private void ReadPacketWithDecryptedHead()
{
/* SOURCE : _head(packet_size, padding_length) + _buffer(payload + mac)
* DESTINATION : _packet(payload)
*/
int offset = _buffer.Offset;
int packet_length = SSHUtil.ReadInt32(_head, 0);
if (packet_length <= 0 || packet_length >= MAX_PACKET_LENGTH)
{
throw new SSHException(String.Format("packet size {0} is invalid", packet_length));
}
_packet.AssureCapacity(packet_length + PACKET_LENGTH_FIELD_LEN + SEQUENCE_FIELD_LEN);
int padding_length = (int)_head[PACKET_LENGTH_FIELD_LEN];
if (padding_length < 4)
{
throw new SSHException("padding length is invalid");
}
//to compute hash, we write _sequence at the top of _packet.Data
SSHUtil.WriteIntToByteArray(_packet.Data, 0, _sequence);
Array.Copy(_head, 0, _packet.Data, SEQUENCE_FIELD_LEN, _head.Length);
if (packet_length > (_cipher.BlockSize - PACKET_LENGTH_FIELD_LEN)) //in case of _head is NOT the entire of the packet
{
int decrypting_size = packet_length - (_cipher.BlockSize - PACKET_LENGTH_FIELD_LEN);
_cipher.Decrypt(_buffer.Data, _buffer.Offset, decrypting_size, _packet.Data, SEQUENCE_FIELD_LEN + _head.Length);
}
_packet.SetLength(SEQUENCE_FIELD_LEN + PACKET_LENGTH_FIELD_LEN + PADDING_LENGTH_FIELD_LEN, packet_length - 1 - padding_length);
_buffer.Consume(packet_length + PACKET_LENGTH_FIELD_LEN - _head.Length + _mac.Size);
if (_macEnabled)
{
byte[] result = _mac.ComputeHash(_packet.Data, 0, 4 + PACKET_LENGTH_FIELD_LEN + packet_length);
if (SSHUtil.memcmp(result, 0, _buffer.Data, _buffer.Offset - _mac.Size, _mac.Size) != 0)
{
throw new SSHException("MAC mismatch");
}
}
}
