(.NET Core C#) Create CMS Signed File (PDF) with Multiple Signing Certificates

Demonstrates how to sign a file by adding multiple signatures (multiple certificates). This example signs a PDF file to produce an output file that is a CMS signature wrapping the original PDF. (Note: This is different than modifying a PDF by injecting a signature into the PDF file format.)

Note: This example requires Chilkat v9.5.0.83 or greater.

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

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

// ------------ This example requires Chilkat v9.5.0.83 or greater.

Chilkat.Cert cert1 = new Chilkat.Cert();
bool success = cert1.LoadPfxFile("qa_data/pfx/cert_test123.pfx","test123");
if (success != true) {
    Debug.WriteLine(cert1.LastErrorText);
    return;
}

Chilkat.Cert cert2 = new Chilkat.Cert();
success = cert2.LoadPfxFile("qa_data/pfx/test_secret.pfx","secret");
if (success != true) {
    Debug.WriteLine(cert2.LastErrorText);
    return;
}

// ------------ This example requires Chilkat v9.5.0.83 or greater.

// Tell the crypt component to use both certificates for signing. 
// When we create the signature, it will be signed by both certificates.
success = crypt.AddSigningCert(cert1);
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

success = crypt.AddSigningCert(cert2);
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// The CadesEnabled property applies to all methods that create PKCS7 signatures. 
// To create a CAdES-BES signature, set this property equal to true. 
crypt.CadesEnabled = true;

crypt.HashAlgorithm = "sha256";

// We can sign any type of file, creating a .p7s as output.
// The .p7s contains the signature and also embeds the data of the file that is signed.
string inFile = "qa_data/pdf/sample.pdf";
string p7sFile = "qa_output/sample.pdf.p7s";

// Create the CAdES-BES attached signature, which contains the original data.
// Note: Chilkat's function naming is not accurate.  CreateP7M creates a PKCS7 signature where the signed file
// is contained within the signature.  CreateP7S creates a detached PKCS7 signature where the signed file
// is NOT contained within the signature.  We want the data to be contained in the signature, therefore
// we call CreateP7M even though we are naming our output file .p7s.
success = crypt.CreateP7M(inFile,p7sFile);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// Verify the .p7s file and extract the original file from the .p7s. 
string extractedToFilePath = "qa_output/sample.pdf";
success = crypt.VerifyP7M(p7sFile,extractedToFilePath);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

Debug.WriteLine("Success!");