/// <summary>
/// Number of samples must be greater than 8 * Number_of_secret_bytes + 32 for LSB without indexes.
/// If this system have specified indexes, then number of samples cannot be less than maximum value from indexes array.
/// </summary>
/// <param name="af"></param>
/// <param name="secret"></param>
/// <returns></returns>
protected override bool CheckContainerCapacity(AudioFile af, byte[] secret)
{
if (Indexes == null)
return (af.Header.NumSamples / 8 - 32)>= secret.Length;
else
{
int max = af.Header.NumSamples;
var test = Indexes.Where(x => x > max);
return test.Count() == 0;
}
}
protected abstract bool CheckContainerCapacity(AudioFile af, byte[] secret);
protected byte[] Extract(AudioFile af)
{
Header hdr = af.Header;
int sampleSize = hdr.BlockAlign;
int start = af.DataStartIndex + sampleSize - 1;
if (Indexes == null)
{
int stop = af.Data.Length;
int dataIndex = start;
//odkoduj długość danych do ukrycia
byte[] lArr = new byte[4];
for (byte i = 0; i < 4; ++i)
{
for (byte idx = 0; idx < 8; ++idx)
{
//przypisz
byte lsb = (byte)(af.Data[dataIndex] % 2);
lArr[i] += (byte)(lsb << idx);
//przesun
dataIndex += sampleSize;
}
}
int secretLenght = BitConverter.ToInt32(lArr, 0);
byte[] secret = new byte[secretLenght];
for (int i = 0; i < secretLenght; ++i)
{
for (byte idx = 0; idx < 8; ++idx)
{
//przypisz
byte lsb = (byte)(af.Data[dataIndex] % 2);
secret[i] += (byte)(lsb << idx);
//przesun
dataIndex += sampleSize;
}
}
return secret;
}
else
{
int nr = 0;
int secretLength = Indexes.Length / 8;
byte[] secret = new byte[secretLength];
int dataIndex;
for (int i = 0; i < secretLength; ++i)
{
for (byte idx = 0; idx < 8; ++idx)
{
//ustaw index
dataIndex = start + sampleSize * Indexes[nr++];
//przypisz
byte lsb = (byte)(af.Data[dataIndex] % 2);
secret[i] += (byte)(lsb << idx);
}
}
return secret;
}
}
protected void Hide(AudioFile af, byte[] secret)
{
if (Indexes == null)
{
Header hdr = af.Header;
int step = hdr.BlockAlign;
int start = af.DataStartIndex + step - 1;
int stop = af.Data.Length;
int dataIndex = start;
//zakoduj długość danych do ukrycia
int secretLength = secret.Length;
var lArr = BitConverter.GetBytes(secretLength);
foreach (byte lghByte in lArr)
{
for (byte bitIndex = 0; bitIndex < 8; ++bitIndex)
{
//przypisz
if (((lghByte >> bitIndex) & 1) == 0)
{
if (af.Data[dataIndex] % 2 == 1)
af.Data[dataIndex] -= 1;
}
else
{
if (af.Data[dataIndex] % 2 == 0)
af.Data[dataIndex] += 1;
}
//przesun
dataIndex += step;
}
}
//w każdej kolejnej próbce umieszczamy po kolejnym bicie sekretu, począwszy od najmłodszego
foreach (byte srtByte in secret)
{
for (byte bitIndex = 0; bitIndex < 8; ++bitIndex)
{
//przypisz
if ((srtByte >> bitIndex) % 2 == 0)
{
if (af.Data[dataIndex] % 2 == 1)
af.Data[dataIndex] -= 1;
}
else
{
if (af.Data[dataIndex] % 2 == 0)
af.Data[dataIndex] += 1;
}
//przesun
dataIndex += step;
}
}
}
else
{
Header hdr = af.Header;
int sampleSize = hdr.BlockAlign;
int start = af.DataStartIndex + sampleSize - 1;
int nr = 0;
int dataIndex;
foreach (byte srtByte in secret)
{
for (byte bitIndex = 0; bitIndex < 8; ++bitIndex)
{
//ustaw index
dataIndex = start + sampleSize * Indexes[nr++];
//przypisz
if ((srtByte >> bitIndex) % 2 == 0)
{
if (af.Data[dataIndex] % 2 == 1)
af.Data[dataIndex] -= 1;
}
else
{
if (af.Data[dataIndex] % 2 == 0)
af.Data[dataIndex] += 1;
}
}
}
}
}
