.\"	$OpenBSD: readpassphrase.3,v 1.20 2014/03/06 23:03:18 millert Exp $
.\"
.\" Copyright (c) 2000, 2002 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
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.\" Agency (DARPA) and Air Force Research Laboratory, Air Force
.\" Materiel Command, USAF, under agreement number F39502-99-1-0512.
.\"
.Dd $Mdocdate: March 6 2014 $
.Dt READPASSPHRASE 3
.Os
.Sh NAME
.Nm readpassphrase
.Nd get a passphrase from the user
.Sh SYNOPSIS
.In readpassphrase.h
.Ft char *
.Fn readpassphrase "const char *prompt" "char *buf" "size_t bufsiz" "int flags"
.Sh DESCRIPTION
The
.Fn readpassphrase
function displays a prompt to, and reads in a passphrase from,
.Pa /dev/tty .
If this file is inaccessible
and the
.Dv RPP_REQUIRE_TTY
flag is not set,
.Fn readpassphrase
displays the prompt on the standard error output and reads from the standard
input.
In this case it is generally not possible to turn off echo.
.Pp
Up to
.Fa bufsiz
- 1 characters (one is for the NUL) are read into the provided buffer
.Fa buf .
Any additional
characters and the terminating newline (or return) character are discarded.
.Pp
The
.Fa flags
argument is the bitwise
.Tn OR
of zero or more of the following values:
.Bd -literal -offset indent
RPP_ECHO_OFF		turn off echo (default behavior)
RPP_ECHO_ON		leave echo on
RPP_REQUIRE_TTY		fail if there is no tty
RPP_FORCELOWER		force input to lower case
RPP_FORCEUPPER		force input to upper case
RPP_SEVENBIT		strip the high bit from input
RPP_STDIN		read passphrase from stdin; ignore prompt
.Ed
.Pp
The calling process should zero the passphrase as soon as possible to
avoid leaving the cleartext passphrase visible in the process's address
space.
.Sh RETURN VALUES
Upon successful completion,
.Fn readpassphrase
returns a pointer to the NUL-terminated passphrase.
If an error is encountered, the terminal state is restored and
a null pointer is returned.
.Sh FILES
.Bl -tag -width /dev/tty -compact
.It Pa /dev/tty
.El
.Sh EXAMPLES
The following code fragment will read a passphrase from
.Pa /dev/tty
into the buffer
.Fa passbuf .
.Bd -literal -offset indent
char passbuf[1024];

\&...

if (readpassphrase("Response: ", passbuf, sizeof(passbuf),
    RPP_REQUIRE_TTY) == NULL)
	errx(1, "unable to read passphrase");

if (compare(transform(passbuf), epass) != 0)
	errx(1, "bad passphrase");

\&...

explicit_bzero(passbuf, sizeof(passbuf));
.Ed
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINTR
The
.Fn readpassphrase
function was interrupted by a signal.
.It Bq Er EINVAL
The
.Ar bufsiz
argument was zero.
.It Bq Er EIO
The process is a member of a background process attempting to read
from its controlling terminal, the process is ignoring or blocking
the
.Dv SIGTTIN
signal, or the process group is orphaned.
.It Bq Er EMFILE
The process has already reached its limit for open file descriptors.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er ENOTTY
There is no controlling terminal and the
.Dv RPP_REQUIRE_TTY
flag was specified.
.El
.Sh SIGNALS
.Fn readpassphrase
will catch the following signals:
.Bd -literal -offset indent
SIGALRM		SIGHUP		SIGINT
SIGPIPE		SIGQUIT		SIGTERM
SIGTSTP		SIGTTIN		SIGTTOU
.Ed
.Pp
When one of the above signals is intercepted, terminal echo will
be restored if it had previously been turned off.
If a signal handler was installed for the signal when
.Fn readpassphrase
was called, that handler is then executed.
If no handler was previously installed for the signal then the
default action is taken as per
.Xr sigaction 2 .
.Pp
The
.Dv SIGTSTP ,
.Dv SIGTTIN ,
and
.Dv SIGTTOU
signals (stop signals generated from keyboard or due to terminal I/O
from a background process) are treated specially.
When the process is resumed after it has been stopped,
.Fn readpassphrase
will reprint the prompt and the user may then enter a passphrase.
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr getpass 3
.Sh STANDARDS
The
.Fn readpassphrase
function is an
.Ox
extension and should not be used if portability is desired.
.Sh HISTORY
The
.Fn readpassphrase
function first appeared in
.Ox 2.9 .