check Linux password from /etc/shadow

htabesh · 10-30-2008, 04:37 PM

Hi,
I want to write a C Program that get a password and user name, then compare it with encrypted password in /etc/shadow.
Please help me with SIMPLE CODES.

chrism01 · 10-30-2008, 06:28 PM

Have a look here:
man crypt

bgeddy · 10-30-2008, 08:42 PM

There's some simple examples here

htabesh · 10-31-2008, 04:49 AM

I try below program:

Code:

#define _XOPEN_SOURCE
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <crypt.h>

int main (void)
{
	char *passwd;
	passwd = crypt("123456", "$1$yfKCUYj6");

}

And then compile that:

Code:

gcc 1.c -o 1

The out put of compile is:

Code:

/tmp/cci2MSHh.o: In function `main':
1.c:(.text+0x21): undefined reference to `crypt'
collect2: ld returned 1 exit status

What is the problem?

keefaz · 10-31-2008, 08:20 AM

try add -lcrypt in the gcc command line

htabesh · 10-31-2008, 08:55 AM

OK, thanks.
Now how can I write a C Program that get a password and user name, then compare it with encrypted password in /etc/shadow for authentication?

nishamathew1980 · 11-02-2008, 04:58 AM

@ bgeddy,
That was an interesting and informative article. Thanks for posting it here.

Linux Archive

htabesh · 11-04-2008, 08:12 AM

Finally I found the way.

Code:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <crypt.h>
int main(int argc, char *agrv[])
{
	const char *const pass = "$1$Og9RbNrT$/gNprNaDgv.hNS01Ue2gi1";
    	char *result;
        int ok;
        result = crypt(getpass("Password:"), pass);
        ok = strcmp (result, pass);
        if ( ok == 0 )
	{
        	puts("Access granted"\n);
		return 0;
	}
        else 
	{
	        puts ("Access denied\n");
		return 1;
	}
}

you can find and replace salt ("pass" in this program) in /etc/shadow for any user.
e.g.:
root:$1$Og9RbNrT$/gNprNaDgv.hNS01Ue2gi1:14159:0:99999:7:::

Keith Hedger · 05-24-2013, 12:44 PM

Thanks for this I've been trying a number of different example and this is the first that worked.
P.S. one minor typo "puts("Access granted"\n);" should be puts("Access granted\n");