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import javax.crypto.Cipher;
import java.security.*;

public class RSAOEAPExample {

    public static void main(String[] args) throws Exception {
        // Generate RSA key pair
        KeyPair keyPair = generateRSAKeyPair();

        // Message to be encrypted
        String originalMessage = "Hello, RSA-OEAP!";

        // Encrypt the message
        byte[] encryptedMessage = encrypt(originalMessage, keyPair.getPublic());

        // Decrypt the message
        String decryptedMessage = decrypt(encryptedMessage, keyPair.getPrivate());

        // Display the results
        System.out.println("Original Message: " + originalMessage);
        System.out.println("Encrypted Message: " + bytesToHex(encryptedMessage));
        System.out.println("Decrypted Message: " + decryptedMessage);
    }

    // Generate RSA key pair
    public static KeyPair generateRSAKeyPair() throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048); // You can adjust the key size as needed
        return keyPairGenerator.generateKeyPair();
    }

    // Encrypt using RSA-OEAP
    public static byte[] encrypt(String message, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(message.getBytes());
    }

    // Decrypt using RSA-OEAP
    public static String decrypt(byte[] encryptedMessage, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptedBytes = cipher.doFinal(encryptedMessage);
        return new String(decryptedBytes);
    }

    // Convert bytes to hexadecimal string
    private static String bytesToHex(byte[] bytes) {
        StringBuilder hexString = new StringBuilder();
        for (byte b : bytes) {
            hexString.append(String.format("%02X", b));
        }
        return hexString.toString();
    }
}
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