Tutorial :Getting a password in C without using getpass (3)?



Question:

I could use getpass() to get a password. However, the man page says:

This function is obsolete. Do not use it.

What is the current way to get a password from the user's terminal without echoing it, in a POSIX-compliant way? [Originally I said "portably", but my intention was to avoid using an obsolete function.]


Solution:1

this should work on linux/macosx, a windows version should use Get/Set ConsoleMode

#include <stdio.h>  #include <stdlib.h>  #include <termios.h>    int  main(int argc, char **argv)  {      struct termios oflags, nflags;      char password[64];        /* disabling echo */      tcgetattr(fileno(stdin), &oflags);      nflags = oflags;      nflags.c_lflag &= ~ECHO;      nflags.c_lflag |= ECHONL;        if (tcsetattr(fileno(stdin), TCSANOW, &nflags) != 0) {          perror("tcsetattr");          return EXIT_FAILURE;      }        printf("password: ");      fgets(password, sizeof(password), stdin);      password[strlen(password) - 1] = 0;      printf("you typed '%s'\n", password);        /* restore terminal */      if (tcsetattr(fileno(stdin), TCSANOW, &oflags) != 0) {          perror("tcsetattr");          return EXIT_FAILURE;      }        return 0;  }  


Solution:2

You could use the ncurses library to read from standard input without echoing the results to the screen. (Call noecho() before getting any input). The library has been around for ages and works on a wide variety of platforms (the windows version can be found here)


Solution:3

Even though this is a very old question that has already been answered, here's what I've been using (which is very similar to the accepted answer):

#include <termios.h>  #include <cstdio>    //  // The following is a slightly modifed version taken from:  // http://www.gnu.org/software/libc/manual/html_node/getpass.html  //  ssize_t my_getpass (char *prompt, char **lineptr, size_t *n, FILE *stream)  {      struct termios _old, _new;      int nread;        /* Turn echoing off and fail if we can’t. */      if (tcgetattr (fileno (stream), &_old) != 0)          return -1;      _new = _old;      _new.c_lflag &= ~ECHO;      if (tcsetattr (fileno (stream), TCSAFLUSH, &_new) != 0)          return -1;        /* Display the prompt */      if (prompt)          printf("%s", prompt);        /* Read the password. */      nread = getline (lineptr, n, stream);        /* Remove the carriage return */      if (nread >= 1 && (*lineptr)[nread - 1] == '\n')      {          (*lineptr)[nread-1] = 0;          nread--;      }      printf("\n");        /* Restore terminal. */      (void) tcsetattr (fileno (stream), TCSAFLUSH, &_old);        return nread;  }    //  // Test harness - demonstrate calling my_getpass().  //  int main(int argc, char *argv[])  {      size_t maxlen = 255;      char pwd[maxlen];      char *pPwd = pwd; // <-- haven't figured out how to avoid this.        int count = my_getpass((char*)"Enter Password: ", &pPwd, &maxlen, stdin);        printf("Size of password: %d\nPassword in plaintext: %s\n", count, pwd);        return 0;  }  


Solution:4

According to the University of Milwaukee's documentation it is obsolete because:

The getpass() function is not threadsafe because it manipulates global signal state.

The getpass() function is scheduled to be withdrawn from a future version of the X/Open CAE Specification.


Solution:5

On windows, you can probably use the SetConsoleMode api, described here.


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