private AFLN2Prefix DecomposePrefix(byte[] data)
{
AFLN2Prefix prefixObject = new AFLN2Prefix();
List <Tuple <int, int> > paddingIndexes = new List <Tuple <int, int> >();
string prefix = null;
string dataString = Encoding.UTF8.GetString(data);
int prefixEndIndex = dataString.IndexOf(AFLN2Prefix.PrefixEndFormat) + 1;
prefix = dataString.Substring(0, prefixEndIndex);
prefixObject.Content = prefix;
prefix = prefix.Replace(AFLN2Prefix.PrefixBeginFormat, "");
prefix = prefix.Replace(AFLN2Prefix.PrefixEndFormat, "");
if (prefix.Length > 0)
{
prefix = prefix.Substring(1);
prefix = prefix.Substring(0, prefix.Length - 1);
string[] splittedPrefix = prefix.Split(new string[] { String.Format("{0}{1}{2}", AFLN2Prefix.TupleEnd, AFLN2Prefix.IndexesSeparator, AFLN2Prefix.TupleBegin) }, StringSplitOptions.None);
for (int i = 0; i < splittedPrefix.Length; i++)
{
int[] items = splittedPrefix[i].Split(new string[] { AFLN2Prefix.IndexesSeparator }, StringSplitOptions.None).Select(x => Convert.ToInt32(x)).ToArray();
paddingIndexes.Add(Tuple.Create(items[0], items[1]));
}
}
prefixObject.PaddingIndexes = paddingIndexes;
return(prefixObject);
}
public string Decrypt(string data)
{
byte[] dataBytes = null;
byte[] dataBytesAux = Convert.FromBase64String(data);
List <byte> decryptedData = new List <byte>();
AFLN2Prefix prefix = DecomposePrefix(dataBytesAux);
dataBytes = new byte[dataBytesAux.Length - prefix.BytesLength];
Buffer.BlockCopy(dataBytesAux, prefix.BytesLength, dataBytes, 0, dataBytes.Length);
for (int i = 0, j = 0; i < dataBytes.Length; i += (this.KeyLength / 4), j++)
{
int offset = 0;
byte[] buffer = new byte[this.KeyLength / 4];
Tuple <int, int> indexOffsetTuple = prefix.PaddingIndexes.Where(x => x.Item1 == j).FirstOrDefault();
if (indexOffsetTuple != null)
{
offset = indexOffsetTuple.Item2;
}
Buffer.BlockCopy(dataBytes, i, buffer, 0, buffer.Length);
BigInteger decryptedByte = BigInteger.ModPow(new BigInteger(buffer.Skip(offset).ToArray()), this.D, this.N);
decryptedData.AddRange(decryptedByte.ToByteArray());
}
return(Encoding.UTF8.GetString(decryptedData.ToArray()));
}
