class Net::SSH::Transport::Session

def select_host_key_verifier(verify_host_key)

is raised.
to :verify, it is returned directly. Otherwise, an exception
strict Secure verifier is returned. If the argument happens to respond
:very, the Strict verifier is returned. If it is :secure, the even more
returned. If it is false, the Null verifier is returned, and if it is
the parameter. When true or nil, the default Lenient verifier is
Instantiates a new host-key verification class, based on the value of 
def select_host_key_verifier(verify_host_key)
  case verify_host_key
  when true, nil then
    Net::SSH::Verifiers::Lenient.new
  when false then
    Net::SSH::Verifiers::Null.new
  when :very then
    Net::SSH::Verifiers::Strict.new
  when :secure then
    Net::SSH::Verifiers::Secure.new
  else
    if verify_host_key.respond_to?(:verify)
      verify_host_key
    else
      raise(
        ArgumentError,
        "Invalid argument to :verify_host_key (or deprecated " \
        ":paranoid): #{verify_host_key.inspect}"
      )
    end
  end
end