(MFC) Create and Verify an Opaque PKCS7/CMS Signature

Demonstrates how 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.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

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

void ChilkatSample(void)
    {
    CkString strOut;

    // 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 PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
    // This example will load the certificate from a .crt and the private key from a .key file

    CkCert cert;
    // The LoadFromFile method will automatically detect the format and load it.
    bool success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer");
    if (success != true) {
        strOut.append(cert.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Our private key is in an encrypted PKCS8 format.
    // If you don't know the format of your key, but you do know it's encrypted,
    // and requires a password, then just call any of the Chilkat methods that load
    // a private key w/ a password argument.  Chilkat will auto-detect the format
    // and load it correctly even if it's not the format indicated by the method name..
    CkPrivateKey privKey;
    const char *password = "12345678a";
    success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
    if (success != true) {
        strOut.append(privKey.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Set properties required for signing.

    // Tell it to use the cert and private key we've loaded.
    success = crypt.SetSigningCert2(cert,privKey);
    if (success != true) {
        strOut.append(crypt.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        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);

    strOut.append(opaqueSig);
    strOut.append("\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) {
        strOut.append(vCrypt.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

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

    const char *extractedData = vCrypt.opaqueVerifyStringENC(opaqueSig);
    if (vCrypt.get_LastMethodSuccess() != true) {
        strOut.append(vCrypt.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    strOut.append("The extracted data: ");
    strOut.append(extractedData);
    strOut.append("\r\n");

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


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }