/// <summary>
/// Creates a new stream
/// </summary>
/// <param name="baseStream">The base stream</param>
/// <param name="key">The decryption key</param>
/// <param name="offset">Offset to start at in the input stream</param>
/// <param name="length">The length of the created stream</param>
/// <param name="counterOffset">Offset to add to the counter</param>
/// <param name="ctrHi">The value of the upper 64 bits of the counter</param>
public Aes128CtrStream(Stream baseStream, byte[] key, long offset, long length, long counterOffset, byte[] ctrHi = null)
: base(baseStream, BlockSize, CryptChunkSize / BlockSize, offset)
{
var initialCounter = new byte[BlockSize];
if (ctrHi != null)
{
Array.Copy(ctrHi, initialCounter, 8);
}
_counterOffset = counterOffset;
Length = length;
_tempBuffer = new byte[CryptChunkSize];
_decryptor = new Aes128CtrTransform(key, initialCounter, CryptChunkSize);
Counter = _decryptor.Counter;
UpdateCounter(_counterOffset + base.Position);
baseStream.Position = offset;
}
/// <summary>
/// Creates a new stream
/// </summary>
/// <param name="baseStream">The base stream</param>
/// <param name="key">The decryption key</param>
/// <param name="offset">Offset to start at in the input stream</param>
/// <param name="length">The length of the created stream</param>
/// <param name="counter">The initial counter</param>
public Aes128CtrStream(Stream baseStream, byte[] key, long offset, long length, byte[] counter)
: base(baseStream, BlockSize, 1, offset)
{
_counterOffset = 0;
// Make the stream seekable by remembering the initial counter value
if (counter != null)
{
for (int i = 0; i < 8; i++)
{
_counterOffset |= (long)counter[0xF - i] << (4 + i * 8);
}
}
Length = length;
_tempBuffer = new byte[CryptChunkSize];
_decryptor = new Aes128CtrTransform(key, counter ?? new byte[0x10], CryptChunkSize);
Counter = _decryptor.Counter;
}