输入数据不是一个完整的块。c#

它在

cs.Close（）处向我抛出一个错误
错误在于输入数据不是完整的块

我实际上在做密码加密和解密。
加密没有问题，但当谈到解密，首先它说不能从基64转换，所以我补充说

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.IO;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Security.Cryptography;
namespace SOMaintenance.App_Code
{
    public class passwordsecurity
    {

        public string Encrypt(string clearText)
        {
            string EncryptionKey = "SWISSLOGMALAYSIA";
            byte[] clearBytes = Encoding.Unicode.GetBytes(clearText);
            using (Aes encryptor = Aes.Create())
            {
                Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
                encryptor.Key = pdb.GetBytes(32);
                encryptor.IV = pdb.GetBytes(16);
                using (MemoryStream ms = new MemoryStream())
                {
                    using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
                    {
                        cs.Write(clearBytes, 0, clearBytes.Length);
                        cs.Close();
                    }
                    clearText = Convert.ToBase64String(ms.ToArray());
                }
            }
            return clearText;
        }

        internal string Decrypt(string cipherText)
        {
            int mod4 = cipherText.Length % 4;
            if (mod4 > 0)
            {
                cipherText += new string('=', 4 - mod4);
            }
            string EncryptionKey = "SWISSLOGMALAYSIA";
            byte[] cipherBytes = Convert.FromBase64String(cipherText);
            using (Aes encryptor = Aes.Create())
            {
                Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
                encryptor.Key = pdb.GetBytes(32);
                encryptor.IV = pdb.GetBytes(16);
                using (MemoryStream ms = new MemoryStream())
                {
                    using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
                    {
                        cs.Write(cipherBytes, 0, cipherBytes.Length);
                        cs.Close();
                    }
                    cipherText = Encoding.Unicode.GetString(ms.ToArray());
                }
            }
            return cipherText;
        }
    }
}

然后它把我现在面临的错误抛给了我。希望有人能在这方面帮助我。
感谢并感谢
oracle数据库是如何进入的？因为我是从oracle数据库检索的，我不确定数据库中的数据类型是否会影响它。。起初，我无法从base 64转换，我只是想为能够帮助我的人提供更多信息。。
int mod4 = cipherText.Length % 4;
if (mod4 > 0)
{
   cipherText += new string('=', 4 - mod4);
}