READPASSPHRASE (3) | C library functions | Unix Manual Pages | :man▋
readpassphrase - get a passphrase from the user
.In readpassphrase.h "char *" readpassphrase "const char *prompt" "char *buf" "size_t bufsiz" "int flags"
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 readpassphrase function takes the following optional 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 |
The calling process should zero the passphrase as soon as possible to avoid leaving the cleartext passphrase visible in the processs address space.
Upon successful completion, readpassphrase returns a pointer to the null-terminated passphrase. If an error is encountered, the terminal state is restored and a NULL pointer is returned.
The following code fragment will read a passphrase from /dev/tty into the buffer passbuf.
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 will catch the following signals:
| SIGINT |
| || |
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 signal 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.
| || The readpassphrase function was interrupted by a signal. |
| || 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. |
| || 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. |
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