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**vngx-jsch** (beta) is an updated version of the popular JSch SSH library
written in pure Java. It has been updated to Java 6 with all the latest
language features and improved code clarity.
/*
* Copyright (c) 2010-2011 Michael Laudati, N1 Concepts LLC.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. The names of the authors may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL N1
* CONCEPTS LLC OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.vngx.jsch;
import static org.vngx.jsch.constants.TransportLayerProtocol.*;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import org.vngx.jsch.algorithm.AlgorithmManager;
import org.vngx.jsch.algorithm.Algorithms;
import org.vngx.jsch.algorithm.Compression;
import org.vngx.jsch.algorithm.Random;
import org.vngx.jsch.cipher.Cipher;
import org.vngx.jsch.cipher.CipherManager;
import org.vngx.jsch.config.SessionConfig;
import org.vngx.jsch.exception.JSchException;
import org.vngx.jsch.hash.Hash;
import org.vngx.jsch.hash.HashManager;
import org.vngx.jsch.hash.MAC;
import org.vngx.jsch.hash.MACException;
import org.vngx.jsch.kex.KexProposal;
import org.vngx.jsch.kex.KeyExchange;
/**
* Implementation to manage the transport layer for {@code Session} to read and
* write SSH packets to/from the socket.
*
* @author Michael Laudati
*/
final class SessionIO {
/** Minimum read size in bytes. (8 bytes) */
private final static int MIN_READ_SIZE = 8;
/** Session instance this IO belongs to. */
private final Session _session;
/** Random instance for generating the random padding in outbound packets. */
private final Random _random;
/** Socket input stream for session's transport layer. */
private final InputStream _sessionIn;
/** Socket output stream for session's transport layer. */
private final OutputStream _sessionOut;
/** Cipher instance for decrypting inbound data from server to client. */
private Cipher _readCipher;
/** Cipher instance for encrypting outbound data from client to server. */
private Cipher _writeCipher;
/** MAC for generating MACs to validate data sent from server to client. */
private MAC _readMac;
/** MAC for generating MACs to send to server from client for validation. */
private MAC _writeMac;
/** Deflater for compressing outbound data (when compression is used). */
private Compression _compressor;
/** Inflater for decompressing inbound data (when compression is used). */
private Compression _decompressor;
/** Current sequence number of inbound packet used for validating s2c MAC. */
private int _inSequence = 0;
/** Current sequence number of outbound packet used for generating c2s MAC. */
private int _outSequence = 0;
/** Result of server-to-client MAC generated by client to compare to server. */
private byte[] _clientMacDigest;
/** Result of server-to-client MAC retrieved from server packet to compare to client. */
private byte[] _serverMacDigest;
/** Server to client cipher IV size. */
private int _readCipherSize = MIN_READ_SIZE;
/** Client to server cipher IV size. */
private int _writeCipherSize = MIN_READ_SIZE;
/** Local buffer to retrieve uncompressed length when compression is used. */
private final int[] _uncompressLen = new int[1];
/**
* Creates a new instance of SessionIO for the specified
* in and out streams for session.
*
* @param session instance
* @param in stream of session socket
* @param out stream of session socket
*/
private SessionIO(Session session, InputStream in, OutputStream out) throws JSchException {
if( session == null ) {
throw new IllegalArgumentException("Session cannot be null");
} else if( in == null ) {
throw new IllegalArgumentException("InputStream cannot be null");
} else if( out == null ) {
throw new IllegalArgumentException("OutputStream cannot be null");
}
_session = session;
_sessionIn = in;
_sessionOut = out;
_random = AlgorithmManager.getManager().createAlgorithm(Algorithms.RANDOM, _session);
}
static SessionIO createIO(Session session, InputStream in, OutputStream out) throws JSchException {
return new SessionIO(session, in, out);
}
public Buffer read(final Buffer buffer) throws JSchException, IOException {
// Reset specified buffer and read in the first block of data.
// Implementations should decrypt the length after receiving the first 8
// (or cipher block size, whichever is larger) bytes of a packet.
buffer.reset();
final int read = getByte(buffer, Math.max(MIN_READ_SIZE, _readCipherSize));
if( _readCipher != null ) {
_readCipher.update(buffer.buffer, 0, read, buffer.buffer, 0);
}
// Read total length of the SSH packet to determine how much to read in
// RFC 4253 6.1 Maximum Packet Length - Throw exception if invalid size.
