------------IV的作用：
為了保證數據的安全，.NET基類庫中提供的私鑰算法類使用稱作密碼塊鏈（CBC，Cipher Block Chaining）的鏈模式，算法使用一個密鑰和一個初始化向量（IV，Initialization Vector）對數據執行加密轉換。密鑰和初始化向量IV一起決定如何加密數據，以及如何將數據解密為原始數據。通信雙方都必須知道這個密鑰和初始化向量才能夠加密和解密數據。

初始化向量IV的作用:防止隨機產生的明文和密文相同
------------加密類：
#region public static DES encrypt for string
///<summary>
///static DES encrypt for string
///</summary>
///<returns>encrypted string</returns>
///<param name="OriginalString">original string</param>
///<param name="EncryptKey">encrypt key, must 8 characters</param>
///<param name="EncryptOffset">encrypt IV, must >= 8 characters</param>
public static string DesEncryptString(string OriginalString, string EncryptKey, string EncryptOffset)
{
byte[] btKey = Encoding.Default.GetBytes(EncryptKey);
byte[] btIV = Encoding.Default.GetBytes(EncryptOffset);
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
using (MemoryStream ms = new MemoryStream())
{
byte[] inData = Encoding.Default.GetBytes(OriginalString);
try
{
using (CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(inData, 0, inData.Length);
cs.FlushFinalBlock();
}

return Convert.ToBase64String(ms.ToArray());
}
catch
{
return "";
}
}
}

#endregion

#region public static DES decrypt for string
///<summary>
///DES decrypt for string
///</summary>
///<returns>dncrypted string</returns>
///<param name="EncryptedString">original string</param>
///<param name="EncryptKey">encrypt key, must 8 characters</param>
///<param name="EncryptOffset">encrypt IV, must >= 8 characters</param>
public static string DesDecryptString(string EncryptedString, string EncryptKey, string EncryptOffset)
{
byte[] btKey = Encoding.Default.GetBytes(EncryptKey);
byte[] btIV = Encoding.Default.GetBytes(EncryptOffset);
DESCryptoServiceProvider des = new DESCryptoServiceProvider();

using (MemoryStream ms = new MemoryStream())
{
byte[] inData = Convert.FromBase64String(EncryptedString);
try
{
using (CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(inData, 0, inData.Length);
cs.FlushFinalBlock();
}

return Encoding.Default.GetString(ms.ToArray());
}
catch
{
return "";
}
}
}
#endregion

#region public static DES encrypt for file
/// <summary>
/// DES encrypt for file
/// </summary>
/// <param name="m_InFilePath">Input file path</param>
/// <param name="m_OutFilePath">Output file path</param>
/// <param name="strEncrKey">key, must 8 characters</param>
///<param name="strEncrOffset">encrypt IV, must >= 8 characters</param>
/// <returns>success or not</returns>
public static bool DESEncryptFile(string m_InFilePath, string m_OutFilePath, string strEncrKey, string strEncrOffset)
{
if (File.Exists(m_InFilePath) == false)
{
return false;
}

byte[] btKey = Encoding.Default.GetBytes(strEncrKey);
byte[] btIV = Encoding.Default.GetBytes(strEncrOffset);
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
byte[] btFile = File.ReadAllBytes(m_InFilePath);

using (FileStream fs = new FileStream(m_OutFilePath, FileMode.Create, FileAccess.Write))
{
try
{
using (CryptoStream cs = new CryptoStream(fs, des.CreateEncryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(btFile, 0, btFile.Length);
cs.FlushFinalBlock();
}

fs.Close();
}
catch
{
fs.Close();
return false;
}
}

return true;
}
#endregion

#region public static DES decrypt for file
/// <summary>
/// DES decrypt for file
/// </summary>
/// <param name="m_InFilePath">Input file path</param>
/// <param name="m_OutFilePath">Output file path</param>
/// <param name="sDecrKey">key, must 8 characters</param>
///<param name="strEncrOffset">encrypt IV, must >= 8 characters</param>
/// <returns>success or not</returns>
public static bool DESDecryptFile(string m_InFilePath, string m_OutFilePath, string sDecrKey, string strEncrOffset)
{
if (File.Exists(m_InFilePath) == false)
{
return false;
}

byte[] btKey = Encoding.Default.GetBytes(sDecrKey);
byte[] btIV = Encoding.Default.GetBytes(strEncrOffset);
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
byte[] btFile = File.ReadAllBytes(m_InFilePath);

using (FileStream fs = new FileStream(m_OutFilePath, FileMode.Create, FileAccess.Write))
{
try
{
using (CryptoStream cs = new CryptoStream(fs, des.CreateDecryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(btFile, 0, btFile.Length);
cs.FlushFinalBlock();
}
fs.Close();
}
catch
{
fs.Close();
return false;
}
}

return true;
}
#endregion

#region public static AES/CBC/PKCS7Padding encrypt for string
///<summary>
///static AES/CBC/PKCS7Padding encrypt for string
///</summary>
///<returns>encrypted string</returns>
///<param name="OriginalString">original string</param>
///<param name="EncryptKey">encrypt key, must 8 characters</param>
///<param name="EncryptOffset">encrypt IV, must >= 8 characters</param>
public static string AESEncryptString(string OriginalString, string EncryptKey, string EncryptOffset)
{
try
{
byte[] btKey = Encoding.Default.GetBytes(EncryptKey);
byte[] btIV = Encoding.Default.GetBytes(EncryptOffset);
RijndaelManaged rDel = new RijndaelManaged();
rDel.Key = btKey;
rDel.Mode = CipherMode.CBC;
rDel.Padding = PaddingMode.PKCS7;
using (MemoryStream ms = new MemoryStream())
{
byte[] inData = Encoding.Default.GetBytes(OriginalString);
using (CryptoStream cs = new CryptoStream(ms, rDel.CreateEncryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(inData, 0, inData.Length);
cs.FlushFinalBlock();
}
return Convert.ToBase64String(ms.ToArray());
}
}
catch
{
return "";
}
}
#endregion

#region public static AES/CBC/PKCS7Padding decrypt for string
///<summary>
///AES/CBC/PKCS7Padding decrypt for string
///</summary>
///<returns>dncrypted string</returns>
///<param name="EncryptedString">original string</param>
///<param name="EncryptKey">encrypt key, must 8 characters</param>
///<param name="EncryptOffset">encrypt IV, must >= 8 characters</param>
public static string AESDecryptString(string EncryptedString, string EncryptKey, string EncryptOffset)
{
try
{
byte[] btKey = Encoding.Default.GetBytes(EncryptKey);
byte[] btIV = Encoding.Default.GetBytes(EncryptOffset);
RijndaelManaged rDel = new RijndaelManaged();
rDel.Key = btKey;
rDel.Mode = CipherMode.CBC;
rDel.Padding = PaddingMode.PKCS7;
using (MemoryStream ms = new MemoryStream())
{
byte[] inData = Convert.FromBase64String(EncryptedString);
using (CryptoStream cs = new CryptoStream(ms, rDel.CreateDecryptor(btKey, btIV), CryptoStreamMode.Write))
{
cs.Write(inData, 0, inData.Length);
cs.FlushFinalBlock();
}
return Encoding.Default.GetString(ms.ToArray());
}
}
catch
{
return "";
}
}
#endregion
}

des和Rijndael加密