AES CryptoUtils

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.SecureRandom;
import java.util.Base64;

import static java.nio.charset.StandardCharsets.UTF_8;

public class CryptoUtils {

    private static AesCrypto textCrypto = null; // key for text data

    public static void init(String key) {
        if (textCrypto == null) {
            textCrypto = new AesCrypto(key);
        }
    }


    public static String decryptText(final String cypherData) {
        return new String(textCrypto.decryptBytes(TrimBase64.decode(cypherData)), UTF_8);
    }

    public static String encryptText(final String planData) {
        return TrimBase64.encode(textCrypto.encryptBytes(planData.getBytes(UTF_8)));
    }

    private static class TrimBase64 {
        private static byte[] decode(String text) {
            if (text == null) {
                return null;
            }
            // padding trailing '='
            int length = text.length();
            switch (length % 4) {
                case 2:
                    text += "==";
                    break;
                case 1:
                    text += "===";
                    break;
                case 3:
                    text += "=";
                    break;
                default:
                    break;
            }
            return Base64.getDecoder().decode(text);
        }

        private static String encode(byte[] data) {
            // trim trailing '='
            return data == null ? null : Base64.getEncoder().encodeToString(data).replaceAll("=*$", "");
        }
    }

    private static class AesCrypto {

        private final SecretKeySpec keySpec;
        private final SecureRandom srandom;

        AesCrypto(String hexKey) {
            if (!testKeys(hexKey)) {
                throw new RuntimeException("AES Key invalid");
            }
            keySpec = new SecretKeySpec(fromHex(hexKey), "AES");
            srandom = new SecureRandom();
        }

        /**
         * AES-128/192/256 allowed
         *
         * @param hexKey
         * @return
         */
        private boolean testKeys(String hexKey) {
            return hexKey != null && (hexKey.length() == 32 || hexKey.length() == 48 || hexKey.length() == 64);
        }

        private byte[] fromHex(String hexStr) {
            if (hexStr == null) {
                return null;
            }
            int length = hexStr.length();
            if (length % 2 == 1) {
                return null;
            }
            int byteLength = length / 2;
            byte[] raw = new byte[byteLength];
            for (int i = 0; i < byteLength; i++) {
                raw[i] = (byte) Integer.parseInt(hexStr.substring(i + i, i + i + 2), 16);
            }
            return raw;
        }

        private byte[] decryptBytes(byte[] sBytes) {
            if (sBytes == null) {
                return null;
            }
            try {
                Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
                int ivSize = cipher.getBlockSize();
                IvParameterSpec ivSpec = new IvParameterSpec(sBytes, 0, ivSize);
                cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
                byte[] payload = cipher.doFinal(sBytes, ivSize, sBytes.length - ivSize);
                return payload;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }

        private byte[] encryptBytes(byte[] sBytes) {
            if (sBytes == null) {
                return null;
            }
            try {
                Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
                byte[] iv = new byte[cipher.getBlockSize()];
                srandom.nextBytes(iv);
                IvParameterSpec ivSpec = new IvParameterSpec(iv);
                cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
                byte[] payload = cipher.doFinal(sBytes);
                byte[] encrypted = new byte[iv.length + payload.length];
                System.arraycopy(iv, 0, encrypted, 0, iv.length);
                System.arraycopy(payload, 0, encrypted, iv.length, payload.length);
                return encrypted;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }
    }
}