// Implementations should check that the packet length is reasonable in
// order for the implementation to avoid denial of service and/or buffer
// overflow attacks.
final int packetLen = buffer.getInt();
if( packetLen < 5 || packetLen > Packet.MAX_SIZE ) {
startDiscard(buffer, packetLen, Packet.MAX_SIZE, packetLen < 16 ? "too small" : "too big", SSH_DISCONNECT_PROTOCOL_ERROR);
}
// Determine required space needed to read in remaining packet data and
// ensure it's a multiple of cipher size (otherwise it's corrupt)
// packet length + 4 bytes (packet length) - size already read
final int remaining = packetLen + 4 - read;
if( remaining % Math.max(MIN_READ_SIZE, _readCipherSize) != 0 ) {
startDiscard(buffer, packetLen, Packet.MAX_SIZE - _readCipherSize, "invalid size", SSH_DISCONNECT_PROTOCOL_ERROR);
}
// Read in rest of inbound packet from the input stream
if( remaining > 0 ) {
buffer.ensureCapacity(remaining); // Always ensure buffer capacity
getByte(buffer, remaining);
if( _readCipher != null ) {
_readCipher.update(buffer.buffer, read, remaining, buffer.buffer, read);
}
}
// Generate MAC for packet data and compare to the MAC found at the end
// of the packet sent from server to verify data integrity
if( _readMac != null ) {
_readMac.update(_inSequence); // MAC calculation includes inbound packet sequence
_readMac.update(buffer.buffer, 0, buffer.index);
_readMac.doFinal(_clientMacDigest, 0);
getByte(_serverMacDigest, 0, _serverMacDigest.length); // Read server sent MAC
if( !Arrays.equals(_clientMacDigest, _serverMacDigest) ) {
if( remaining > Packet.MAX_SIZE ) {
throw new MACException("Inbound packet is corrupt: MAC verification failed");
}
startDiscard(buffer, packetLen, Packet.MAX_SIZE - remaining, "MAC verification failed", SSH_DISCONNECT_MAC_ERROR);
}
}
_inSequence++; // Increment number of inbound packets (required for MAC)
// Decompress the packet data portion if enabled
if( _decompressor != null ) {
int paddingSize = buffer.buffer[4];
_uncompressLen[0] = buffer.index - 5 - paddingSize;
byte[] uncompressed = _decompressor.uncompress(buffer.buffer, 5, _uncompressLen);
if( uncompressed == null ) {
throw new JSchException("Failed to decompress packet data", SSH_DISCONNECT_COMPRESSION_ERROR);
}
buffer.buffer = uncompressed;
buffer.index = 5 + _uncompressLen[0]; // Index is set excluding setPadding
}
buffer.rewind(); // Rewind buffer to prepare for use
return buffer; // and return to caller
}
/**
* Detects an attack on the SSH session during a read operation and throws
* an appropriate exception. The method will always complete with an
* exception being thrown.
*
* @param buffer to read into
* @param packetLength
* @param discard
* @param msg to throw in exception
* @param disconnect reason code to pass to server
* @throws JSchException if any errors occur
* @throws IOException if any IO errors occur
*/
private void startDiscard(Buffer buffer, int packetLength, int discard, String msg, int reasonCode) throws JSchException, IOException {
// If the server-to-client cipher is not using cipher-block chaining mode
// of operation, then the inbound SSH packet is corrupt and session should end
if( !_readCipher.isCBC() ) {
throw new JSchException("Inbound packet is corrupt: "+msg, reasonCode);
}
// Finish reading in the rest of the data from the Session's in stream
// which needs to be discarded.
MAC discardMac = packetLength != Packet.MAX_SIZE ? _readMac : null;
discard -= buffer.index;
while( discard > 0 ) {
buffer.reset();
int len = Math.min(discard, buffer.buffer.length);
getByte(buffer.buffer, 0, len);
if( discardMac != null ) {
discardMac.update(buffer.buffer, 0, len);
}
discard -= len;
}
if( discardMac != null ) {
discardMac.doFinal(buffer.buffer, 0);
}
throw new JSchException("Inbound packet is corrupt: "+msg, reasonCode);
}
/**
* Writes the packet to the outbound socket stream after applying encoding.
