(Android™) Convert RSA Private Key to Public Key

Demonstrates how to get a public RSA key from a private RSA key.

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);

    CkPrivateKey key = new CkPrivateKey();

    // Step 1: Load the private key from a source.
    // (Chilkat can load private keys from all types of formats, and from in-memory bytes or encoded strings.
    // see the online reference documentation for more options.)
    boolean success = key.LoadPemFile("qa_data/pem/VP_Private.pem");
    if (success != true) {
        Log.i(TAG, key.lastErrorText());
        return;
        }

    // Step 2: Get the public key object from the private key object.
    CkPublicKey pubKey = key.GetPublicKey();
    if (key.get_LastMethodSuccess() != true) {
        Log.i(TAG, key.lastErrorText());
        return;
        }

    // Step 3: Save the public key in a desired format. 
    // (Chilkat can load or save public and private keys in many different formats.  See
    // the online reference documentation for more options.)

    // Saves to a PKCS8 PEM file.
    boolean bPreferPkcs1 = false;
    success = pubKey.SavePemFile(bPreferPkcs1,"qa_data/pem/VP_Public.pem");
    if (pubKey.get_LastMethodSuccess() != true) {
        Log.i(TAG, pubKey.lastErrorText());
        return;
        }

    Log.i(TAG, "Extracted and saved public key from private key.");

  }

  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."
  }
}