package io.github.bindon;

import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.Base64;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AesGcmExample {
	public static final int AES_KEY_SIZE = 256;
	public static final int GCM_IV_LENGTH = 12;
	public static final int GCM_TAG_LENGTH = 16;

	public static void main(String[] args) throws Exception {
		// Generate SecretKey
		KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
		keyGenerator.init(AES_KEY_SIZE);
		SecretKey secretKey = keyGenerator.generateKey();
		
		// Generate IV
		byte[] iv = new byte[GCM_IV_LENGTH];
		SecureRandom random = new SecureRandom();
		random.nextBytes(iv);

		// Initialize
		String plaintext = "bindon";
		Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
		SecretKeySpec keySpec = new SecretKeySpec(secretKey.getEncoded(), "AES");
		GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, iv);
		
		// Encrypt
		cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
		byte[] ciphertext = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));

		// Decrypt
		cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
		byte[] decryptedText = cipher.doFinal(ciphertext);
		
		// Print
		System.out.println("Original Text  : " + plaintext);
		System.out.println("Encrypted Text : " + Base64.getUrlEncoder().encodeToString(ciphertext));
		System.out.println("Decrypted Text : " + new String(decryptedText, StandardCharsets.UTF_8));
	}
}