* Encoding includes compression, random setPadding, MAC hash, and cipher
* encryption.
*
* @param packet to send
* @throws Exception if any errors occur
*/
void write(final Packet packet) throws JSchException, IOException {
// If compression is enabled, compress the buffer data excluding the
// packet size and setPadding size (first 5 bytes of buffer)
if( _compressor != null ) {
packet.buffer.index = _compressor.compress(packet.buffer.buffer, 5, packet.buffer.index);
}
// Add random padding to end of packet and set packet length and pad length
packet.setPadding(_writeCipher != null ? _writeCipherSize : 8, _random);
// If MAC algorithm is set, add the MAC to end of packet
if( _writeMac != null ) {
_writeMac.update(_outSequence);
_writeMac.update(packet.buffer.buffer, 0, packet.buffer.index);
_writeMac.doFinal(packet.buffer.buffer, packet.buffer.index);
}
// Apply the encryption to the entire packet contents, excluding MAC at end
if( _writeCipher != null ) {
_writeCipher.update(packet.buffer.buffer, 0, packet.buffer.index, packet.buffer.buffer, 0);
}
// Move index to end of MAC (MAC should not have been encrypted)
if( _writeMac != null ) {
packet.buffer.skip(_writeMac.getBlockSize());
}
put(packet); // Send packet data to session output stream
_outSequence++; // Increment outbound sequence after packet's been sent
}
/**
* Reads from the input stream into the specified data buffer.
*
* @param buffer
* @param start
* @param length
* @throws IOException
*/
void getByte(byte[] buffer, int start, int length) throws IOException {
int bytesRead;
do {
if( (bytesRead = _sessionIn.read(buffer, start, length)) < 0 ) {
throw new IOException("End of Session InputStream");
}
start += bytesRead;
length -= bytesRead;
} while( length > 0 );
}
/**
* Reads from the input stream into the specified data buffer.
*
* @param buffer
* @param length
* @throws IOException
*/
int getByte(Buffer buffer, int length) throws IOException {
int bytesRead;
do {
if( (bytesRead = _sessionIn.read(buffer.buffer, buffer.index, length)) < 0 ) {
throw new IOException("End of Session InputStream");
}
buffer.skip(bytesRead); // Update buffer's internal index and
length -= bytesRead; // update amount left to read in and keep
} while( length > 0 ); // looping until finished
return bytesRead; // Return the amount of bytes read in
}
/**
* Writes the specified packet to the output stream.
*
* @param p packet to write
* @throws IOException
*/
void put(Packet p) throws IOException {
_sessionOut.write(p.buffer.buffer, 0, p.buffer.index);
_sessionOut.flush();
}
/**
* Generates new keys during key exchange and sets up the required
* algorithms for the session including ciphers, MACs and compression
* implementations.
*
* @param kex to use for generating key values
* @throws JSchException if any errors occur
*/
void initNewKeys(KeyExchange kex) throws JSchException {
KexProposal proposal = kex.getKexProposal();
Hash hash = kex.getKexAlgorithm().getHash();
byte[] H = kex.getKexAlgorithm().getH();
byte[] K = kex.getKexAlgorithm().getK();
try {
// Initial IV client to server: HASH (K || H || "A" || session_id)
// Initial IV server to client: HASH (K || H || "B" || session_id)
// Encryption key client to server: HASH (K || H || "C" || session_id)
// Encryption key server to client: HASH (K || H || "D" || session_id)
// Integrity key client to server: HASH (K || H || "E" || session_id)
// Integrity key server to client: HASH (K || H || "F" || session_id)
Buffer buffer = new Buffer();
buffer.putMPInt(K);
buffer.putBytes(H);
int letterIndex = buffer.index;
buffer.putByte((byte) 0x41); // 0x41 = 'A'
buffer.putBytes(_session.getSessionId());
hash.update(buffer.buffer, 0, buffer.index);
byte[] c2sCipherIV = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'B'
hash.update(buffer.buffer, 0, buffer.index);
byte[] s2cCipherIV = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'C'
