Java AES Examples

Java AES 암호화/복호화 예제, 16바이트(128비트)키를 사용하는 경우

package encrypt;


import javax.crypto.*;
import javax.crypto.spec.*;

/**
* This program generates a AES key, retrieves its raw bytes, and then
* reinstantiates a AES key from the key bytes. The reinstantiated key is used
* to initialize a AES cipher for encryption and decryption.
*/
public class AESDemo {

/**
* Turns array of bytes into string
*
* @param buf Array of bytes to convert to hex string
* @return Generated hex string
*/
public static String asHex(byte buf[]) {
	StringBuffer strbuf = new StringBuffer(buf.length * 2);
	int i;

	for (i = 0; i < buf.length; i++) {
	  if (((int) buf[i] & 0xff) < 0x10)
		  strbuf.append("0");

	  strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
	}

	 return strbuf.toString();
}

public static void main(String[] args) throws Exception {
	String message = "This is just an example";
	
	/* 키를 동적으로 생성하는 경우의 코드
	// Get the KeyGenerator
	KeyGenerator kgen = KeyGenerator.getInstance("AES");
	kgen.init(128); // 192 and 256 bits may not be available
	
	// Generate the secret key specs.
	SecretKey skey = kgen.generateKey();
	
	byte[] raw = skey.getEncoded();
	
	//SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
	*/
	
	// 미리 주어진 키를 사용하는 경우, 128비트(16바이트)키를 사용하는 예
	SecretKeySpec skeySpec = new SecretKeySpec("0123456789123456".getBytes(), "AES");
	
	// Instantiate the cipher
	Cipher cipher = Cipher.getInstance("AES");
	
	cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
	
	byte[] encrypted = cipher.doFinal(message.getBytes());
	System.out.println("encrypted string: " + asHex(encrypted));
	
	cipher.init(Cipher.DECRYPT_MODE, skeySpec);
	
	byte[] original = cipher.doFinal(encrypted);
	String originalString = new String(original);
	System.out.println("Original string: " + originalString + " " + asHex(original));
}

}

package encrypt;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

public class AESExample {
  
 /*
  * AES의 경우 128, 192, 256bit의 키 길이를 지원합니다
  * key 에 해당하는 문자열을 16byte(128) 또는 24byte(192) 또는 32byte(256) 생성
  */

    public static String key = "0123456789123456";

    /**
     * hex to byte[] : 16진수 문자열을 바이트 배열로 변환한다.
     *
     * @param hex    hex string
     * @return
     */
    public static byte[] hexToByteArray(String hex) {
        if (hex == null || hex.length() == 0) {
            return null;
        }

        byte[] ba = new byte[hex.length() / 2];
        for (int i = 0; i < ba.length; i++) {
            ba[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
        }
        return ba;
    }

    /**
     * byte[] to hex : unsigned byte(바이트) 배열을 16진수 문자열로 바꾼다.
     *
     * @param ba        byte[]
     * @return
     */
    public static String byteArrayToHex(byte[] ba) {
        if (ba == null || ba.length == 0) {
            return null;
        }

        StringBuffer sb = new StringBuffer(ba.length * 2);
        String hexNumber;
        for (int x = 0; x < ba.length; x++) {
            hexNumber = "0" + Integer.toHexString(0xff & ba[x]);

            sb.append(hexNumber.substring(hexNumber.length() - 2));
        }
        return sb.toString();
    }

    /**
     * AES 방식의 암호화
     *
     * @param message
     * @return
     * @throws Exception
     */
    public static String encrypt(String message) throws Exception {

        // use key coss2
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");

        // Instantiate the cipher
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

        byte[] encrypted = cipher.doFinal(message.getBytes());
        return byteArrayToHex(encrypted);
    }

    /**
     * AES 방식의 복호화
     *
     * @param message
     * @return
     * @throws Exception
     */
    public static String decrypt(String encrypted) throws Exception {

        // use key coss2
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");

        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        byte[] original = cipher.doFinal(hexToByteArray(encrypted));
        String originalString = new String(original);
        return originalString;
    }
  
    public static void main(String[] args)
    {
        try {
            String encrypt = encrypt("test1234");
            System.out.println("origin str = "+"test1234");
            System.out.println("encrypt str = "+encrypt);
          
            String decrypt = decrypt(encrypt);
            System.out.println("decrypt str = "+decrypt);
          
        } catch (Exception e) {
            e.printStackTrace();
        }
      
    }

}