NAME

     readpassphrase — get a passphrase from the user

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <readpassphrase.h>
     (See libbsd(7) for include usage.)

     char *
     readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags);

DESCRIPTION

     The readpassphrase() function displays a prompt to, and reads in a passphrase from,
     /dev/tty.  If this file is inaccessible and the RPP_REQUIRE_TTY flag is not set,
     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.

     Up to bufsiz - 1 characters (one is for the NUL) are read into the provided buffer buf.  Any
     additional characters and the terminating newline (or return) character are discarded.

     The flags argument is the bitwise OR of zero or more of the following values:

           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

     The calling process should zero the passphrase as soon as possible to avoid leaving the
     cleartext passphrase visible in the process's address space.

RETURN VALUES

     Upon successful completion, 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.

FILES

     /dev/tty

EXAMPLES

     The following code fragment will read a passphrase from /dev/tty into the buffer passbuf.

           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));

ERRORS

     [EINTR]            The readpassphrase() function was interrupted by a signal.

     [EINVAL]           The bufsiz argument was zero.

     [EIO]              The process is a member of a background process attempting to read from
                        its controlling terminal, the process is ignoring or blocking the SIGTTIN
                        signal, or the process group is orphaned.

     [EMFILE]           The process has already reached its limit for open file descriptors.

     [ENFILE]           The system file table is full.

     [ENOTTY]           There is no controlling terminal and the RPP_REQUIRE_TTY flag was
                        specified.

SIGNALS

     readpassphrase() will catch the following signals:

           SIGALRM         SIGHUP          SIGINT
           SIGPIPE         SIGQUIT         SIGTERM
           SIGTSTP         SIGTTIN         SIGTTOU

     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
     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 sigaction(2).

     The SIGTSTP, SIGTTIN, and 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, readpassphrase() will reprint the prompt and the user may then
     enter a passphrase.

SEE ALSO

     sigaction(2), getpass(3)

STANDARDS

     The readpassphrase() function is an BSD extension and should not be used if portability is
     desired.

HISTORY

     The readpassphrase() function first appeared in OpenBSD 2.9 and FreeBSD 4.6.