public static string CreateOTP(YubikeySettings key, Form1 form)
{
string tokenID = ModHex.Encode(key.TokenID);
// Assemble key unencrypted data
byte[] keyBytes = new byte[16];
for (int i = 0; i < key.PrivateID.Length; ++i)
{
keyBytes[i] = key.PrivateID[i];
}
keyBytes[6] = (byte)(key.SessionCounter & 0xff);
keyBytes[7] = (byte)((key.SessionCounter >> 8) & 0xff);
form.SessionCounter = key.SessionCounter.ToString();
TimeSpan diff = DateTime.Now - key.StartTime;
int timer = (int)((((uint)(diff.TotalSeconds / TS_SEC) & 0x00FFFFFF) + key.TimeStamp) & 0x00FFFFFF);
form.Timestamp = timer.ToString();
keyBytes[8] = (byte)(timer & 0xff);
keyBytes[9] = (byte)((timer >> 8) & 0xff);
keyBytes[10] = (byte)((timer >> 16) & 0xff);
keyBytes[11] = key.UseCounter++;
form.UseCounter = keyBytes[11].ToString();
byte[] buffer = new byte[2];
RNGCryptoServiceProvider.Create().GetBytes(buffer);
form.Random = (((int)buffer[1] << 8) + (int)buffer[0]).ToString();
keyBytes[12] = buffer[0];
keyBytes[13] = buffer[1];
CRC(keyBytes);
using (Rijndael aes = Rijndael.Create())
{
aes.Padding = PaddingMode.None;
aes.Mode = CipherMode.ECB;
using (ICryptoTransform xform = aes.CreateEncryptor(key.Secret, new byte[16]))
{
byte[] plainBytes = new byte[16];
xform.TransformBlock(keyBytes, 0, keyBytes.Length, plainBytes, 0);
string otp = tokenID + ModHex.Encode(plainBytes);
return(otp);
}
}
}
public static string ModHexString(byte[] input)
{
return(ModHex.Encode(input));
}