class Net::SSH::Transport::Algorithms

  1. lib/net/ssh/transport/algorithms.rb
Parent: Transport

Implements the higher-level logic behind an SSH key-exchange. It handles both the initial exchange, as well as subsequent re-exchanges (as needed). It also encapsulates the negotiation of the algorithms, and provides a single point of access to the negotiated algorithms.

You will never instantiate or reference this directly. It is used internally by the transport layer.

Included modules

  1. Constants
  2. Loggable

Constants

ALGORITHMS = { :host_key => %w(ssh-rsa ssh-dss ssh-rsa-cert-v01@openssh.com ssh-rsa-cert-v00@openssh.com), :kex => %w(diffie-hellman-group-exchange-sha1 diffie-hellman-group1-sha1 diffie-hellman-group14-sha1 diffie-hellman-group-exchange-sha256), :encryption => %w(aes128-cbc 3des-cbc blowfish-cbc cast128-cbc aes192-cbc aes256-cbc rijndael-cbc@lysator.liu.se idea-cbc none arcfour128 arcfour256 arcfour aes128-ctr aes192-ctr aes256-ctr camellia128-cbc camellia192-cbc camellia256-cbc camellia128-cbc@openssh.org camellia192-cbc@openssh.org camellia256-cbc@openssh.org camellia128-ctr camellia192-ctr camellia256-ctr camellia128-ctr@openssh.org camellia192-ctr@openssh.org camellia256-ctr@openssh.org cast128-ctr blowfish-ctr 3des-ctr aes256-gcm@openssh.com aes128-gcm@openssh.com ), :hmac => %w(hmac-sha1 hmac-md5 hmac-sha1-96 hmac-md5-96 hmac-ripemd160 hmac-ripemd160@openssh.com hmac-sha2-256 hmac-sha2-512 hmac-sha2-256-96 hmac-sha2-512-96 none hmac-sha2-512-etm@openssh.com hmac-sha2-256-etm@openssh.com umac-128-etm@openssh.com), :compression => %w(none zlib@openssh.com zlib), :language => %w() }  

Define the default algorithms, in order of preference, supported by Net::SSH.

Attributes

algorithms [R]

The hash of algorithms preferred by the client, which will be told to the server during algorithm negotiation.
compression_client [R]

The type of compression to use to compress packets being sent by the client.
compression_server [R]

The type of compression to use to decompress packets arriving from the server.
encryption_client [R]

The type of the cipher to use to encrypt packets sent from the client to the server.
encryption_server [R]

The type of the cipher to use to decrypt packets arriving from the server.
hmac_client [R]

The type of HMAC to use to sign packets sent by the client.
hmac_server [R]

The type of HMAC to use to validate packets arriving from the server.
host_key [R]

The type of host key that will be used for this session.
kex [R]

The kex algorithm to use settled on between the client and server.
language_client [R]

The language that will be used in messages sent by the client.
language_server [R]

The language that will be used in messages sent from the server.
options [R]

The hash of options used to initialize this object
session [R]

The underlying transport layer session that supports this object
session_id [R]

The session-id for this session, as decided during the initial key exchange.

Public Class methods

allowed_packet? (packet)

Returns true if the given packet can be processed during a key-exchange.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 114
def self.allowed_packet?(packet)
  ( 1.. 4).include?(packet.type) ||
  ( 6..19).include?(packet.type) ||
  (21..49).include?(packet.type)
end
new (session, options={})

Instantiates a new Algorithms object, and prepares the hash of preferred algorithms based on the options parameter and the ALGORITHMS constant.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 122
def initialize(session, options={})
  @session = session
  @logger = session.logger
  @options = options
  @algorithms = {}
  @pending = @initialized = false
  @client_packet = @server_packet = nil
  prepare_preferred_algorithms!
end

Public Instance methods

[] (key)

A convenience method for accessing the list of preferred types for a specific algorithm (see algorithms).

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 159
def [](key)
  algorithms[key]
end
accept_kexinit (packet)

Called by the transport layer when a KEXINIT packet is recieved, indicating that the server wants to exchange keys. This can be spontaneous, or it can be in response to a client-initiated rekey request (see rekey!). Either way, this will block until the key exchange completes.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 146
def accept_kexinit(packet)
  info { "got KEXINIT from server" }
  @server_data = parse_server_algorithm_packet(packet)
  @server_packet = @server_data[:raw]
  if !pending?
    send_kexinit
  else
    proceed!
  end
end
allow? (packet)

Returns true if no exchange is pending, and otherwise returns true or false depending on whether the given packet is of a type that is allowed during a key exchange.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 175
def allow?(packet)
  !pending? || Algorithms.allowed_packet?(packet)
end
initialized? ()

Returns true if the algorithms have been negotiated at all.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 180
def initialized?
  @initialized
end
pending? ()

Returns true if a key-exchange is pending. This will be true from the moment either the client or server requests the key exchange, until the exchange completes. While an exchange is pending, only a limited number of packets are allowed, so event processing essentially stops during this period.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 168
def pending?
  @pending
end
rekey! ()

Request a rekey operation. This will return immediately, and does not actually perform the rekey operation. It does cause the session to change state, however--until the key exchange finishes, no new packets will be processed.

[show source] 
# File lib/net/ssh/transport/algorithms.rb, line 136
def rekey!
  @client_packet = @server_packet = nil
  @initialized = false
  send_kexinit
end