How do encryption methods work?

Well, I read on encryption techniques. I found out that there are 3 types.

• Hashing encryption
• Symmetric methods
• Asymmetrical shapes

I don't understand hasing Encryption and some parts of AES in Symmetric method.

Hashing Problem Encryption :: I read - "once the data is encrypted, the process cannot be canceled or decrypted." What is my question, why would anyone use this method if you can only encrypt the data but cannot decrypt it? or I'm wrong?

The problem with AES :: Below is the code I found:

public class AES {

    private static SecretKeySpec secretKey;
    private static byte[] key;
    private static String decryptedString;
    private static String encryptedString;

    public static void setKey(String myKey) {

        MessageDigest sha = null;
        try {
            key = myKey.getBytes("UTF-8");
            System.out.println(key.length);
            sha = MessageDigest.getInstance("SHA-1");
            key = sha.digest(key);
            key = Arrays.copyOf(key, 16); // use only first 128 bit
            System.out.println(key.length);
            System.out.println(new String(key, "UTF-8"));
            secretKey = new SecretKeySpec(key, "AES");
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static String getDecryptedString() {
        return decryptedString;
    }

    public static void setDecryptedString(String decryptedString) {
        AES.decryptedString = decryptedString;
    }

    public static String getEncryptedString() {
        return encryptedString;
    }

    public static void setEncryptedString(String encryptedString) {
        AES.encryptedString = encryptedString;
    }

    public static String encrypt(String strToEncrypt) {
        try {
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            setEncryptedString(Base64.encodeBase64String(cipher.doFinal(strToEncrypt.getBytes("UTF-8"))));
        } catch (Exception e) {
            System.out.println("Error while encrypting: " + e.toString());
        }
        return null;
    }

    public static String decrypt(String strToDecrypt) {
        try {
            Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            setDecryptedString(new String(cipher.doFinal(Base64.decodeBase64(strToDecrypt))));
        } catch (Exception e) {
            System.out.println("Error while decrypting: " + e.toString());
        }
        return null;
    }
}

      

        
        
        
      

    

Each cipher encrypts and decrypts data in blocks of 128 bits using cryptographic keys of 128, 192 and 256 bits, respectively.

So in the code:

key = Arrays.copyOf(key, 16);

      

        
        
        
      

    

its using 128 bit keys, right?

But what is base64 inside encryption and decryption methods?

public static String encrypt(String strToEncrypt) {
    try {
        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        setEncryptedString(Base64.encodeBase64String(cipher.doFinal(strToEncrypt.getBytes("UTF-8"))));
    }
}