Enter Password in C

Question

I am aware that it is not possible to echo the * while you type in standard ANSI C. But is there a way to display nothing while someone is typing their password in the console. What I mean is like the sudo prompts in a Unix/Linux terminal. Like if you type in the command: sudo cp /etc/somefile ~/somedir. You are usually prompted for the root password. And while you type it in, the terminal displays nothing. Is this effect possible in C? If it is, how?

Overhand

What's not possible about showing ""? printf(""); will do it. – Needlework

@Peter K.: I believe he's referring to the fact that all the standard input functions echo to the console. Sure, you can print *, but the character the user typed is already there. – Unmake

possible duplicate #1196918 – Christelchristen

tinyfiledialogs is a single C file (cross-platform) offering graphic and console basic dialogs (including an inputbox and a password box) sf.net/p/tinyfiledialogs – Obregon

Answer 1

The function that you are looking for is: getpass(). You will note, though, that it is marked as "LEGACY". Although it isn't going to go anywhere, the function doesn't allow the size of the input buffer to be specified, which makes it not a very good interface. As Jefromi has noted, the glibc manual provides portable example code for implementing getpass from scratch in a way that allows an arbitrary input size (and isn't LEGACY).

Segal

They should provide a getnpass() so not every programmer need to reinvent the wheel... – Anacreontic

Answer 2

sudo is written in C, so yes :). The getpass() function Safyan mentioned is probably what you want, but here's where the actual sudo tool does it if you're interested:

http://sudo.ws/repos/sudo/file/dc3bf870f91b/src/tgetpass.c#l70

Stupa

Answer 3

The poor-man's method of doing this is to read user input character by character, and after each character is received print out a backspace character followed by *. The output is technically sent to the console, but it is immediately erased and overwritten by an asterisk (often before that frame is even drawn to the screen). Note that this is not really a secure method and has several security holes, but for low-tech low-security applications, it works.

Rhaetia

Answer 4

*This is not ANSI C (Thanks Billy) sample

You can detect keypress with _kbhit(), then get the value using _getch(). Both function will not echo the content on screen.

#include <conio.h>          //For keyboard events
#include <stdio.h>          //Include this or iostream
#include <locale>           
int main()
{
    bool bContinue = true;
    char szBuffer[255] = {0};
    unsigned int nbufIndex = 0;
    while (bContinue)
    {
        if (_kbhit())
        {
            szBuffer[nbufIndex] = _getch();
            if (szBuffer[nbufIndex] == 0xD)
            {
                bContinue = false;
            }
            else
            {
                ++nbufIndex;
                printf("*");
            }
        }
    }
    printf("\n%s\n", szBuffer);
    return 0;
}

Falla

Note that this is not ANSI C. – Unmake

I don't think conio.h is likely to be available if you're compiling on UNIX or Linux. – Taut

Answer 5

#include <stdio.h>
#include <conio.h>

void main()
{

    char pwd[15];
    int i;
    printf("Enter Password : ");
    for(i=0;i<15;i++)
    {
    pwd[i]=getch();
        if(pwd[i]!='\r')
        {
            printf("*");
        }
        if(pwd[i]==13)
            break;
    }

    printf("\n     \nPassword is : ");
    for(i=0;i<15;i++)
    {
        printf("%d ",pwd[i]);
    }
}

Deckert

conio.h does not exist in the Linux environment, see #8792817. Further can you explain a little more about your solution? – Addax

Welcome to Stackoverflow. Please explain your answer so others can understand easier. – Ka

For those who are code in windows TurboC/C++, visual Studio editor ------------>Yes, As someone want to start a minor project or any of the beginner wants to get asterisk at the place of array of character or string in C / C++ programming language. . As well as the electrical engineering student may also use this code for the asterisk at the place of input on the display and further proceed. – Deckert

Answer 6

I recently wrote this! To read each character individually and to stop printing them you need to disable echoing and canonical mode (which stops input from being read until the return key is pressed).

To achieve this you need to change the terminal attributes:

#include <termios.h>
#include <unistd.h>
#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>

void rawChange(int opt) {
    struct termios new;

    if (tcgetattr (STDIN_FILENO, &new) != 0)
        exit(1);    // if something goes wrong exit program

    if (opt == 1)
        new.c_lflag &= ~(ECHO | ICANON);    // to enable
    else
        new.c_lflag |= (ECHO | ICANON);    // to reset

    if (tcsetattr (STDIN_FILENO, TCSAFLUSH, &new) != 0)
        exit(1);    // if something goes wrong exit program
}

Now you just get the password character by character, printing '*' each time a character is read:

#define RETURN_KEY 10
#define DELETE_KEY 127
#define CURSOR_LEFT "\x1b[D"    // cursor moves one unit to the left
#define MAX_PASSWORD_LENGTH 64


char * getPassword(void) {

    static char password[MAX_PASSWORD_LENGTH + 1];
    char c; int i = 0, finish = 0;

    rawChange(0);   // disable echo and canonical mode
    printf("enter password: ");
        
    while (!finish) {
        finish = (c = getchar()) == RETURN_KEY;

        if (c == DELETE_KEY) { // allows to use delete key
            if (i > 0) {
                i--;
                printf("%s %s", CURSOR_LEFT, CURSOR_LEFT);
            }
            continue;
        }
        
        if (!finish && i == MAX_PASSWORD_LENGTH)
            continue;

        password[i++] = finish ? '\0' : c;
        printf(finish ? "" : "*");
    }

    rawChange(1);   // reenable echo and canonical mode
    return password;
}

I learned to do this in this course which teaches how to make a text editor from scratch. If you want a better explanation of everything definitely check it out!

(Edit: just noticed how old this post is but oh well)

Hysteric