hash.update(buffer.buffer, 0, buffer.index);
byte[] c2sCipherKey = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'D'
hash.update(buffer.buffer, 0, buffer.index);
byte[] s2cCipherKey = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'E'
hash.update(buffer.buffer, 0, buffer.index);
byte[] c2sMacIV = hash.digest();
buffer.buffer[letterIndex]++; // Increment to 'F'
hash.update(buffer.buffer, 0, buffer.index);
byte[] s2cMacIV = hash.digest();
// Generate server-to-client cipher instance
_readCipher = CipherManager.getManager().createCipher(proposal.getCipherAlgStoC(), _session);
while( _readCipher.getBlockSize() > s2cCipherKey.length ) {
buffer.reset();
buffer.skip(letterIndex);
buffer.putBytes(s2cCipherKey);
hash.update(buffer.buffer, 0, buffer.index);
s2cCipherKey = Util.join(s2cCipherKey, hash.digest());
}
_readCipher.init(Cipher.DECRYPT_MODE, s2cCipherKey, s2cCipherIV);
_readCipherSize = _readCipher.getIVSize();
// Generate server-to-client MAC instance
_readMac = HashManager.getManager().createMAC(proposal.getMACAlgStoC());
_readMac.init(s2cMacIV);
_clientMacDigest = new byte[_readMac.getBlockSize()];
_serverMacDigest = new byte[_readMac.getBlockSize()];
// Generate client-to-server cipher instance
_writeCipher = CipherManager.getManager().createCipher(proposal.getCipherAlgCtoS(), _session);
while( _writeCipher.getBlockSize() > c2sCipherKey.length ) {
buffer.reset();
buffer.skip(letterIndex);
buffer.putBytes(c2sCipherKey);
hash.update(buffer.buffer, 0, buffer.index);
c2sCipherKey = Util.join(c2sCipherKey, hash.digest());
}
_writeCipher.init(Cipher.ENCRYPT_MODE, c2sCipherKey, c2sCipherIV);
_writeCipherSize = _writeCipher.getIVSize();
// Generate client-to-server MAC instance
_writeMac = HashManager.getManager().createMAC(proposal.getMACAlgCtoS());
_writeMac.init(c2sMacIV);
// Generate inflater/deflater instances for compression
initCompressor(proposal.getCompressionAlgCtoS());
initDecompressor(proposal.getCompressionAlgStoC());
} catch(Exception e) {
throw new JSchException("Failed to initialize new keys", e);
}
kex.kexCompleted(); // No longer in key exchange
}
/**
* Initializes the Compression instance for deflating
* compressed data sent from client to server. If the compression type is
* 'none', then the deflater instance is set to null.
*
* @param method
* @throws JSchException
*/
void initCompressor(String method) throws JSchException {
if( Compression.COMPRESSION_NONE.equals(method) ) {
_compressor = null;
} else if( Compression.COMPRESSION_ZLIB.equals(method) ||
(_session.isAuthenticated() && Compression.COMPRESSION_ZLIB_OPENSSH.equals(method)) ) {
try {
_compressor = AlgorithmManager.getManager().createAlgorithm(method, _session);
_compressor.init(Compression.COMPRESS_MODE, _session.getConfig().getInteger(SessionConfig.COMPRESSION_LEVEL));
} catch(Exception e) {
throw new JSchException("Failed to initialize deflater, method: "+method, e);
}
}
}
/**
* Initializes the Compression instance for inflating
* compressed data sent from server to client. If the compression type is
* 'none', then the inflater instance is set to null.
*
* @param method of compression ('none', 'zlib', etc)
* @throws JSchException if any errors occur
*/
void initDecompressor(String method) throws JSchException {
if( Compression.COMPRESSION_NONE.equals(method) ) {
_decompressor = null;
} else if( Compression.COMPRESSION_ZLIB.equals(method) ||
(_session.isAuthenticated() && Compression.COMPRESSION_ZLIB_OPENSSH.equals(method)) ) { // why only if authed?
try {
_decompressor = AlgorithmManager.getManager().createAlgorithm(method, _session);
_decompressor.init(Compression.DECOMPRESS_MODE, 0);
} catch(Exception e) {
throw new JSchException("Failed to initialize inflater, method: "+method, e);
}
}
}
int getWriteMacSize() {
return _writeMac != null ? _writeMac.getBlockSize() : 0;
}
}