(C#) A3/A4 Certificate to Create and Verify an Opaque PKCS7/CMS Signature

Demonstrates how to use an A3 or A4 certificate w/ private key on a smartcard or token to create a PKCS7 opaque signature, and also how to verify an opaque signature.

An opaque signature is different than a detached PKCS7 signature in that it contains the original data. Verifying an opaque signature retrieves the original content.

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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();

// A certificate and private key is needed to create a signature.
// Chilkat provides many different ways to load a certificate and private key, such
// as from a smartcards and hardware tokens, PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
// This example will load the default certificate from the smartcard that is currently in
// the smartcard reader.

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

// If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
cert.SmartCardPin = "000000";

bool success = cert.LoadFromSmartcard("");
if (success != true) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

// Tell it to use the cert and private key we've loaded.
success = crypt.SetSigningCert(cert);
if (success != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// Indicate we want the opaque signature in base64 format:
crypt.EncodingMode = "base64";

// Sign the string using the "utf-8" byte representation:
crypt.Charset = "utf-8";

// Create the opaque signature:
string originalData = "This is the string to be signed.";
string opaqueSig = crypt.OpaqueSignStringENC(originalData);
if (crypt.LastMethodSuccess != true) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

Debug.WriteLine(opaqueSig);

// The output looks like this:
// MIIPgQYJKoZIhvcNAQcCoIIPcjCCD24CAQExCzAJBgUrDgMCGgUAMC8GCSqGSIb3DQEHAaAiBCBUaGlzIGlzIHRoZSBzdHJpbmcgdG8gYmUgc...

// ----------------------------------------------------------------------------------------------
// Now let's verify the signature and retrieve the original data.
// We'll use a new Crypt2 object to keep things completely separate...

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

// We only need the certificate to verify a signature (and extract the data from
// an opaque signature).  The public key is always embedded within a certificate.
success = vCrypt.SetVerifyCert(cert);
if (success != true) {
    Debug.WriteLine(vCrypt.LastErrorText);
    return;
}

vCrypt.EncodingMode = "base64";
vCrypt.Charset = "utf-8";

string extractedData = vCrypt.OpaqueVerifyStringENC(opaqueSig);
if (vCrypt.LastMethodSuccess != true) {
    Debug.WriteLine(vCrypt.LastErrorText);
    return;
}

Debug.WriteLine("The extracted data: " + extractedData);

// The output is:
// The extracted data: This is the string to be signed.