请问DES加密怎么解密呀！

[Carman11]

我有一个DES加密的文本aaa.txt。怎么才能正确显示出文本。
FileStream fs=new FileStream("c:\\aaa.txt",FileMode.Open,FileAccess.Read);
StreamReader sr=new StreamReader(fs,Encoding.Default);
string text11=sr.ReadToEnd();
Console.WriteLine(text11);
DESCryptoServiceProvider des=new DESCryptoServiceProvider();
ICryptoTransform destran=des.CreateDecryptor();
CryptoStream crystr=new CryptoStream(fs,destran,CryptoStreamMode.Read);
Console.WriteLine((new StreamReader(crystr,new UnicodeEncoding())).ReadToEnd());
Console.ReadLine();