Unhadelded Exception Occurs When using RSACryptoServic eProvider

[khubieb]

Simply I am trying to use RSACryptoServic eProvider to generate a key
pair, send the public key to a service that will retrieve me data,
encrypt it with my public key, send the encrypted data back for me to
decrypt the data and use it. below is a code sample that simulates my
task. It works just fine, however, when I turn impersonation to true in
my web.config file and after a random number of attempts to invoke my
page, an unhandled exception is fired somewhere in the Crypto Service
Provider causing the aspnet_wp process to restart. I've caught the
exception by registring an HTTP Module to listen to the
AppDomain.Curre ntDomain.Unhand ledException event and this is the
exception I get

type=System.Sec urity.Cryptogra phy.Cryptograph icException

message=Keyset does not exist
stack=
at
System.Security .Cryptography.C ryptographicExc eption.ThrowCry ptogaphicExcept ion(Int32
hr)
at System.Security .Cryptography.S afeProvHandle._ FreeCSP(IntPtr
pProvCtx)
at System.Security .Cryptography.S afeProvHandle.R eleaseHandle()
at System.Runtime. InteropServices .SafeHandle.Int ernalFinalize()
at System.Runtime. InteropServices .SafeHandle.Dis pose(Boolean
disposing)
at System.Runtime. InteropServices .SafeHandle.Fin alize()

..

If I turn impersonation to false in web.config the exception doesn't
fire. I don't know where does this exception occure.
Also I've noticed that I missed to release the resources used by
RSACryptoServic eProvider by invoking the
RSACryptoServic eProvider.Clear () method. when calling this method the
exception seems to cease to occure.

I am just curious to know what is happening? what is the relation
between impersonation and RSACryptoServic eProvider? why isn't it caught
by the catch block? What is the thread that fires the exception? ...

here is the code of my web form

using System;
using System.Data;
using System.Configur ation;
using System.Web;
using System.Web.Secu rity;
using System.Web.UI;
using System.Web.UI.W ebControls;
using System.Web.UI.W ebControls.WebP arts;
using System.Web.UI.H tmlControls;

using System.Security .Cryptography;
using System.Text;

public partial class _Default : System.Web.UI.P age
{
protected void Page_Load(objec t sender, EventArgs e)
{
}
protected void btnRefresh_Serv erClick(object sender, EventArgs e)
{
try
{
CspParameters cspParam = new CspParameters() ;
cspParam.Flags = CspProviderFlag s.UseMachineKey Store;
RSACryptoServic eProvider pair = new
RSACryptoServic eProvider(cspPa ram);
string keyInfo = pair.ToXmlStrin g(false);
string encryptedData = GetSecureData(k eyInfo);
byte[] encrptedBytes =
Convert.FromBas e64String(encry ptedData);
byte[] decryptedBytes = pair.Decrypt(en crptedBytes, true);

string decrypedData =
Encoding.ASCII. GetString(decry ptedBytes);
//pair.Clear();
txtEnctptedData .Value = encryptedData;
txtDecryptedDat a.Value = decrypedData;
}
catch (Exception ex)
{
txtDecryptedDat a.Value = ex.Message;
}
}

private string GetSecureData(s tring publicKey)
{
CspParameters cspParam = new CspParameters() ;
cspParam.Flags = CspProviderFlag s.UseMachineKey Store;
RSACryptoServic eProvider pair = new
RSACryptoServic eProvider(cspPa ram);
pair.FromXmlStr ing(publicKey);

byte[] dataBytes = Encoding.ASCII. GetBytes("Hello World!!");
dataBytes = pair.Encrypt(da taBytes, true);

return Convert.ToBase6 4String(dataByt es);
}
}