/// <summary>
/// Build packet binary data
/// </summary>
/// <returns>a byte buffer</returns>
private ByteBuffer BuildImage()
{
ByteBuffer image = _imageBuffer.Value;
image.Clear();
int packetLength = _payload.Length + 5; //type and CRC
int paddingLength = 8 - (packetLength % 8);
image.WriteInt32(packetLength);
image.WriteSecureRandomBytes(paddingLength);
image.WriteByte((byte)_type);
if (_payload.Length > 0)
{
image.Append(_payload);
}
uint crc = CRC.Calc(
image.RawBuffer,
image.RawBufferOffset + PACKET_LENGTH_FIELD_LEN,
image.Length - PACKET_LENGTH_FIELD_LEN);
image.WriteUInt32(crc);
return(image);
}
private byte[] BuildImage()
{
int packet_length = (_data == null ? 0 : _data.Length) + 5; //type and CRC
int padding_length = 8 - (packet_length % 8);
byte[] image = new byte[packet_length + padding_length + 4];
SSHUtil.WriteIntToByteArray(image, 0, packet_length);
for (int i = 0; i < padding_length; i++)
{
image[4 + i] = 0; //padding: filling by random values is better
}
image[4 + padding_length] = _type;
if (_data != null)
{
Array.Copy(_data, 0, image, 4 + padding_length + 1, _data.Length);
}
_CRC = CRC.Calc(image, 4, image.Length - 8);
SSHUtil.WriteIntToByteArray(image, image.Length - 4, (int)_CRC);
return(image);
}
/// <summary>
/// Extracts SSH packet from the internal buffer.
/// </summary>
/// <returns>
/// true if one SSH packet has been extracted.
/// in this case, _packetImage contains Packet Type field and Data field of the SSH packet.
/// </returns>
private bool ConstructPacket()
{
const int PACKET_LENGTH_FIELD_LEN = 4;
const int CHECK_BYTES_FIELD_LEN = 4;
if (_packetLength < 0)
{
if (_inputBuffer.Length < PACKET_LENGTH_FIELD_LEN)
{
return(false);
}
uint packetLength = SSHUtil.ReadUInt32(_inputBuffer.RawBuffer, _inputBuffer.RawBufferOffset);
_inputBuffer.RemoveHead(PACKET_LENGTH_FIELD_LEN);
if (packetLength < MIN_PACKET_LENGTH || packetLength > MAX_PACKET_LENGTH)
{
throw new SSHException(String.Format("invalid packet length : {0}", packetLength));
}
_packetLength = (int)packetLength;
}
int paddingLength = 8 - (_packetLength % 8);
int requiredLength = paddingLength + _packetLength;
if (_inputBuffer.Length < requiredLength)
{
return(false);
}
_packetImage.Clear();
_packetImage.Append(_inputBuffer, 0, requiredLength); // Padding, Packet Type, Data, and Check fields
_inputBuffer.RemoveHead(requiredLength);
if (_cipher != null)
{
_cipher.Decrypt(
_packetImage.RawBuffer, _packetImage.RawBufferOffset, requiredLength,
_packetImage.RawBuffer, _packetImage.RawBufferOffset);
}
if (_checkMAC)
{
uint crc = CRC.Calc(
_packetImage.RawBuffer,
_packetImage.RawBufferOffset,
requiredLength - CHECK_BYTES_FIELD_LEN);
uint expected = SSHUtil.ReadUInt32(
_packetImage.RawBuffer,
_packetImage.RawBufferOffset + requiredLength - CHECK_BYTES_FIELD_LEN);
if (crc != expected)
{
throw new SSHException("CRC Error");
}
}
// retain only Packet Type and Data fields
_packetImage.RemoveHead(paddingLength);
_packetImage.RemoveTail(CHECK_BYTES_FIELD_LEN);
// sanity check
if (_packetImage.Length != _packetLength - CHECK_BYTES_FIELD_LEN)
{
throw new InvalidOperationException();
}
// prepare for the next packet
_packetLength = -1;
return(true);
}