C# AES128/AES256 암호화 복호화(Rijndael)

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Threading;
using System.Security.Cryptography;

namespace AESENC
{
    public class AES
    {
        //AES_256 암호화
        public String AESEncrypt256(String Input, String key)
        {
            RijndaelManaged aes = new RijndaelManaged();
            aes.KeySize = 256;
            aes.BlockSize = 128;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;
            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

            var encrypt = aes.CreateEncryptor(aes.Key, aes.IV);
            byte[] xBuff = null;
            using (var ms = new MemoryStream())
            {
                using (var cs = new CryptoStream(ms, encrypt, CryptoStreamMode.Write))
                {
                    byte[] xXml = Encoding.UTF8.GetBytes(Input);
                    cs.Write(xXml, 0, xXml.Length);
                }

                xBuff = ms.ToArray();
            }

            String Output = Convert.ToBase64String(xBuff);
            return Output;
        }


        //AES_256 복호화
        public String AESDecrypt256(String Input, String key)
        {
            RijndaelManaged aes = new RijndaelManaged();
            aes.KeySize = 256;
            aes.BlockSize = 128;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;
            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

            var decrypt = aes.CreateDecryptor();
            byte[] xBuff = null;
            using (var ms = new MemoryStream())
            {
                using (var cs = new CryptoStream(ms, decrypt, CryptoStreamMode.Write))
                {
                    byte[] xXml = Convert.FromBase64String(Input);
                    cs.Write(xXml, 0, xXml.Length);
                }

                xBuff = ms.ToArray();
            }

            String Output = Encoding.UTF8.GetString(xBuff);
            return Output;
        }


        //AES_128 암호화
        public String AESEncrypt128(String Input, String key)
        {
            
            RijndaelManaged RijndaelCipher = new RijndaelManaged();

            byte[] PlainText = System.Text.Encoding.Unicode.GetBytes(Input);
            byte[] Salt = Encoding.ASCII.GetBytes(key.Length.ToString());

            PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(key, Salt);
            ICryptoTransform Encryptor = RijndaelCipher.CreateEncryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16));

            MemoryStream memoryStream = new MemoryStream();
            CryptoStream cryptoStream = new CryptoStream(memoryStream, Encryptor, CryptoStreamMode.Write);

            cryptoStream.Write(PlainText, 0, PlainText.Length);
            cryptoStream.FlushFinalBlock();
            
            byte[] CipherBytes = memoryStream.ToArray();

            memoryStream.Close();
            cryptoStream.Close();

            string EncryptedData = Convert.ToBase64String(CipherBytes);

            return EncryptedData;
        }

        //AE_S128 복호화
        public String AESDecrypt128(String Input, String key)
        {
            RijndaelManaged RijndaelCipher = new RijndaelManaged();

            byte[] EncryptedData = Convert.FromBase64String(Input);
            byte[] Salt = Encoding.ASCII.GetBytes(key.Length.ToString());

            PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(key, Salt);
            ICryptoTransform Decryptor = RijndaelCipher.CreateDecryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16));
            MemoryStream memoryStream = new MemoryStream(EncryptedData);
            CryptoStream cryptoStream = new CryptoStream(memoryStream, Decryptor, CryptoStreamMode.Read);

            byte[] PlainText = new byte[EncryptedData.Length];

            int DecryptedCount = cryptoStream.Read(PlainText, 0, PlainText.Length);

            memoryStream.Close();
            cryptoStream.Close();

            string DecryptedData = Encoding.Unicode.GetString(PlainText, 0, DecryptedCount);

            return DecryptedData;
        }
    }
}