Java Requires Chilkat v11.0.0+

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. Chilkat2 Java

import com.chilkatsoft.chilkat2.Cert;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.PrivateKey;
import com.chilkatsoft.chilkat2.PublicKey;

public class ChilkatExample {

    public static void main(String[] args) {
        Cert cert = new Cert();

        // Load a digital certificate.
        try {
            cert.loadFromFile("digitalCert.cer");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // A .cer file does not contain the private key.  It should contain
        // the public key...
        PublicKey pubKey = new PublicKey();
        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:
        PrivateKey privKey = new PrivateKey();

        try {
            privKey.loadAnyFormatFile("PrivateKey.key", "");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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());
    }
}