#+title: Password Security in Emacs Terminal Emulators
#+author: Robert McIntyre
#+email: rlm@mit.edu
#+description: emacs terminal password security
#+keywords: emacs, password, security, term
#+SETUPFILE: ../../aurellem/org/setup.org
#+INCLUDE: ../../aurellem/org/level-0.org
#+babel: :mkdirp yes :noweb yes :exports both

I use emacs for everything -- email, programming, document
preparation, planning... You name it, I do it! One thing which I use
emacs for is terminal emulation, which is where you create a buffer in
emacs where you can enter commands as if the buffer were a
terminal. Good terminal emulation packages for emacs include
=multi-term= and =term=.

* Watch Out for =view-lossage=!
However, if you are going to use terminal emulation in emacs, you have
to be careful around "sudo" prompts, and when logging into other
servers using ssh, because /the last 300 keystrokes you have typed in
emacs are available/ using =C-h l=, a help function in emacs which
displays the last keypresses you have typed.

#+begin_example
C-h l runs the command view-lossage, which is an interactive compiled
Lisp function in `help.el'.

It is bound to C-h l, <help> l.

(view-lossage)

Display last 300 input keystrokes.
#+end_example

Let's say my password is "sup3r-seekrit#7".

I open an emacs terminal using =M-x multi-term=, then do the following

#+begin_example
[~] $ ssh rlm@linerva.mit.edu
Password: 

Welcome to Linerva, the SIPB Linux dialup for MIT.
Linerva runs Debathena on Debian squeeze.
 http://linerva.mit.edu                           for more information
 blanche linerva-announce -a $USER          # for outage announcements
 linerva@mit.edu              (not IS&T) for questions and bug reports

Last login: Mon Mar  4 12:53:23 2013 from ella.csail.mit.edu
rlm@dr-wily:~$ exit
logout
Connection to linerva.mit.edu closed.
#+end_example

Now, when I type =C-h l=, I can see this:

#+begin_example
s s h SPC r l m @ l i n e r v a . m i t . e d u <return>
s u p 3 r - s e e k r i t # 7 <return> e x i t C-h l
#+end_example

Needless to say, this can be a security vulnerability.

* Solutions to this problem

 - If you don't ever type your password into an emacs terminal buffer,
   then you are not at risk. This can be accomplished by using ssh
   keyfiles or Kerberos for connecting to remote servers, and by
   enabling passwordless sudo.

 - You can disable emacs keylogging, though you then won't be able to
   use the =view-lossage= command anymore.

 - If there's no way for an attacker to get into your emacs process,
   then your passwords are safe. Still, you run the risk of someone
   physically near your computer using this method to view your
   password, as well as inadvertently exposing your password when
   showing someone what =view-lossage= does!

* Source Listing
#+html: <ul> <li> <a href="../org/emacs-password.org">This org file</a> </li> </ul>