(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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#include <CkCrypt2.h>
#include <CkCert.h>

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

    CkCrypt2 crypt;

    // 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.

    CkCert cert;

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

    bool success = cert.LoadFromSmartcard("");
    if (success != true) {
        std::cout << cert.lastErrorText() << "\r\n";
        return;
    }

    // Tell it to use the cert and private key we've loaded.
    success = crypt.SetSigningCert(cert);
    if (success != true) {
        std::cout << crypt.lastErrorText() << "\r\n";
        return;
    }

    // Indicate we want the opaque signature in base64 format:
    crypt.put_EncodingMode("base64");

    // Sign the string using the "utf-8" byte representation:
    crypt.put_Charset("utf-8");

    // Create the opaque signature:
    const char *originalData = "This is the string to be signed.";
    const char *opaqueSig = crypt.opaqueSignStringENC(originalData);
    if (crypt.get_LastMethodSuccess() != true) {
        std::cout << crypt.lastErrorText() << "\r\n";
        return;
    }

    std::cout << opaqueSig << "\r\n";

    // 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...

    CkCrypt2 vCrypt;

    // 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) {
        std::cout << vCrypt.lastErrorText() << "\r\n";
        return;
    }

    vCrypt.put_EncodingMode("base64");
    vCrypt.put_Charset("utf-8");

    const char *extractedData = vCrypt.opaqueVerifyStringENC(opaqueSig);
    if (vCrypt.get_LastMethodSuccess() != true) {
        std::cout << vCrypt.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "The extracted data: " << extractedData << "\r\n";

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