如何解決silverlight 2/3中缺少的加密類？

我正在做一些我不控制的服務器端服務的工作。以下工作在標準C＃罰款，但失敗了（由於缺少加密類）在Silverlight 2和3如何解決silverlight 2/3中缺少的加密類？

static String DecryptString() 
    { 
     s = "<cipherTextHere>"; 

     byte[] toDecryptArray = Convert.FromBase64String(s); 
     string key = "<key here>"; 

     byte[] keyArray = new byte[key.Length/2]; 
     for (int i = 0; i < keyArray.Length; i++) 
     { 
      keyArray[i] = Convert.ToByte(Convert.ToInt32(key.Substring(i * 2, 2), 16)); 
     } 

     using (var algo = new System.Security.Cryptography.AesManaged()) 
     { 

      // The two lines below are the problem 
      // as SL does not give me the option to select padding or ciphermode 
      algo.Padding = PaddingMode.PKCS7; 
      algo.Mode = CipherMode.ECB; 

      algo.Key = keyArray; 

      ICryptoTransform cTransform = algo.CreateDecryptor(); 
      byte[] resultArray = cTransform.TransformFinalBlock(
           toDecryptArray, 0, toDecryptArray.Length); 

      return (UTF8Encoding.UTF8.GetString(resultArray, 0, resultArray.Length)); 

     } 
    }

有什麼選擇？

來源

2009-06-02 aronchick