[Caml-list] How to read a password without displaying it?

[Caml-list] How to read a password without displaying it?

[David MENTRE]

Hello,

In my textual OCaml program, I would like to read a password. Currently,
I'm using read_line which is not very satisfying as the password is
display on screen.

  let passwd = read_line () in

Any idea how I might read the password without displaying it? 

I tried the following function, using input_char, but the password is
still displayed on screen:

let read_password () =
  let password_chars = ref [] in
  let loop = ref true in
  while !loop do
    let c = input_char stdin in
    if c <> '\n' then (
      password_chars := c :: !password_chars
     ) else (
      loop := false
     )
  done;
  let password = String.create (List.length !password_chars) in
  let _, res = List.fold_right (fun c (i, s) -> s.[i] <- c; (i+1, s))
      !password_chars (0, password) in
  res


Many thanks in advance for any help,
Yours,
d.
-- 
 David Mentré <dmentre@linux-france.org>

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Re: [Caml-list] How to read a password without displaying it?

[Basile STARYNKEVITCH]

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On Sat, Feb 07, 2004 at 01:53:20PM +0100, David MENTRÉ wrote:
> 
> In my textual OCaml program, I would like to read a password. Currently,
> I'm using read_line which is not very satisfying as the password is
> display on screen.
> 
>   let passwd = read_line () in
> 
> Any idea how I might read the password without displaying it? 

I have a few ideas, but I'm sure you already know them. First, I
assume you have (and target only) a Unix-like system. All tricks below
are probably non portable to Windows (an OS I never coded for, which I
don't know).

The first trick would be to call the C function getpass (which,
according to its man page, is obsolete).

You could also use the [in]famous GNU readline C library.

You could also use the ncurses library.

If you have an X11 server (but you apparently want a textual only
interface), you might use (shameless plug) my GUIS gtk "server"
program from http://starynkevitch.net/Basile/guisdoc.html You'll just
have to code a few lines of Python or Ruby code creating a simple GUI
interface. The ocaml application communicates with it using textual
protocols. Of course, you could also run some tiny command which ask
for your password.

You might also issue the ioctl (that you need to code in C and call
from Ocaml) which supress the echo and make the keyboard working in
raw (non cooked) mode. I forgot the ugly details. You have to reset
your tty to its previous state before exiting (or just after having
got the password)

> 
> I tried the following function, using input_char, but the password is
> still displayed on screen:
> 
> let read_password () =
>   let password_chars = ref [] in
>   let loop = ref true in
>   while !loop do
>     let c = input_char stdin in
>     if c <> '\n' then (
>       password_chars := c :: !password_chars
>      ) else (
>       loop := false
>      )
>   done;
>   let password = String.create (List.length !password_chars) in
>   let _, res = List.fold_right (fun c (i, s) -> s.[i] <- c; (i+1, s))
>       !password_chars (0, password) in
>   res

I belive this should work if it where boxed by appriate ioctl removing
the echo.

I believe that you cannot do anything without a little C code (because
ioctl or fcntl are not available to Ocaml, mostly because typing it is
a nightmare)

Regards.

-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile<at>starynkevitch<dot>net 
aliases: basile<at>tunes<dot>org = bstarynk<at>nerim<dot>net
8, rue de la Faïencerie, 92340 Bourg La Reine, France

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Re: [Caml-list] How to read a password without displaying it?

[Maxence Guesdon]

Hello,

In Cash (http://pauillac.inria.fr/cash/), you can turn the echo
of the tty on and off. It may be what you need.

Hope this helps,

-- 
Maxence Guesdon

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Re: [Caml-list] How to read a password without displaying it?

[David MENTRE]

Thank you Basile and Maxence for your replies,

In fact, I wanted to do that in caml only, to be portable on Windows and
I'm relunctant to bind to C code. However, from what you said, it seems
impossible.

I tried following trick, using '\b' on output. Strangely enough, the
output_char have no effect, even if I do a flush. The '*' are printed
*after* I do a <RETURN> on my terminal.  I don't understand this
behavior. The flush should send the caracters to the terminal.

let read_password () =
  let password_chars = ref [] in
  let loop = ref true in
  while !loop do
    let c = input_char stdin in
    if c <> '\n' then (
      password_chars := c :: !password_chars;
      output_char stdout '\b';
      output_char stdout '*';
      flush_all ();
     ) else (
      loop := false
     )
  done;
  let password = String.create (List.length !password_chars) in
  let _, res = List.fold_right (fun c (i, s) -> s.[i] <- c; (i+1, s))
      !password_chars (0, password) in
  res


Yours,
d.
-- 
 David Mentré <dmentre@linux-france.org>

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Re: [Caml-list] How to read a password without displaying it?

[David MENTRE]

David MENTRE <dmentre@linux-france.org> writes:

> I tried following trick, using '\b' on output. Strangely enough, the
> output_char have no effect, even if I do a flush. The '*' are printed
> *after* I do a <RETURN> on my terminal.  I don't understand this
> behavior. The flush should send the caracters to the terminal.

Oops, I remembered my old unix programming. The shell (or whatever in
front of the caml program) sends the whole line after <CR>. So my output
is done on the following line. (sight)

Yours,
d.
-- 
 david.mentre@wanadoo.fr

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Re: [Caml-list] How to read a password without displaying it?

[Remi Vanicat]

David MENTRE <dmentre@linux-france.org> writes:

> Thank you Basile and Maxence for your replies,
>
> In fact, I wanted to do that in caml only, to be portable on Windows
> and I'm relunctant to bind to C code. However, from what you said,
> it seems impossible.

Well, I would try to use the Terminal interface of the Unix library :

open Unix

let read_pass () =
  let attr = tcgetattr stdin in
  tcsetattr stdin TCSAFLUSH { attr with c_echo = false };
  let line = read_line () in
  tcsetattr stdin TCSAFLUSH attr;
  line

It work. Of course you could do something to print * when the user
type something, but this is a first solution. By the way i don't know
if this work on windows.

-- 
Rémi Vanicat

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Re: [Caml-list] How to read a password without displaying it?

[Alain.Frisch]

On Sat, 7 Feb 2004, David MENTRE wrote:

> Any idea how I might read the password without displaying it?

The field c_echo in the record type Unix.terminal_io might be the
solution.

-- Alain

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Re: [Caml-list] How to read a password without displaying it?

[David MENTRE]

Hello Alain,

Alain.Frisch@ens.fr writes:

> The field c_echo in the record type Unix.terminal_io might be the
> solution.

Thanks a lot Alain, you found the right solution.

Here is the working code:

open Unix
[...]
let read_password () =
  let term_init = tcgetattr stdin in
  let term_no_echo = { term_init with c_echo = false; } in
  tcsetattr stdin TCSANOW term_no_echo;
  let password = read_line () in
  tcsetattr stdin TCSAFLUSH term_init;
  password


Many thanks,
d.
-- 
 David Mentré <dmentre@linux-france.org>

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Re: [Caml-list] How to read a password without displaying it?

[David Brown]

On Sat, Feb 07, 2004 at 04:12:01PM +0100, David MENTRE wrote:

> open Unix
> [...]
> let read_password () =
>   let term_init = tcgetattr stdin in
>   let term_no_echo = { term_init with c_echo = false; } in
>   tcsetattr stdin TCSANOW term_no_echo;
>   let password = read_line () in
>   tcsetattr stdin TCSAFLUSH term_init;
>   password

The only suggestion would be to put the read_line in a try clause, and
restore the terminal settings if an exception is raised.  Otherwise,
pressing ^C leaves the terminal with echo off.

Dave

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