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

ALGORITHMS =

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

{
  host_key: %w[ssh-rsa ssh-dss
               [email protected]
               [email protected]],
  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 [email protected]
                 idea-cbc arcfour128 arcfour256 arcfour
                 aes128-ctr aes192-ctr aes256-ctr
                 cast128-ctr blowfish-ctr 3des-ctr none],
    
  hmac: %w[hmac-sha1 hmac-md5 hmac-sha1-96 hmac-md5-96
           hmac-ripemd160 [email protected]
           hmac-sha2-256 hmac-sha2-512 hmac-sha2-256-96
           hmac-sha2-512-96 none],
    
  compression: %w[none [email protected] zlib],
  language: %w[]
}

Constants included from Constants

Constants::DEBUG, Constants::DISCONNECT, Constants::IGNORE, 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 113

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

#algorithms ⇒ Object (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 99

def algorithms
  @algorithms
end

#compression_client ⇒ Object (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 86

def compression_client
  @compression_client
end

#compression_server ⇒ Object (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 89

def compression_server
  @compression_server
end

#encryption_client ⇒ Object (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 74

def encryption_client
  @encryption_client
end

#encryption_server ⇒ Object (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 77

def encryption_server
  @encryption_server
end

#hmac_client ⇒ Object (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 80

def hmac_client
  @hmac_client
end

#hmac_server ⇒ Object (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 83

def hmac_server
  @hmac_server
end

#host_key ⇒ Object (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 70

def host_key
  @host_key
end

#kex ⇒ Object (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 67

def kex
  @kex
end

#language_client ⇒ Object (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 92

def language_client
  @language_client
end

#language_server ⇒ Object (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 95

def language_server
  @language_server
end

#options ⇒ Object (readonly)

The hash of options used to initialize this object



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# File 'lib/net/ssh/transport/algorithms.rb', line 64

def options
  @options
end

#session ⇒ Object (readonly)

The underlying transport layer session that supports this object



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# File 'lib/net/ssh/transport/algorithms.rb', line 61

def session
  @session
end

#session_id ⇒ Object (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 102

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 105

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 156

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 143

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 172

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

#host_key_format ⇒ Object 



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# File 'lib/net/ssh/transport/algorithms.rb', line 181

def host_key_format
  case host_key
  when "[email protected]", "[email protected]"
    "ssh-rsa"
  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 177

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 165

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 133

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

#start ⇒ Object

Start the algorithm negotation

Raises:

  • (ArgumentError) 


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# File 'lib/net/ssh/transport/algorithms.rb', line 124

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