Android™

A3/A4 Certificate to Create and Verify an Opaque PKCS7/CMS Signature

See more Digital Signatures Examples

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.

Android™

// 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);

    boolean success = false;

    //  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 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 = new CkCert();

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

    success = cert.LoadFromSmartcard("");
    if (success != true) {
        Log.i(TAG, cert.lastErrorText());
        return;
        }

    //  Tell it to use the cert and private key we've loaded.
    success = crypt.SetSigningCert(cert);
    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();

    //  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) {
        Log.i(TAG, vCrypt.lastErrorText());
        return;
        }

    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."
  }
}