hide what's written to a file

[kristy]

I want to write something to a file, but I don't want what the user types to show up in the Terminal. How can this be done?

Thanks in advance.

[kristy]

Thank you for replying. I did a search for encryption, but didn't find anything after skimming through some of the results. Maybe it's me that's slow, but how can this come under the category encryption? I don't want anything encrypted - I just want zero output to the Terminal.

[Magos]

getch()

[kristy]

Thank you. I've read a bit in getch()'s man page, but it makes very little sense. I've also tried to use noecho(), but no matter what function I use from the <curses.h>, all I get is errors. The compiler keeps complaining about symbols that aren't found. What am I missing? Is there a tutorial out there (I didn't manage to locate any with google) on getch() or noecho()?

[Draco]

post your code so we can read it and help you

[Lynux-Penguin]

i think you need to do

gcc curses.c -o curses -lcurses

-LC

[kristy]

Lynux-Penguin: Thank you, it compiles now.

After doing some research I'm not sure I'm on the right track. I found an example where getch() was used, and it was an application that drew a window and such in the Terminal. It also printed out 'hello' when enter was presses. All I want to do it hide the output from the Terminal (meaning that whatever's happening is not related to any specific key). Can this be done with writing the input byte-by-byte to the file? Or can really the getch() be used to hide the letters typed by the user?

The code, which is far from completed, looks like this:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <curses.h>

int main() {

    FILE *inputFile;
    char fileName[15] = "input.txt";
    char userInput[100] = { 0 };

    printf("type something: ");

    inputFile = fopen(fileName, "wa");

    if(inputFile == NULL) {
        fprintf(stderr, "aborted: NULL error while open readFile\n");
        exit(0);
    }

    // the input from the user should be hidden with something here

    fgets(userInput, sizeof(userInput), stdin);

    fwrite(userInput, 100, sizeof(char), inputFile);
    rewind(inputFile);

    fclose(inputFile);

    return 0;
}

[Lynux-Penguin]

I think you're looking for a method to un-echo the terminal.

here's an example program I wrote to use termios to disable echoing (thanks to a post made by prelude) I used it to read in a password, actually just a regular string but the point is that its hidden.

#include <termios.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

enum
{ ON, OFF };

int setEcho(int mode)
{
  struct termios tios;
  if(tcgetattr(STDIN_FILENO,&tios)!=0)
  {
    fprintf(stderr, "error on line %d, tcgetattr()\n",__LINE__-2);
    abort(); //dump the core and die
  }

  if(mode==OFF)
        tios.c_lflag &= ~(ECHO | ECHOE | ECHOK | ECHONL);
  else if(mode==ON)
        tios.c_lflag |= (ECHO | ECHOE | ECHOK | ECHONL);
  else
  {  fprintf(stderr,"invalid mode, aborting...\n"); abort(); }
  if(tcsetattr(STDIN_FILENO,TCSANOW,&tios)!=0)
  {
    fprintf(stderr, "error on line %d, tcsetattr()\n",__LINE__-2);
    abort(); //dump the core and die
  }
  return 0;
}
int main()
{
  char pass[16];
  printf("Enter pass: ");
  setEcho(OFF);
  fgets(pass,16,stdin);
  setEcho(ON);
  printf("%s\n",pass);
  return 0;
}

see, no curses ^_^

for more information on termios:

http://www.rt.com/man/termios.3.html

and http://www.faqs.org/docs/Linux-HOWTO...ing-HOWTO.html

-LC

[Draco]

try using this instead of the call to fgets().

int count=0;
char buff;

for(count=0;(buff=getch()!='\r')&&count<100;count++)
{
 userInput[count]=getch(); /*moves character to string*/
 printf("*");  /*if you want to show characters being put in*/
}

[Lynux-Penguin]

you could do it that way too, i suppose, i haven't noticed any real difference. getch essentially does the same thing as:

int getch()
{
  int c;
  setEcho(OFF); 
  c=getc(); 
  setEcho(ON);
  return c;
}

-LC

[kristy]

I'm still having some minor troubles, but you guys rock!

int count=0;
char buff;

for(count=0;(buff=getch()!='\r')&&count<100;count++)
{
 userInput[count]=getch(); /*moves character to string*/
 printf("*");  /*if you want to show characters being put in*/
}

I tried to put this in my source code instead of the fgets() line, but it didn't quite work. I got this running my program:
type something: test
************************************************** **************************************************
I guess I'm missing something vital here.. And, btw, what is this line really doing: userInput[count]=getch();
It's the []'s that confuses me.

