import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

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



import sun.misc.Cache;

public class cipher {

    private String key;
    private SecretKeySpec keySpec;
    private Cipher cipher;

    public void setSecretKey(String key)
    {
        this.key = key;
    }
    public void setAlgorithm(String algorithm)
    {
        byte[] raw = stringToBytes(key);
        keySpec = new SecretKeySpec(raw , algorithm);
        try
        {
            cipher = Cipher.getInstance(algorithm);
        }
        catch(NoSuchAlgorithmException e)
        {
            e.printStackTrace();
        }
        catch(NoSuchPaddingException e)
        {
            e.printStackTrace();
        }
    }

    public String encrypt(String str)
    {
        try
        {
            byte[] encrypted = null;
            synchronized (cipher)
            {
                cipher.init(Cipher, ENCRYPT_MODE,keySpec);
                encrypted = cipher.doFinal(str,getBytes());
            }
            return new String(Hex,encodeHex(encrypted));
        }
        catch(Exception e)
        {
            throw new RuntimeException("encryption Fail",e);
        }
    }
    public String decrypt(String str)
    {
        try
        {
            byte[] decrypted = null;
            synchronized (cipher)
            {
                cipher.init(Cipher, DECRYPT_MODE,keySpec);
                decrypted = cipher.doFinal(str,getBytes());
            }
            return new String(Hex,encodeHex(decrypted));
        }
        catch(Exception e)
        {
            throw new RuntimeException("decryption Fial",e);
        }
    }

    public static String generateRandomSecretKey(String algorithm) throws Exception
    {
        KeyGenerator KeyGen = KeyGenerator.getInstance(algorithm);
        KeyGen.init(128);
        SecretKey key = KeyGen.generateKey();
        byte[] raw  = key.getEncoded();
        return bytesToString(raw);
    }

    private static String bytesToString(byte[] bytes)
    {
        byte[] b2 = new byte[bytes.length+1];
        b2[0] = 1;
        System.arraycopy(bytes, 0, b2, 1, bytes.length);
        return new BigInteger(b2).toString(Character.MAX_RADIX);
    }

    private static byte[] stringToBytes(String str)
    {
        byte[] bytes = new BigInteger(str,Character.MAX_RADIX).toByteArray();
        return Arrays.copyOfRange(bytes, 1, bytes.length);
    }
    public static void main(String args[]) throws Exception
    {
        String key = generateRandomSecretKey("AES");
        System.out.println(key);
        cipher cs = new cipher();
        cs.setSecretKey(key);
        cs.setAlgorithm("AES");
        String encStr = cs.encrypt("This is Java Class");
        System.out.println(encStr);
        String decStr = cs.decrypt(encStr);
        System.out.println(decStr);
    }



}