class Net::SSH::Transport::State

Encapsulates state information about one end of an SSH connection. Such state includes the packet sequence number, the algorithms in use, how many packets and blocks have been processed since the last reset, and so forth. This class will never be instantiated directly, but is used as part of the internal state of the PacketStream module.

Attributes

block_size[R]

The block size for the cipher

blocks[R]

The number of data blocks processed since the last call to reset!

cipher[R]

The cipher algorithm in use for this socket endpoint.

compression[R]

The compression algorithm in use for this endpoint.

compression_level[R]

The compression level to use when compressing data (or nil, for the default).

hmac[R]

The hmac algorithm in use for this endpoint.

max_blocks[RW]

The maximum number of blocks that this endpoint wants to process before needing a rekey.

max_packets[RW]

The maximum number of packets that this endpoint wants to process before needing a rekey.

packets[R]

The number of packets processed since the last call to reset!

rekey_limit[RW]

The user-specified maximum number of bytes that this endpoint ought to process before needing a rekey.

role[R]

The role that this state plays (either :client or :server)

sequence_number[R]

The next packet sequence number for this socket endpoint.

socket[R]

The socket object that owns this state object.

Public Class Methods

new(socket, role) click to toggle source

Creates a new state object, belonging to the given socket. Initializes the algorithms to “none”.

# File lib/net/ssh/transport/state.rb, line 59
def initialize(socket, role)
  @socket = socket
  @role = role
  @sequence_number = @packets = @blocks = 0
  @cipher = CipherFactory.get("none")
  @block_size = 8
  @hmac = HMAC.get("none")
  @compression = nil
  @compressor = @decompressor = nil
  @next_iv = ""
end

Public Instance Methods

cleanup() click to toggle source

Closes any the compressor and/or decompressor objects that have been instantiated.

# File lib/net/ssh/transport/state.rb, line 167
def cleanup
  if @compressor
    @compressor.finish if !@compressor.finished?
    @compressor.close
  end
    
  if @decompressor
    # we call reset here so that we don't get warnings when we try to
    # close the decompressor
    @decompressor.reset
    @decompressor.close
  end
    
  @compressor = @decompressor = nil
end

compress(data) click to toggle source

Compresses the data. If no compression is in effect, this will just return the data unmodified, otherwise it uses compressor to compress the data.

# File lib/net/ssh/transport/state.rb, line 122
def compress(data)
  data = data.to_s
  return data unless compression?
  compressor.deflate(data, Zlib::SYNC_FLUSH)
end

compression?() click to toggle source

Returns true if data compression/decompression is enabled. This will return true if :standard compression is selected, or if :delayed compression is selected and the :authenticated hint has been received by the socket.

# File lib/net/ssh/transport/state.rb, line 116
def compression?
  compression == :standard || (compression == :delayed && socket.hints[:authenticated])
end

compressor() click to toggle source

The compressor object to use when compressing data. This takes into account the desired compression level.

# File lib/net/ssh/transport/state.rb, line 103
def compressor
  @compressor ||= Zlib::Deflate.new(compression_level || Zlib::DEFAULT_COMPRESSION)
end

decompress(data) click to toggle source

Deompresses the data. If no compression is in effect, this will just return the data unmodified, otherwise it uses decompressor to decompress the data.

# File lib/net/ssh/transport/state.rb, line 130
def decompress(data)
  data = data.to_s
  return data unless compression?
  decompressor.inflate(data)
end

decompressor() click to toggle source

The decompressor object to use when decompressing data.

# File lib/net/ssh/transport/state.rb, line 108
def decompressor
  @decompressor ||= Zlib::Inflate.new(nil)
end

final_cipher() click to toggle source

# File lib/net/ssh/transport/state.rb, line 86
def final_cipher
  result = cipher.final
  update_next_iv(role == :client ? result : "", true)
  return result
end

increment(packet_length) click to toggle source

Increments the counters. The sequence number is incremented (and remapped so it always fits in a 32-bit integer). The number of packets and blocks are also incremented.

# File lib/net/ssh/transport/state.rb, line 95
def increment(packet_length)
  @sequence_number = (@sequence_number + 1) & 0xFFFFFFFF
  @packets += 1
  @blocks += (packet_length + 4) / @block_size
end

needs_rekey?() click to toggle source

Returns true if the number of packets processed exceeds the maximum number of packets, or if the number of blocks processed exceeds the maximum number of blocks.

# File lib/net/ssh/transport/state.rb, line 186
def needs_rekey?
  max_packets && packets > max_packets ||
  max_blocks && blocks > max_blocks
end

reset!() click to toggle source

Resets the counters on the state object, but leaves the #sequence_number unchanged. It also sets defaults for and recomputes the #max_packets and #max_blocks values.

# File lib/net/ssh/transport/state.rb, line 139
def reset!
  @packets = @blocks = 0
    
  @max_packets ||= 1 << 31
    
  @block_size = cipher.block_size
    
  if max_blocks.nil?
    # cargo-culted from openssh. the idea is that "the 2^(blocksize*2)
    # limit is too expensive for 3DES, blowfish, etc., so enforce a 1GB
    # limit for small blocksizes."
    if @block_size >= 16
      @max_blocks = 1 << (@block_size * 2)
    else
      @max_blocks = (1 << 30) / @block_size
    end
    
    # if a limit on the # of bytes has been given, convert that into a
    # minimum number of blocks processed.
    
    @max_blocks = [@max_blocks, rekey_limit / @block_size].min if rekey_limit
  end
    
  cleanup
end

set(values) click to toggle source

A convenience method for quickly setting multiple values in a single command.

# File lib/net/ssh/transport/state.rb, line 73
def set(values)
  values.each do |key, value|
    instance_variable_set("@#{key}", value)
  end
  reset!
end

update_cipher(data) click to toggle source

# File lib/net/ssh/transport/state.rb, line 80
def update_cipher(data)
  result = cipher.update(data)
  update_next_iv(role == :client ? result : data)
  return result
end