xml xml = new Chilkat.Xml();

// Load the unsigned XML that contains the following:

// <DTE version="1.0">
//   <Documento ID="F60T33">
//         <TED version="1.0">
//             <DD>
// 		...
//                 <CAF version="1.0">
//                     <DA>
// 			...
//                     </DA>
// 			... The FRMA will be added here ...
//                 </CAF>
//                 ...
//             </DD>
//             ... The FRMT will be added here in another example ...
//         </TED>
//   </Documento>
// </DTE>

bool success = xml.LoadXmlFile("qa_data/xml_dsig/sii_cl/test_0.xml");
if (success == false) {
    Debug.WriteLine("Failed to load initial XML file.");
    return;
}

// Get a reference to the "DA" element
Chilkat.Xml daXml = xml.FindChild("Documento|TED|DD|CAF|DA");
if (xml.LastMethodSuccess == false) {
    Debug.WriteLine("Failed to find DA element");
    return;
}

//  We need to get the "flattened" DA XML where:
//    - No whitespace between elements.
//    - The 5 pre-defined entities are converted.
//    - The text is encoded in the ISO-8859-1 character set (Latin-1), 
Chilkat.StringBuilder sbFlattened = new Chilkat.StringBuilder();
daXml.EmitCompact = true;
daXml.EmitXmlDecl = false;
daXml.GetXmlSb(sbFlattened);

// Compute the SHA-1 message digest of the iso-8859-1 byte representation, 
// and sign it with our RSA private key, getting the result in base64 format.

Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();
success = privKey.LoadAnyFormatFile("qa_data/rsa/rsaPrivKey_pkcs8.pem","");
if (success == false) {
    Debug.WriteLine(privKey.LastErrorText);
    return;
}

Chilkat.Rsa rsa = new Chilkat.Rsa();
rsa.ImportPrivateKeyObj(privKey);

rsa.EncodingMode = "base64";
rsa.Charset = "iso-8859-1";
string sig = rsa.SignStringENC(sbFlattened.GetAsString(),"sha1");

// Add the FRMA signature element to the XML.
xml.UpdateChildContent("Documento|TED|DD|CAF|FRMA",sig);
xml.UpdateAttrAt("Documento|TED|DD|CAF|FRMA",true,"algoritmo","SHA1withRSA");

// See what we have:
xml.EmitCompact = false;
xml.EmitXmlDecl = true;
Debug.WriteLine(xml.GetXml());

xml.SaveXml("qa_data/xml_dsig/sii_cl/test_1.xml");