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READPASSPHRASE(3) Library Functions Manual READPASSPHRASE(3)

readpassphrase — get a passphrase from the user

#include <readpassphrase.h>

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

The () 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 () function takes the following optional flags:

turn off echo (default behavior)
leave echo on
fail if there is no tty
force input to lower case
force input to upper case
strip the high bit from input
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.

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.

/dev/tty
 

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");

...

memset(passbuf, 0, sizeof(passbuf));

[]
The readpassphrase() function was interrupted by a signal.
[]
The bufsiz argument was zero.
[]
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.
[]
The process has already reached its limit for open file descriptors.
[]
The system file table is full.
[]
There is no controlling terminal and the RPP_REQUIRE_TTY flag was specified.

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

sigaction(2), getpass(3)

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

The readpassphrase() function first appeared in OpenBSD 2.9.

May 31, 2007 FreeBSD-12.0