I'm having problems with an algorithm I'm doing to decrypt data. The is problems every time that I try to run an overflow error happened in line:
uint sum=(numberOfRounds*Delta);
The file I'm reading just has the array in hexadecimal: 3D 00 01 12 02 CC F8 FD 33 3B 44 01 00 92 00 03 03 00 CB 44 6D 38 01 12 00 24 D6 23 02 04 E9 65 F7 44 00 00 00 00 00 5B D2 D6 ED 3A 81 03 DD 00 00 00 00 00 00 AC 87 B0 51 0F 27 01 00 D9
The code is bellow:
private const int EncryptedDataBlockSizeInBytes = 4;
private static readonly uint[] Key = new uint[] { 0xA50DADD1, 0xFEAD1276, 0x03948029, 0x49493095 };
private const uint Delta = 0x9E3779B9;
public static int headersize = 13;
public static int crcsize = 1;
public static byte[] Decrypt(byte[] data, int offset, int count, uint[] key)
{
if (count % EncryptedDataBlockSizeInBytes != 0)
{
throw new ArgumentException("The count of the data to be decrypted must be divisible by 4.");
}
// Convert the byte array into a uint array
uint[] dataInUints = ConvertBytesToUints(data, offset, count);
uint numberOfRounds = (uint)(6 + (52 / dataInUints.Length));
uint n = (uint)(dataInUints.Length - 1);
uint sum = numberOfRounds * Delta;
uint y = dataInUints[0];
do
{
uint e = (sum >> 2) & 3;
uint z;
for (uint i = n; i > 0; i--)
{
z = dataInUints[i - 1];
dataInUints[i] -= XxteaMx(z, y, e, sum, key, i);
y = dataInUints[i];
}
z = dataInUints[n];
dataInUints[0] -= XxteaMx(z, y, e, sum, key, 0);
y = dataInUints[0];
sum -= Delta;
}
while (sum != 0);
// Convert the decrypted data back into a byte array and return the result
return ConvertUintsToBytes(dataInUints);
}
private static uint XxteaMx(uint z, uint y, uint e, uint sum, uint[] key, uint i)
{
return (((((z) >> 5) ^ ((y) << 2)) + (((y) >> 3) ^ ((z) << 4))) ^ (((sum) ^ y) + ((key)[((i) & 3U) ^ (e)] ^ (z))));
}
private static uint[] ConvertBytesToUints(byte[] data, int offset, int count)
{
uint[] result = new uint[count / 4];
// Run through the data and create the uints from
// the array of bytes
for (int i = offset, j = 0; i < offset + count; i += 4, j++)
{
result[j] = ((uint)data[i + 3] << 24) | ((uint)data[i + 2] << 16) | ((uint)data[i + 1] << 8) | (data[i]);
}
// Return the array of uints
return result;
}
private static byte[] ConvertUintsToBytes(uint[] data)
{
byte[] result = new byte[data.Length * 4];
// Run through the data and create the bytes from
// the array of uints
for (int i = 0, j = 0; i < data.Length; i++, j += 4)
{
result[j] = (byte)(data[i]);
result[j + 1] = (byte)(data[i] >> 8);
result[j + 2] = (byte)(data[i] >> 16);
result[j + 3] = (byte)(data[i] >> 24);
}
// Return the array of bytes
return result;
}
void Button1Click(object sender, EventArgs e)
{
FileStream file = new FileStream("arquivobin.dat", FileMode.Open);
BinaryReader br = new BinaryReader(file);
byte[] data = new byte[br.BaseStream.Length];
data = br.ReadBytes((int)br.BaseStream.Length);
string s = "";
richTextBox1.Text = "My binary file data:" + "\n";
for(int i =0; i< data.Length; i++){
s = data[i].ToString();
richTextBox1.Text += s + " ";
}
richTextBox1.Text += "\n\n\n" ;
richTextBox1.Text += "My HEADER:" + "\n";
for (int i = 0; i < headersize; i++)
{
s = data[i].ToString();
richTextBox1.Text += s + " ";
}
richTextBox1.Text += "\n\n\n";
richTextBox1.Text += "My payload:" + "\n";
for(int i = headersize; i < data.Length - crcsize; i++){
s = data[i].ToString();
richTextBox1.Text += s + " ";
}
richTextBox1.Text += "\n\n\n";
richTextBox1.Text += "My CheckSum:" + "\n";
s = printhex(data[data.Length - crcsize]);
richTextBox1.Text += s;
int offset = headersize;
int count = data.Length - crcsize - headersize;
byte[] result = Decrypt(data, headersize, count, Key);
richTextBox1.Text += "\n\n\n";
richTextBox1.Text += "My Decrypted:" + "\n";
for (int i = headersize; i < data.Length - crcsize; i++)
{
s = result[i].ToString();
richTextBox1.Text += s + " ";
}
file.Close();
}
}
