(C# UWP/WinRT) 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 Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// 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 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

Chilkat.Cert cert = new Chilkat.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) {
    Debug.WriteLine(cert.LastErrorText);
    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..
Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();
string password = "12345678a";
success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
if (success != true) {
    Debug.WriteLine(privKey.LastErrorText);
    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) {
    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 = await crypt.OpaqueSignStringENCAsync(originalData);

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.