Key wrapping and unwrapping in Java JCE

21 Sep 2023

In the field of cryptography, key wrapping is a technique used to provide additional security to encryption keys. It involves encrypting a key using another key known as the wrapping key and storing or transmitting the encrypted key. This ensures that even if the encrypted key is compromised, the original key remains secure.

The Java Cryptography Extension (JCE) provides a number of classes and APIs to perform key wrapping and unwrapping operations. Let’s explore how we can use these functionalities in Java to achieve key wrapping and unwrapping.

Key Wrapping

To perform key wrapping in Java JCE, we need a wrapping key and the key to be wrapped. Here’s an example code snippet to demonstrate key wrapping:

import javax.crypto.Cipher;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
import java.security.spec.RSAPublicKeySpec;

public class KeyWrappingExample {

    public static void main(String[] args) throws Exception {
        // Generate the wrapping key
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        Key wrappingKey = keyPair.getPrivate();

        // Generate the key to be wrapped
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(256);
        Key keyToWrap = keyGenerator.generateKey();

        // Wrap the key
        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");
        cipher.init(Cipher.WRAP_MODE, wrappingKey);
        byte[] wrappedKey = cipher.wrap(keyToWrap);

        // Store or transmit the wrapped key
        System.out.println("Wrapped Key: " + wrappedKey);
    }
}

This code snippet demonstrates key wrapping using an RSA wrapping key and an AES key to be wrapped. The Cipher.WRAP_MODE is used to specify the wrapping operation on the cipher object. The wrapped key can be stored or transmitted securely.

Key Unwrapping

Once we have the wrapped key, we can use the corresponding wrapping key to unwrap it and obtain the original key. Here’s an example code snippet to demonstrate key unwrapping:

import javax.crypto.Cipher;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
import java.security.spec.RSAPublicKeySpec;

public class KeyUnwrappingExample {

    public static void main(String[] args) throws Exception {
        // Generate the wrapping key
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        Key wrappingKey = keyPair.getPrivate();

        // Retrieve the wrapped key (byte array)
        byte[] wrappedKey = getWrappedKey(); // Method to retrieve the wrapped key

        // Unwrap the key
        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");
        cipher.init(Cipher.UNWRAP_MODE, wrappingKey);
        Key unwrappedKey = cipher.unwrap(wrappedKey, "AES", Cipher.SECRET_KEY);

        System.out.println("Unwrapped Key: " + unwrappedKey);
    }

    private static byte[] getWrappedKey() {
        // Method to retrieve the wrapped key (e.g., from storage or network)
        // Return the wrapped key as a byte array
    }
}

In this code snippet, Cipher.UNWRAP_MODE is used to specify the unwrapping operation on the cipher object. The unwrap() method takes the wrapped key, the algorithm of the original key, and the key type as parameters to unwrap and obtain the original key.

Conclusion

Key wrapping and unwrapping are essential techniques in cryptography to enhance the security of encryption keys. In Java JCE, we can utilize the provided classes and APIs to perform key wrapping and unwrapping operations. By following the examples in this article, you can incorporate key wrapping and unwrapping functionality in your Java applications efficiently.

#encryption #keywrapping #java