Get the S/MIME Signer's Certificate

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Demonstrates the Chilkat Mime.LastSignerCert method, which loads the signer certificate at a zero-based index from the most recent successful verification (or security-unwrapping) into a Cert. The first argument is the signer index and the second is the receiving Cert.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: Verifying tells you the signature is mathematically valid, but you usually also need to know who signed — the subject, the issuer, the validity dates — to decide whether to trust it. This retrieves each signer's certificate after verification so your code can inspect and apply its own trust rules. A message can have multiple signers, so iterate from 0 to NumSignerCerts - 1.

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bool success = false;

Chilkat.Mime mime = new Chilkat.Mime();
success = mime.LoadMimeFile("qa_data/signed.eml");
if (success == false) {
    Debug.WriteLine(mime.LastErrorText);
    return;
}

//  After a successful verification, load each signer's certificate to inspect it.  The 1st argument
//  is the zero-based signer index and the 2nd is a Cert object that receives the certificate.
success = mime.Verify();
if (success != true) {
    Debug.WriteLine(mime.LastErrorText);
    return;
}

int n = mime.NumSignerCerts;
Chilkat.Cert cert = new Chilkat.Cert();
int i;
for (i = 0; i <= n - 1; i++) {
    success = mime.LastSignerCert(i,cert);
    if (success == false) {
        Debug.WriteLine(mime.LastErrorText);
        return;
    }

    Debug.WriteLine("Signer " + Convert.ToString(i) + ": " + cert.SubjectCN + " (issued by " + cert.IssuerCN + ")");
}