(Java) Convert RSA Private Key to Public Key

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

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat Java Downloads Java Libs for Windows, MacOS, Linux, Alpine Linux Java Libs for Android

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = false;

    CkPrivateKey privKey = 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.)
    success = privKey.LoadPemFile("qa_data/pem/VP_Private.pem");
    if (success == false) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    // Step 2: Get the public key object from the private key object.
    CkPublicKey pubKey = new CkPublicKey();
    privKey.ToPublicKey(pubKey);

    // 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() == false) {
        System.out.println(pubKey.lastErrorText());
        return;
        }

    System.out.println("Extracted and saved public key from private key.");
  }
}