Lynux-Penguin: Your code definitely did the job. The problem is that the code is a bit above my level, so I'll try to avoid it if I can (I don't like using code I don't understand). - But I will use it my program, ofc by giving you the proper credit, if needed. And thanks for the links, I'll be checking them out!

[Lynux-Penguin]

hey i know how you feel but the reason his code doesn't work is because his end-input exception is '\r' which I have no idea what that is, change it to '\n' and it should work fine.

the reason you get that output is because the loop just runs until 100

-LC

[Draco]

to make the asterisk's stop appearing, just remove the line

printf("*");

I only put this in because many times you enter a password it shows an asterisk instead of what you typed in. I included this in case you wanted the user to have a reference of how many characters he/she typed.

The line userInput[count] goes through each part of the userInput array and puts in the letter called by getch(). I actually wrote that line wrong, it's supposed to be

userInput[count]= buff;

I'm sorry for my mistake
It should work fine for you now

[edit]
to respond to linux-penguin's message, I may have been incorrect in giving the '/r' conditional. It has worked for me many times before, and is something I should wean myself off of
[/edit]

[kristy]

hehe, I'm kinda confused. It still doesn't work. Or, it works in the opposite way. I can type a word, which isn't entered in the file, but I want what I wrote to appear in the file (but not on the screen). Just to be sure, here's the code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <curses.h>

int main() {

    FILE *inputFile;
    char fileName[15] = "input.txt";
    char userInput[100] = { 0 };
    int count=0;
    char buff;

    printf("type something: ");

    inputFile = fopen(fileName, "wa");

    if(inputFile == NULL) {
        fprintf(stderr, "aborted: NULL error while open readFile\n");
        exit(0);
    }
    
    fgets(userInput, sizeof(userInput), stdin);
    
    for(count=0; (buff=getch()!='\n') && count < 100; count++) {
        userInput[count]= buff;		/* moves character to string*/
        printf("*");  				/* if you want to show characters being put in*/
    }

    fwrite(userInput, 100, sizeof(char), inputFile);
    rewind(inputFile);

    fclose(inputFile);

    return 0;
}

I realize I wrote something wrong in my last post. I didn't remove the fgets() line (if I do there's no way to get the input). I have tried to run the program without the fgets() line too, but it results in nothing useful. Sorry if I have confused you, I know for sure I'm confused. And, thanks for all the help so far, it's highly appreciated.

[Lynux-Penguin]

int count=0;
char buff;
char userInput[100]; /* remember to fill the full word buffer ADDED */
bool charReplace=true; /* if you want the *s to fill the input */

for(count=0;(buff=getch()!='\n')&&count<100;count++) /* '\r' -> '\n'  ADDED */
{
 userInput[count]=getch(); /*moves character to string*/  /* brilliant! */
 if(charReplace)
   printf("*");  /*if you want to show characters being put in*/
}

like this Draco?

>hehe, I'm kinda confused. It still doesn't work. Or, it works in
>the opposite way. I can type a word, which isn't entered in the
>file, but I want what I wrote to appear in the file (but not on the
>screen). Just to be sure, here's the code:

well first off you shouldn't do

fgets(str, sizeof(str), stdin);

it should be done more like:

fgets(str,strlen(str),stdin);

also I think you might want to see this:

DESCRIPTION
       The getch, wgetch, mvgetch and mvwgetch, routines  read  a
       character  from the window.  In no-delay mode, if no input
       is waiting, the value ERR is returned.  In delay mode, the
       program  waits until the system passes text through to the
       program.  Depending on the  setting  of  cbreak,  this  is
       after one character (cbreak mode), or after the first new_
       line (nocbreak mode).  In  half-delay  mode,  the  program
       waits  until a character is typed or the specified timeout
       has been reached.

and because there is nothing in the input buffer, it just returns ERR.


for a better version of getch (in my opinion)

#include <termios.h>
#include <stdio.h>
#include <unistd.h>
int vVv_getch()
{
  int ch;
  struct termios oldt,newt;
  if(tcgetattr(STDIN_FILENO,&oldt)!=0)
    return -1;
  newt = oldt;
  newt.c_lflag &= ~( ICANON | ECHO ); //disables echo and icanonical mode (no buffer)
  newt.c_cc[VMIN] = 1;
  newt.c_cc[VTIME] = 0;
  if( tcsetattr(STDIN_FILENO,TCSANOW,&newt) != 0 )
    return -1;
  ch = getchar();
  if( tcsetattr(STDIN_FILENO,TCSANOW, &oldt) != 0 )
    return -1;
  return ch;
}

for more info see the Linux board FAQ

every way I look at it your going to end up coming back to termios, unless someone can modify the terminal no_break mode without using termios... if you find a solution other than this, let me know please.


-LC