AES key generator (from string or none), encrypt and decrypt in java

SymetricCrypto.java

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package network_security;

import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.KeySpec;
import java.util.Arrays;
import java.util.Base64;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

/**
 *
 * @author Admin
 */
public class SymmetricCryptor {

    //hằng xác định thuật toán mã hóa
    private final String Algorithm = "AES";
    //khóa
    private SecretKey secretKey;
    //bộ sinh khóa theo thuật toán đã chọn
    private KeyGenerator keyGen;
    //bộ mã
    private Cipher cipher;

    public SymmetricCryptor() {

    }

    // Tạo khóa không sử dụng chuỗi
    public void createSymetricKey() throws Exception {
        //khởi tạo bộ sinh khóa
        keyGen = KeyGenerator.getInstance(Algorithm);
        //sinh khóa
        secretKey = keyGen.generateKey();
    }

    // Tạo khóa sử dụng chuỗi
    public void createSymetricKeyFromPassword(String keystring) throws Exception {
        byte[] key = new byte[16];
        key = keystring.getBytes("UTF-8");
        MessageDigest sha = MessageDigest.getInstance("SHA-1");
        key = sha.digest(key);
        key = Arrays.copyOf(key, 16);

        secretKey = new SecretKeySpec(key, "AES");
    }

    public SecretKey getSecretKey() {
        return secretKey;
    }

    public String encryptText(String msg, SecretKey key)
            throws Exception {
        //tạo bộ mã
        cipher = Cipher.getInstance(Algorithm);
        cipher.init(Cipher.ENCRYPT_MODE, key);
        return Base64.getEncoder().encodeToString(
                cipher.doFinal(msg.getBytes("UTF-8")));
    }

    public String decryptText(String msg, SecretKey key)
            throws Exception {
        cipher = Cipher.getInstance(Algorithm);
        cipher.init(Cipher.DECRYPT_MODE, key);
        return new String(cipher.doFinal(
                Base64.getDecoder().decode(msg)), "UTF-8");
    }
    
    public static void main(String[] args) throws Exception {
        SymmetricCryptor SC = new SymmetricCryptor();
        SC.createSymetricKeyFromPassword("daicaphong");
        String msg = "Nguyễn Văn An";
        String encrypted_msg = 
                SC.encryptText(msg, SC.getSecretKey());
        System.out.println("Plain text: " + msg);
        System.out.println("Encrypted text: " + encrypted_msg);
        String decrypted_msg =
                SC.decryptText(encrypted_msg, SC.getSecretKey());
        System.out.println("Decrypted text: " + decrypted_msg);
    }
}