Java

About RSA Public/Private Keys

See more RSA Examples

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts. Java

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;

    CkCert cert = new CkCert();

    // Load a digital certificate.
    success = cert.LoadFromFile("digitalCert.cer");
    if (success == false) {
        System.out.println(cert.lastErrorText());
        return;
        }

    // A .cer file does not contain the private key.  It should contain
    // the public key...
    CkPublicKey pubKey = new CkPublicKey();
    cert.GetPublicKey(pubKey);

    // Let's have a look at it (in XML format).
    System.out.println("Public Key from Certificate:");
    System.out.println(pubKey.getXml());

    // An RSA public key consists of a modulus and exponent.

    // An RSA private key includes both the modulus and exponent,
    // as well as other "big" numbers: P, Q, D, etc.

    // Let's load an RSA private key from a DER-encoded file:
    CkPrivateKey privKey = new CkPrivateKey();

    success = privKey.LoadAnyFormatFile("PrivateKey.key","");
    if (success != true) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    // If this private key is the matching half to the public key from
    // the certificate, then the modulus and exponent should
    // be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
    System.out.println("Private Key from DER:");
    System.out.println(privKey.getXml());
  }
}