man readpassphrase (3): get a passphrase from the user

LIBRARY

Lb libbsd

SYNOPSIS

Fd #include <bsd/readpassphrase.h> Ft char * Fn readpassphrase const char *prompt char *buf size_t bufsiz int flags

DESCRIPTION

The Fn 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, 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.

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.

Fn readpassphrase takes the following optional Fa flags :

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               force read of passphrase from stdin

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, 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.

FILES

/dev/tty

EXAMPLES

The following code fragment will read a passphrase from /dev/tty into the buffer Fa 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");
...
memset(passbuf, 0, sizeof(passbuf));

ERRORS

Bq Er EINTR: The Fn readpassphrase function was interrupted by a signal.
Bq Er EINVAL: The bufsiz argument was zero.
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 SIGTTIN signal, or the process group is orphaned.
Bq Er EMFILE: The process has already reached its limit for open file descriptors.
Bq Er ENFILE: The system file table is full.
Bq Er ENOTTY: There is no controlling terminal and the RPP_REQUIRE_TTY flag was specified.

SIGNALS

Fn 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 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 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, Fn readpassphrase will reprint the prompt and the user may then enter a passphrase.

STANDARDS

The Fn readpassphrase function is an Ox extension and should not be used if portability is desired.

HISTORY

The Fn readpassphrase function first appeared in Ox 2.9 .