Java using AES 256 and 128 Symmetric-key encryption

Question

I am new in cipher technology. I found this code to do Symmetric Encryption.

byte[] key = //... secret sequence of bytes
byte[] dataToSend = ...
Cipher c = C         


        

Answer 1

The Answer for 128 bit

The following method is to encrypt a string (valueEnc) with AES encryption:

private static final String ALGORITHM = "AES"; 

public String encrypt(final String valueEnc, final String secKey) { 

    String encryptedVal = null;

    try {
        final Key key = generateKeyFromString(secKey);
        final Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.ENCRYPT_MODE, key);
        final byte[] encValue = c.doFinal(valueEnc.getBytes());
        encryptedVal = new BASE64Encoder().encode(encValue);
    } catch(Exception ex) {
        System.out.println("The Exception is=" + ex);
    }

    return encryptedVal;
}

The next method will decrypt the AES encrypted string (encryptedVal):

    public String decrypt(final String encryptedValue, final String secretKey) {

    String decryptedValue = null;

    try {

        final Key key = generateKeyFromString(secretKey);
        final Cipher c = Cipher.getInstance(ALGORITHM);
        c.init(Cipher.DECRYPT_MODE, key);
        final byte[] decorVal = new BASE64Decoder().decodeBuffer(encryptedValue);
        final byte[] decValue = c.doFinal(decorVal);
        decryptedValue = new String(decValue);
    } catch(Exception ex) {
        System.out.println("The Exception is=" + ex);
    }

    return decryptedValue;
}

The secKey is a 128-bit key, which is encoded in the BASE64Encoder. The BASE64Decoder in the following method generates an appropriate 128-bit key

private Key generateKeyFromString(final String secKey) throws Exception {
    final byte[] keyVal = new BASE64Decoder().decodeBuffer(secKey);
    final Key key = new SecretKeySpec(keyVal, ALGORITHM);
    return key;
}