/// <summary>
/// Extracts SSH packet from the internal buffer.
/// </summary>
/// <returns>
/// true if one SSH packet has been extracted.
/// in this case, _packetImage contains payload part of the SSH packet.
/// </returns>
private bool ConstructPacket()
{
const int SEQUENCE_NUMBER_FIELD_LEN = 4;
const int PACKET_LENGTH_FIELD_LEN = 4;
const int PADDING_LENGTH_FIELD_LEN = 1;
lock (_cipherSync) {
if (_packetLength < 0)
{
int headLen = (_cipher != null) ? _cipher.BlockSize : 4;
if (_inputBuffer.Length < headLen)
{
return(false);
}
_packetImage.Clear();
_packetImage.WriteUInt32(_sequence);
_packetImage.Append(_inputBuffer, 0, headLen);
_inputBuffer.RemoveHead(headLen);
int headOffset = _packetImage.RawBufferOffset + SEQUENCE_NUMBER_FIELD_LEN;
if (_cipher != null)
{
// decrypt first block
_cipher.Decrypt(
_packetImage.RawBuffer, headOffset, headLen,
_packetImage.RawBuffer, headOffset);
}
uint packetLength = SSHUtil.ReadUInt32(_packetImage.RawBuffer, headOffset);
if (packetLength < MIN_PACKET_LENGTH || packetLength >= MAX_PACKET_LENGTH)
{
throw new SSHException(String.Format("invalid packet length : {0}", packetLength));
}
_packetLength = (int)packetLength;
}
int packetHeadLen = _packetImage.Length; // size already read in
int requiredLength = SEQUENCE_NUMBER_FIELD_LEN + PACKET_LENGTH_FIELD_LEN + _packetLength + _macLength - packetHeadLen;
if (_inputBuffer.Length < requiredLength)
{
return(false);
}
_packetImage.Append(_inputBuffer, 0, requiredLength);
_inputBuffer.RemoveHead(requiredLength);
if (_cipher != null)
{
// decrypt excluding MAC
int headOffset = _packetImage.RawBufferOffset + packetHeadLen;
_cipher.Decrypt(
_packetImage.RawBuffer, headOffset, requiredLength - _macLength,
_packetImage.RawBuffer, headOffset);
}
int paddingLength = _packetImage[SEQUENCE_NUMBER_FIELD_LEN + PACKET_LENGTH_FIELD_LEN];
if (paddingLength < 4)
{
throw new SSHException(String.Format("invalid padding length : {0}", paddingLength));
}
int payloadLength = _packetLength - PADDING_LENGTH_FIELD_LEN - paddingLength;
if (_checkMAC && _mac != null)
{
int contentLen = SEQUENCE_NUMBER_FIELD_LEN + PACKET_LENGTH_FIELD_LEN + _packetLength;
byte[] result = _mac.ComputeHash(_packetImage.RawBuffer, _packetImage.RawBufferOffset, contentLen);
if (result.Length != _macLength ||
!SSHUtil.ByteArrayEqual(result, 0, _packetImage.RawBuffer, _packetImage.RawBufferOffset + contentLen, _macLength))
{
throw new SSHException("MAC mismatch");
}
}
// retain only payload
_packetImage.RemoveHead(SEQUENCE_NUMBER_FIELD_LEN + PACKET_LENGTH_FIELD_LEN + PADDING_LENGTH_FIELD_LEN);
_packetImage.RemoveTail(_macLength + paddingLength);
// sanity check
if (_packetImage.Length != payloadLength)
{
throw new InvalidOperationException();
}
// prepare for the next packet
++_sequence;
_packetLength = -1;
return(true);
}
}
// Derived class can override this method to modify the buffer.
public virtual DataFragment Close(Cipher cipher, MAC mac, int sequence)
{
if (!_isOpen)
throw new SSHException("internal state error");
int blocksize = cipher == null ? 8 : cipher.BlockSize;
int payloadLength = _writer.Length - (SEQUENCE_MARGIN + LENGTH_MARGIN + PADDING_MARGIN);
int paddingLength = 11 - payloadLength % blocksize;
while (paddingLength < 4)
paddingLength += blocksize;
int packetLength = PADDING_MARGIN + payloadLength + paddingLength;
int imageLength = packetLength + LENGTH_MARGIN;
//fill padding
byte[] tmp = new byte[4];
Rng rng = RngManager.GetSecureRng();
for (int i = 0; i < paddingLength; i += 4) {
rng.GetBytes(tmp);
_writer.Write(tmp);
}
//manipulate stream
byte[] rawbuf = _writer.UnderlyingBuffer;
SSHUtil.WriteIntToByteArray(rawbuf, 0, sequence);
SSHUtil.WriteIntToByteArray(rawbuf, SEQUENCE_MARGIN, packetLength);
rawbuf[SEQUENCE_MARGIN + LENGTH_MARGIN] = (byte)paddingLength;
//mac
if (mac != null) {
byte[] macCode = mac.ComputeHash(rawbuf, 0, packetLength + LENGTH_MARGIN + SEQUENCE_MARGIN);
Array.Copy(macCode, 0, rawbuf, packetLength + LENGTH_MARGIN + SEQUENCE_MARGIN, macCode.Length);
imageLength += macCode.Length;
}
//encrypt
if (cipher != null)
cipher.Encrypt(rawbuf, SEQUENCE_MARGIN, packetLength + LENGTH_MARGIN, rawbuf, SEQUENCE_MARGIN);
_dataFragment.Init(rawbuf, SEQUENCE_MARGIN, imageLength);
_isOpen = false;
return _dataFragment;
}
public void Close(Cipher cipher, Random rnd, MAC mac, int sequence, DataFragment result)
{
if(!_is_open) throw new SSHException("internal state error");
int blocksize = cipher==null? 8 : cipher.BlockSize;
int payload_length = _writer.Length - (SEQUENCE_MARGIN + LENGTH_MARGIN + PADDING_MARGIN);
int r = 11 - payload_length % blocksize;
while(r < 4) r += blocksize;
_paddingLength = r;
_packetLength = PADDING_MARGIN + payload_length + _paddingLength;
int image_length = _packetLength + LENGTH_MARGIN;
//fill padding
for(int i=0; i<_paddingLength; i+=4)
_writer.Write(rnd.Next());
//manipulate stream
byte[] rawbuf = _writer.UnderlyingBuffer;
SSHUtil.WriteIntToByteArray(rawbuf, 0, sequence);
SSHUtil.WriteIntToByteArray(rawbuf, SEQUENCE_MARGIN, _packetLength);
rawbuf[SEQUENCE_MARGIN + LENGTH_MARGIN] = (byte)_paddingLength;
//mac
if(mac!=null) {
_mac = mac.ComputeHash(rawbuf, 0, _packetLength+LENGTH_MARGIN+SEQUENCE_MARGIN);
Array.Copy(_mac, 0, rawbuf, _packetLength+LENGTH_MARGIN+SEQUENCE_MARGIN, _mac.Length);
image_length += _mac.Length;
}
//encrypt
if(cipher!=null)
cipher.Encrypt(rawbuf, SEQUENCE_MARGIN, _packetLength+LENGTH_MARGIN, rawbuf, SEQUENCE_MARGIN);
result.Init(rawbuf, SEQUENCE_MARGIN, image_length);
_is_open = false;
}