(Android™) 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 Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

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

    CkCrypt2 crypt = new CkCrypt2();

    // 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 = new CkCert();
    // The LoadFromFile method will automatically detect the format and load it.
    boolean success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer");
    if (success != true) {
        Log.i(TAG, 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..
    CkPrivateKey privKey = new CkPrivateKey();
    String password = "12345678a";
    success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
    if (success != true) {
        Log.i(TAG, 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) {
        Log.i(TAG, crypt.lastErrorText());
        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:
    String originalData = "This is the string to be signed.";
    String opaqueSig = crypt.opaqueSignStringENC(originalData);
    if (crypt.get_LastMethodSuccess() != true) {
        Log.i(TAG, crypt.lastErrorText());
        return;
        }

    Log.i(TAG, 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...

    CkCrypt2 vCrypt = new CkCrypt2();

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

    String extractedData = vCrypt.opaqueVerifyStringENC(opaqueSig);
    if (vCrypt.get_LastMethodSuccess() != true) {
        Log.i(TAG, vCrypt.lastErrorText());
        return;
        }

    Log.i(TAG, "The extracted data: " + extractedData);

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

  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}