How Can I Securely Obtain Password Input in C Without Echoing to the Console?

Secure Password Input in C

To protect user privacy, it's often desirable to prevent passwords entered via standard input from being echoed to the console. Here's how to disable echo using a system-agnostic approach:

Overview

This issue can be addressed on both Windows and UNIX-like operating systems. The solution involves modifying the standard input settings to disable echo.

Windows

For Windows systems, use the Win32 API:

#include <windows.h>

void SetStdinEcho(bool enable = true)
{
    HANDLE hStdin = GetStdHandle(STD_INPUT_HANDLE);
    DWORD mode;
    GetConsoleMode(hStdin, &mode);

    if (!enable)
        mode &= ~ENABLE_ECHO_INPUT;
    else
        mode |= ENABLE_ECHO_INPUT;

    SetConsoleMode(hStdin, mode);
}

UNIX-like Systems

For UNIX-like systems, use the termios library:

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

void SetStdinEcho(bool enable = true)
{
    struct termios tty;
    tcgetattr(STDIN_FILENO, &tty);
    if (!enable)
        tty.c_lflag &= ~ECHO;
    else
        tty.c_lflag |= ECHO;

    (void)tcsetattr(STDIN_FILENO, TCSANOW, &tty);
}

Usage

To suppress echoing while retrieving the password:

SetStdinEcho(false);
std::string password;
std::cin >> password;
SetStdinEcho(true);

Example

#include <iostream>
#include <string>

int main()
{
    SetStdinEcho(false);

    std::string password;
    std::cin >> password;

    SetStdinEcho(true);

    std::cout << password << std::endl;

    return 0;
}

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