Aes256Util.java - AES/GCM/NoPadding

 

encryptByRandom 은 iv가 random하게 생성되어서 같은 값을 암호화 하더라도 항상 다르게 나옵니다.
encryptByFix 는 iv가 key를 참조해 생성되어서 항상 같은 값으로 암호화 됩니다.

 

 decrypt는 앞의 16자리를 iv로 참조해서 복호화하므로 encrypt 방법과 무관하게 복호화 됩니다.

	import java.security.InvalidAlgorithmParameterException;
	import java.security.InvalidKeyException;
	import java.security.NoSuchAlgorithmException;
	import java.security.SecureRandom;
	import java.util.Arrays;
	import java.util.Base64;
	import javax.crypto.BadPaddingException;
	import javax.crypto.Cipher;
	import javax.crypto.IllegalBlockSizeException;
	import javax.crypto.NoSuchPaddingException;
	import javax.crypto.spec.GCMParameterSpec;
	import javax.crypto.spec.SecretKeySpec;
	public class Aes256Util {
	public static final int GCM_IV_LENGTH = 16;
	public static final int GCM_TAG_LENGTH = 128;
	public static String encryptByRandom(String plaintext, byte[] key)
	throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException,
	IllegalBlockSizeException, BadPaddingException {
	if (plaintext == null) {
	return null;
	}
	SecureRandom random = new SecureRandom();
	byte[] iv = new byte[GCM_IV_LENGTH];
	random.nextBytes(iv);
	SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
	Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
	GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);
	cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
	byte[] cipherText = cipher.doFinal(plaintext.getBytes());
	return new String(Base64.getEncoder().encode(concatenate(iv, cipherText)));
	}
	public static String encryptByFix(String plaintext, byte[] key)
	throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException,
	IllegalBlockSizeException, BadPaddingException {
	if (plaintext == null) {
	return null;
	}
	byte[] iv = Arrays.copyOfRange(key, 0, GCM_IV_LENGTH);
	SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
	Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
	GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);
	cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
	byte[] cipherText = cipher.doFinal(plaintext.getBytes());
	return new String(Base64.getEncoder().encode(concatenate(iv, cipherText)));
	}
	public static String decrypt(String str, byte[] key) throws NoSuchAlgorithmException, NoSuchPaddingException,
	InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException {
	if (str == null) {
	return null;
	}
	byte[] ciphertext = Base64.getDecoder().decode(str.getBytes());
	byte[] iv = Arrays.copyOfRange(ciphertext, 0, GCM_IV_LENGTH);
	byte[] cipherText = Arrays.copyOfRange(ciphertext, GCM_IV_LENGTH, ciphertext.length);
	SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
	Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
	GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);
	cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
	return new String(cipher.doFinal(cipherText));
	}
	private static byte[] concatenate(byte[] firstArray, byte[] secondArray) {
	byte[] result = Arrays.copyOf(firstArray, firstArray.length + secondArray.length);
	System.arraycopy(secondArray, 0, result, firstArray.length, secondArray.length);
	return result;
	}
	}

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	public class Aes256UtilTest {
	public static void main(String[] args) throws Exception {
	byte[] key = "92c42d9dk49dhj3480gh280h08sb80f0".getBytes();
	for (int i = 0; i < 60; i++) {
	String palinText = "가";
	for (int j = 0; j < i; j++) {
	palinText += "가";
	}
	String encrypt = Aes256Util.encryptByRandom(palinText, key);
	String decyprt = Aes256Util.decrypt(encrypt, key);
	System.out.println(encrypt);
	System.out.println(decyprt);
	// ValidateUtil.isTrue(palinText.equals(decyprt), decyprt);
	}
	}
	}

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