Two Factor SSH Authentication

two_factor_ssh.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'rotp'
require 'time'

user = ARGV[0]
secret = ARGV[1]
abort unless user and secret

trap("INT") do
  abort
end

class TwoFactorSSH
  LOG_FILE = "#{ENV['HOME']}/.ssh/two_factor.log"

  def initialize(options={})
    @user = options[:user]
    @secret = options[:secret]
    @debug = options[:debug]

    @client_ip = ENV['SSH_CLIENT'].split.first

    last_log_entry = File.read(LOG_FILE).each_line.grep(/^#{@user}@#{@client_ip}/).last rescue nil
    if last_log_entry
      @last_login = Time.parse(last_log_entry.split("\t")[1])
      @last_auth = Time.parse(last_log_entry.split("\t")[2])
      @remember_me = last_log_entry.split("\t")[3].strip
    end
  end

  def run!
    begin
      STDERR.write "Connection from #{@user}@#{@client_ip}\n" if @debug 
      unless already_validated?
        @validation_code = get_validation_code
        abort unless validates?
        @remember_me = get_remember_me
      end
      log_access
      shell_out!
    rescue Exception => e
      STDERR.write "Logout\n\n"
      puts e.message if @debug
      puts e.backtrace.join("\n") if @debug
    end
  end

  def already_validated?
    return false unless @last_auth and @remember_me
    case @remember_me
      when 'a' then return true
      when 'd' then return true if @last_auth > Time.now.utc - (60*60*24) 
      when 'm' then return true if @last_auth > Time.now.utc - (60*60*24*30)
      when 'y' then return true if @last_auth > Time.now.utc - (60*60*24*365)
      else return false
    end 
  end

  def get_validation_code 
    STDERR.write "#{ENV['USER']}@#{`hostname -s`.strip}:~$ "
    until validation_code = STDIN.gets.strip
      sleep 1
    end; validation_code
  end

  def validates?
    @validation_code == ROTP::TOTP.new(@secret).now.to_s
    @last_auth = Time.now.utc
  end

  def get_remember_me
    STDERR.write "Remember this auth? (Never, Always, Day, Month, Year): "
    until answer = STDIN.gets.strip
      sleep 1
    end; answer
  end

  def log_access
    log = "#{@user}@#{@client_ip}\t#{Time.now.utc.to_s}\t#{@last_auth}\t#{@remember_me}"
    `echo "#{log}" >> #{LOG_FILE}`
  end

  def shell_out!
    if ENV['SSH_ORIGINAL_COMMAND']
      Kernel.exec ENV['SSH_ORIGINAL_COMMAND']
    elsif File.exists?('/usr/bin/motd+shell')
      Kernel.exec '/usr/bin/motd+shell'
    else
      Kernel.exec ENV['SHELL']
    end
  end

end

TwoFactorSSH.new(:user => user, :secret => secret, :debug => true).run!