Is there an alternative to getpass?

[unregistered]

for concealing password input since the man page indicates that it is obsolete

[chrisname]

I'm not sure of an alternative, but I have nothing to do, so here's one I wrote:

getpassword.h

#ifndef _GETPASSWORD_H
#define _GETPASSWORD_H

#ifdef __cplusplus
# include <cstdio>
# include <cstdlib>
#else
# include <stdio.h>
# include <stdlib.h>
#endif

#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(WINDOWS)\
    || defined(__WINDOWS__)
# ifndef WINDOWS
#  define WINDOWS
# endif
#elif defined(unix) || defined(UNIX) || defined(__UNIX__) || defined(POSIX)    \
      || defined(__POSIX__) || defined(CYGWIN)
# ifndef POSIX
#  define POSIX
# endif
#endif

#if defined(WINDOWS)
# include <windows.h>
#elif defined(POSIX)
# include <unistd.h>
# include <termios.h>
#endif

#ifdef __cplusplus
extern "C" {
#endif

/**
 * \brief Read a password without character echoing.
 * \note Input ends only when an EOF or LF character is encountered.
 * \param prompt Password prompt, if NULL "Password: " is used. If empty ("")
 * no prompt is used.
 * \param buffer Somewhere to store the password. This will be made larger if
 * necessary, although the enlargening operation will be slow. If NULL, the function fails.
 * \param replacement Character to print instead of printing input characters.
 * If this is '\0'; none is used.
 * \return 0 on success or -1 on error.
 */
int getpassword(const char* prompt, char** buffer, unsigned* sz, char replacement);

#ifdef __cplusplus
}
#endif

#endif /* ! _GETPASSWORD_H */ 

getpassword.c

#include "getpassword.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * \brief Read a password without character echoing.
 * \note Input ends only when an EOF or LF character is encountered.
 * \param prompt Password prompt, if NULL "Password: " is used. If empty ("")
 * no prompt is used.
 * \param buffer Somewhere to store the password. This will be made larger if
 * necessary, although the enlargening operation will be slow. If NULL, the function fails.
 * \param replacement Character to print instead of printing input characters.
 * If this is '\0'; none is used.
 * \return 0 on success or -1 on error.
 */
int getpassword(const char* prompt, char** buffer, unsigned* sz, char replacement)
{
	if (!buffer)
		return -1;

	/*
	 * Decide what prompt to print, if any, and then print it
	 */
	const char* default_prompt = "Password: ";
	if (prompt != NULL) {
		fprintf(stderr, "%s", prompt);
	} else if (prompt != "") {
		fprintf(stderr, "%s", default_prompt);
	}
	
	/*
	 * Disable character echoing and line buffering
	 */	
#if defined(WINDOWS)
	HANDLE hstdin = GetStdHandle(STD_INPUT_HANDLE);
	DWORD mode;
	
	if (!GetConsoleMode(hstdin, &mode))
		return -1;

	if (hstdin == INVALID_HANDLE_VALUE || !(SetConsoleMode(hstdin, 0))
		return -1; /* Failed to disable buffering */
#elif defined(POSIX)
	struct termios tty_attr;
	
	if (tcgetattr(STDIN_FILENO, &tty_attr) < 0)
		return -1;

	const tcflag_t c_lflag = tty_attr.c_lflag; /* Allows us to restore this later */
	tty_attr.c_lflag &= ~ICANON;
	tty_attr.c_lflag &= ~ECHO;

	if (tcsetattr(STDIN_FILENO, 0, &tty_attr) < 0)
		return -1;
#endif
	
	int i = 0,
	    c = 0;
	for (; (c = getchar()) != '\n' && c != EOF; ++i) {
		/*
		 * If the buffer gets too full, expand it
		 */
		if (i > *sz) {
			if (!realloc(*buffer, *sz))
				return -1;
			(*sz) += 1;
		}
			
		if (replacement)
			putchar(replacement);
		
		(*buffer)[i] = c;
	}
	
	if (replacement)
		putchar('\n');
	
	/* 
	 * Re-enable character echoing and line buffering
	 */
#if defined(WINDOWS)
	if (!SetConsoleMode(hstdin, mode))
		return -1;
#elif defined(POSIX)
	tty_attr.c_lflag = c_lflag;

	if (tcsetattr(STDIN_FILENO, 0, &tty_attr) < 0)
		return -1;
#endif
	return 0;
}

#ifdef __cplusplus
}
#endif 

main.c (just to show it working)

#include "getpassword.h"

#ifdef __cplusplus
# include <cstdio>
# include <cstdlib>
# include <cstring>
#else
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
#endif

#define BUFFERSIZE 4

int main()
{
	const char* validpassword = "OpenSesame";
	unsigned len = BUFFERSIZE;
	char* buffer = (char*)calloc(len, 1);
	
	getpassword("Password: ", &buffer, &len, '*');
	
	printf("%s.\n", (strcmp(validpassword, buffer) == 0) ? "Accepted" : "Rejected");
	
	free(buffer);
	return 0;
}

It works a little like the C getline() function in that the buffer you supply is expanded if necessary, although it might be slow to resize the buffer for every character that is too large. This means that it's safe from buffer overflow. It also has an advantage over getpass() in that you can specify a character to print instead of just turning character echoing off. It also works on Windows, but it isn't completely portable - it won't work on just any system that happens to have a working C library unless that library contains POSIX or Windows API extensions. The code works with a C or C++ compiler.

I haven't tested the Windows code but it should work.

I got the Windows API code from here: http://www.cplusplus.com/forum/beginner/3329/#msg13776