(.NET Core C#) Create/Verify XML Signature with External Text Reference

See more XML Digital Signatures Examples

Demonstrates how to create an XML digital signature where the referenced data is external. In this case, the data is a text file located at the following URL: https://www.chilkatsoft.com/helloWorld.txt

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

// This example inserts an XML signature into the following XML:

// <?xml version="1.0" encoding="UTF-8" standalone="no"?>
// <abc>
//   <xyz>
// 	<name>helloWorld.txt</name>
// 	<url>https://www.chilkatsoft.com/helloWorld.txt</url>
//   </xyz>
// </abc>

// Build the above XML to be signed.
Chilkat.Xml xml = new Chilkat.Xml();
xml.Tag = "abc";
xml.UpdateChildContent("xyz|name","helloWorld.txt");
xml.UpdateChildContent("xyz|url","https://www.chilkatsoft.com/helloWorld.txt");

Chilkat.Cert cert = new Chilkat.Cert();

bool success = cert.LoadPfxFile("qa_data/pfx/test_secret.pfx","secret");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Chilkat.XmlDSigGen gen = new Chilkat.XmlDSigGen();

// Indicate the location within the XML the Signature will be inserted.
gen.SigLocation = "abc|xyz";

// Get the content of the text data to be referenced.
Chilkat.Http http = new Chilkat.Http();
Chilkat.StringBuilder sbExternalTxt = new Chilkat.StringBuilder();
success = http.QuickGetSb("https://www.chilkatsoft.com/helloWorld.txt",sbExternalTxt);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

success = gen.AddExternalTextRef("https://www.chilkatsoft.com/helloWorld.txt",sbExternalTxt,"utf-8",false,"sha256","");
if (success == false) {
    Debug.WriteLine(gen.LastErrorText);
    return;
}

// Provide the private key for signing via the certificate, and indicate that
// we want the base64 of the certificate embedded in the KeyInfo.
gen.KeyInfoType = "X509Data";
gen.X509Type = "Certificate";

bool bUsePrivateKey = true;
success = gen.SetX509Cert(cert,bUsePrivateKey);
if (success != true) {
    Debug.WriteLine(gen.LastErrorText);
    return;
}

// Indicate we want an indented signature for readability.
// This can be removed after debugging is finished..
gen.Behaviors = "IndentedSignature";

// Now create and insert the Signature
Chilkat.StringBuilder sbXml = new Chilkat.StringBuilder();
xml.GetXmlSb(sbXml);
success = gen.CreateXmlDSigSb(sbXml);
if (success != true) {
    Debug.WriteLine(gen.LastErrorText);
    return;
}

// Examine the XML with the digital signature inserted
Debug.WriteLine(sbXml.GetAsString());

// Here is the output:

// <?xml version="1.0" encoding="utf-8"?>
// <abc>
//     <xyz>
//         <name>helloWorld.txt</name>
//         <url>https://www.chilkatsoft.com/helloWorld.txt</url>
//     <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
//   <ds:SignedInfo>
//     <ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
//     <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
//     <ds:Reference URI="https://www.chilkatsoft.com/helloWorld.txt">
//       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
//       <ds:DigestValue>f4OxZX/x/FO5LcGBSKHWXfwtSx+j1ncoSt3SABJtkGk=</ds:DigestValue>
//     </ds:Reference>
//   </ds:SignedInfo>
//   <ds:SignatureValue>syFSl...pZDiFQ==</ds:SignatureValue>
//   <ds:KeyInfo>
//     <ds:X509Data>
//       <ds:X509Certificate>MIIHAz...GwnUZWCaDE=</ds:X509Certificate>
//     </ds:X509Data>
//   </ds:KeyInfo>
// </ds:Signature></xyz>
// </abc>

// Let's verify the signature...
Chilkat.XmlDSig verifier = new Chilkat.XmlDSig();
success = verifier.LoadSignatureSb(sbXml);
if (success != true) {
    Debug.WriteLine(verifier.LastErrorText);
    return;
}

// Let's examine the external references, and fetch the data for each..
Chilkat.StringBuilder sbExternalData = new Chilkat.StringBuilder();
int numRefs = verifier.NumReferences;
int i = 0;
while (i < numRefs) {
    bool bExternal = verifier.IsReferenceExternal(i);
    if (bExternal == true) {
        string uri = verifier.ReferenceUri(i);

        // We're assuming the URI is an https:// or http:// URL...
        // Let's also assume we know that the referenced data is text and we want the utf-8 byte representation.
        sbExternalData.Clear();
        success = http.QuickGetSb(uri,sbExternalData);
        if (success == false) {
            Debug.WriteLine(http.LastErrorText);
            return;
        }

        success = verifier.SetRefDataSb(i,sbExternalData,"utf-8");
        if (success == false) {
            Debug.WriteLine(verifier.LastErrorText);
            return;
        }

    }

    i = i + 1;
}

// Now that we have the external data available, we can verify the reference digest(s) and the signature.
bool bVerified = verifier.VerifySignature(true);
if (bVerified != true) {
    Debug.WriteLine(verifier.LastErrorText);
    return;
}

Debug.WriteLine("Signature verified!");