class Net::SSH::Transport::CipherFactory

Implements a factory of OpenSSL cipher algorithms.

Constants

KEY_LEN_OVERRIDE

Ruby's OpenSSL bindings always return a key length of 16 for RC4 ciphers resulting in the error: OpenSSL::CipherError: key length too short. The following ciphers will override this key length.

SSH_TO_OSSL

Maps the SSH name of a cipher to it's corresponding OpenSSL name

Public Class Methods

get(name, options={}) click to toggle source

Retrieves a new instance of the named algorithm. The new instance will be initialized using an iv and key generated from the given iv, key, shared, hash and digester values. Additionally, the cipher will be put into encryption or decryption mode, based on the value of the encrypt parameter.

# File lib/net/ssh/transport/cipher_factory.rb, line 57
def self.get(name, options={})
  ossl_name = SSH_TO_OSSL[name] or raise NotImplementedError, "unimplemented cipher `#{name}'"
  return IdentityCipher if ossl_name == "none"
  cipher = OpenSSL::Cipher.new(ossl_name)

  cipher.send(options[:encrypt] ? :encrypt : :decrypt)

  cipher.padding = 0

  cipher.extend(Net::SSH::Transport::CTR) if (name =~ /-ctr(@openssh.org)?$/)
  cipher.iv = Net::SSH::Transport::KeyExpander.expand_key(cipher.iv_len, options[:iv], options) if ossl_name != "rc4"

  key_len = KEY_LEN_OVERRIDE[name] || cipher.key_len
  cipher.key_len = key_len
  cipher.key = Net::SSH::Transport::KeyExpander.expand_key(key_len, options[:key], options)
  cipher.update(" " * 1536) if (ossl_name == "rc4" && name != "arcfour")

  return cipher
end
get_lengths(name, options = {}) click to toggle source

Returns a two-element array containing the [ key-length, block-size ] for the named cipher algorithm. If the cipher algorithm is unknown, or is “none”, 0 is returned for both elements of the tuple. if :iv_len option is supplied the third return value will be ivlen

# File lib/net/ssh/transport/cipher_factory.rb, line 82
def self.get_lengths(name, options = {})
  ossl_name = SSH_TO_OSSL[name]
  if ossl_name.nil? || ossl_name == "none"
    result = [0, 0]
    result << 0 if options[:iv_len]
  else
    cipher = OpenSSL::Cipher.new(ossl_name)
    key_len = KEY_LEN_OVERRIDE[name] || cipher.key_len
    cipher.key_len = key_len

    result = [key_len, ossl_name=="rc4" ? 8 : cipher.block_size]
    result << cipher.iv_len if options[:iv_len]
  end
  result
end
supported?(name) click to toggle source

Returns true if the underlying OpenSSL library supports the given cipher, and false otherwise.

# File lib/net/ssh/transport/cipher_factory.rb, line 46
def self.supported?(name)
  ossl_name = SSH_TO_OSSL[name] or raise NotImplementedError, "unimplemented cipher `#{name}'"
  return true if ossl_name == "none"
  return OpenSSL::Cipher.ciphers.include?(ossl_name)
end