使用的DES对称加密

  在网站使用Cookie或者存放数据到数据库中的时候时常会用到加密解密，md5非常好用，但是有的时候需要进行逆运算。那么此时DES对称加密就比较好用了。设定一个密钥，然后对所有的数据进行加密。代码介绍如下，事先声明仅为小弟个人理解，请各位多多指教
  Imports System
  Imports System.IO
  Imports System.Text
  Imports System.Diagnostics
  Imports System.Security.Cryptography
  Imports System.Text.RegularEXPRessions

  '使用标准DES对称加密
  Public Function EncryptDes(ByVal SourceStr As String) As String

　  'get encodekey string from web.config
　  Dim skey As String
　  skey = ConfigurationSettings.AppSettings("EnCodeKey")

　  'put the input string into the byte array
　  Dim des As DESCryptoServiceProvider = New DESCryptoServiceProvider()
　  Dim inputByteArray As Byte()
　  inputByteArray = Encoding.Default.GetBytes(SourceStr)

　  'set encrypt object and skey
　  des.Key = ASCIIEncoding.ASCII.GetBytes(skey)
　  des.IV = ASCIIEncoding.ASCII.GetBytes(skey)
　  Dim ms As MemoryStream = New MemoryStream()
　  Dim cs As CryptoStream = New CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write)
　  Dim sw As StreamWriter = New StreamWriter(cs)
　  sw.Write(SourceStr)
　  sw.Flush()
　  cs.FlushFinalBlock()
　  ms.Flush()
　  Return Convert.ToBase64String(ms.GetBuffer(), 0, ms.Length)

  End Function

  '使用标准DES对称解密
  Public Function DecryptDes(ByVal SourceStr As String) As String

　  'get encodekey string from web.config
　  Dim sKey As String
　  sKey = ConfigurationSettings.AppSettings("EnCodeKey")

　  'put the input string into the byte array
　  Dim des As DESCryptoServiceProvider = New DESCryptoServiceProvider()

　  des.Key = ASCIIEncoding.ASCII.GetBytes(sKey)
　  des.IV = ASCIIEncoding.ASCII.GetBytes(sKey)

　  Dim buffer As Byte() = Convert.FromBase64String(SourceStr)

　  Dim ms As MemoryStream = New MemoryStream(buffer)
　  Dim cs As CryptoStream = New CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Read)
　  Dim sr As StreamReader = New StreamReader(cs)
　  Return sr.ReadToEnd()

  End Function