Class: Net::SSH::Transport::Algorithms

Inherits:
Object
  • Object
show all
Includes:
Loggable, Constants
Defined in:
lib/net/ssh/transport/algorithms.rb

Overview

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.

Constant Summary collapse

DEFAULT_ALGORITHMS =

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

{
  host_key: %w[[email protected]
               [email protected]
               [email protected]
               ecdsa-sha2-nistp521
               ecdsa-sha2-nistp384
               ecdsa-sha2-nistp256
               [email protected]
               [email protected]
               ssh-rsa
               rsa-sha2-256
               rsa-sha2-512],

  kex: %w[ecdh-sha2-nistp521
          ecdh-sha2-nistp384
          ecdh-sha2-nistp256
          diffie-hellman-group-exchange-sha256
          diffie-hellman-group14-sha256
          diffie-hellman-group14-sha1],

  encryption: %w[aes256-ctr aes192-ctr aes128-ctr],

  hmac: %w[[email protected] [email protected]
           hmac-sha2-512 hmac-sha2-256
           hmac-sha1]
}.freeze
ALGORITHMS =

Define all algorithms, with the deprecated, supported by Net::SSH.

{
  host_key: DEFAULT_ALGORITHMS[:host_key] + %w[ssh-dss],

  kex: DEFAULT_ALGORITHMS[:kex] +
       %w[diffie-hellman-group-exchange-sha1
          diffie-hellman-group1-sha1],

  encryption: DEFAULT_ALGORITHMS[:encryption] +
              %w[aes256-cbc aes192-cbc aes128-cbc
                 [email protected]
                 blowfish-ctr blowfish-cbc
                 cast128-ctr cast128-cbc
                 3des-ctr 3des-cbc
                 idea-cbc
                 none],

  hmac: DEFAULT_ALGORITHMS[:hmac] +
        %w[hmac-sha2-512-96 hmac-sha2-256-96
           hmac-sha1-96
           hmac-ripemd160 [email protected]
           hmac-md5 hmac-md5-96
           none],

  compression: %w[none [email protected] zlib],
  language: %w[]
}.freeze

Constants included from Constants

Constants::DEBUG, Constants::DISCONNECT, Constants::IGNORE, Constants::KEXDH_GEX_GROUP, Constants::KEXDH_GEX_INIT, Constants::KEXDH_GEX_REPLY, Constants::KEXDH_GEX_REQUEST, Constants::KEXDH_INIT, Constants::KEXDH_REPLY, Constants::KEXECDH_INIT, Constants::KEXECDH_REPLY, Constants::KEXINIT, Constants::NEWKEYS, Constants::SERVICE_ACCEPT, Constants::SERVICE_REQUEST, Constants::UNIMPLEMENTED

Instance Attribute Summary collapse

Attributes included from Loggable

#logger

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Loggable

#debug, #error, #fatal, #info, #lwarn

Constructor Details

#initialize(session, options = {}) ⇒ Algorithms

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


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# File 'lib/net/ssh/transport/algorithms.rb', line 149

def initialize(session, options = {})
  @session = session
  @logger = session.logger
  @options = options
  @algorithms = {}
  @pending = @initialized = false
  @client_packet = @server_packet = nil
  prepare_preferred_algorithms!
end

Instance Attribute Details

#algorithmsObject (readonly)

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


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# File 'lib/net/ssh/transport/algorithms.rb', line 135

def algorithms
  @algorithms
end

#compression_clientObject (readonly)

The type of compression to use to compress packets being sent by the client.


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# File 'lib/net/ssh/transport/algorithms.rb', line 122

def compression_client
  @compression_client
end

#compression_serverObject (readonly)

The type of compression to use to decompress packets arriving from the server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 125

def compression_server
  @compression_server
end

#encryption_clientObject (readonly)

The type of the cipher to use to encrypt packets sent from the client to the server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 110

def encryption_client
  @encryption_client
end

#encryption_serverObject (readonly)

The type of the cipher to use to decrypt packets arriving from the server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 113

def encryption_server
  @encryption_server
end

#hmac_clientObject (readonly)

The type of HMAC to use to sign packets sent by the client.


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# File 'lib/net/ssh/transport/algorithms.rb', line 116

def hmac_client
  @hmac_client
end

#hmac_serverObject (readonly)

The type of HMAC to use to validate packets arriving from the server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 119

def hmac_server
  @hmac_server
end

#host_keyObject (readonly)

The type of host key that will be used for this session.


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# File 'lib/net/ssh/transport/algorithms.rb', line 106

def host_key
  @host_key
end

#kexObject (readonly)

The kex algorithm to use settled on between the client and server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 103

def kex
  @kex
end

#language_clientObject (readonly)

The language that will be used in messages sent by the client.


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# File 'lib/net/ssh/transport/algorithms.rb', line 128

def language_client
  @language_client
end

#language_serverObject (readonly)

The language that will be used in messages sent from the server.


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# File 'lib/net/ssh/transport/algorithms.rb', line 131

def language_server
  @language_server
end

#optionsObject (readonly)

The hash of options used to initialize this object


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# File 'lib/net/ssh/transport/algorithms.rb', line 100

def options
  @options
end

#sessionObject (readonly)

The underlying transport layer session that supports this object


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# File 'lib/net/ssh/transport/algorithms.rb', line 97

def session
  @session
end

#session_idObject (readonly)

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


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# File 'lib/net/ssh/transport/algorithms.rb', line 138

def session_id
  @session_id
end

Class Method Details

.allowed_packet?(packet) ⇒ Boolean

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

Returns:

  • (Boolean)

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# File 'lib/net/ssh/transport/algorithms.rb', line 141

def self.allowed_packet?(packet)
  (1..4).include?(packet.type) ||
  (6..19).include?(packet.type) ||
  (21..49).include?(packet.type)
end

Instance Method Details

#[](key) ⇒ Object

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


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# File 'lib/net/ssh/transport/algorithms.rb', line 193

def [](key)
  algorithms[key]
end

#accept_kexinit(packet) ⇒ Object

Called by the transport layer when a KEXINIT packet is received, 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.


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# File 'lib/net/ssh/transport/algorithms.rb', line 180

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) ⇒ Boolean

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.

Returns:

  • (Boolean)

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# File 'lib/net/ssh/transport/algorithms.rb', line 209

def allow?(packet)
  !pending? || Algorithms.allowed_packet?(packet)
end

#host_key_formatObject


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# File 'lib/net/ssh/transport/algorithms.rb', line 218

def host_key_format
  case host_key
  when /^([a-z0-9-]+)-cert-v\d{2}@openssh.com$/
    Regexp.last_match[1]
  else
    host_key
  end
end

#initialized?Boolean

Returns true if the algorithms have been negotiated at all.

Returns:

  • (Boolean)

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# File 'lib/net/ssh/transport/algorithms.rb', line 214

def initialized?
  @initialized
end

#pending?Boolean

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.

Returns:

  • (Boolean)

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# File 'lib/net/ssh/transport/algorithms.rb', line 202

def pending?
  @pending
end

#rekey!Object

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.


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# File 'lib/net/ssh/transport/algorithms.rb', line 170

def rekey!
  @client_packet = @server_packet = nil
  @initialized = false
  send_kexinit
end

#startObject

Start the algorithm negotation

Raises:

  • (ArgumentError)

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# File 'lib/net/ssh/transport/algorithms.rb', line 160

def start
  raise ArgumentError, "Cannot call start if it's negotiation started or done" if @pending || @initialized

  send_kexinit
end