(.NET Core C#) Verify Opaque Signature and Retrieve Signing Certificates

Demonstrates how to verify a PCKS7 opaque digital signature (signed data), extract the original file/data, and then extract the certificate(s) that were used to sign.

Note: This example requires Chilkat v11.0.0 or greater.

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bool success = false;

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

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

// Verify a PKCS7 signed-data (opaque signature) file and extract the original content to a file.
success = crypt.VerifyP7M("qa_data/p7m/opaqueSig.p7","qa_output/originalData.dat");
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// Alternatively, we can do it in memory...
Chilkat.BinData binData = new Chilkat.BinData();
success = binData.LoadFile("qa_data/p7m/opaqueSig.p7");
// Your app should check for success, but we'll skip the check for brevity..

// If verified, the signature is unwrapped and binData is replaced with the original data that was signed.
success = crypt.OpaqueVerifyBd(binData);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// For our testing, we signed some text, so we can get it from the binData..
Debug.WriteLine("Original Data:");
Debug.WriteLine(binData.GetString("utf-8"));

// After any method call that verifies a signature, the crypt object will contain the certificate(s)
// that were used for signing (assuming the X.509 certs were available in the signature, which is typically the case).

// Get each signing certificate, and build the certificate chain for each.
Chilkat.Cert cert = new Chilkat.Cert();
Chilkat.CertChain certChain = new Chilkat.CertChain();
int numCerts = crypt.NumSignerCerts;
int i = 0;
while (i < numCerts) {
    crypt.LastSignerCert(i,cert);
    Debug.WriteLine(cert.SubjectDN);

    success = cert.BuildCertChain(certChain);
    if (success == false) {
        Debug.WriteLine(cert.LastErrorText);
        return;
    }

    i = i + 1;
}