15.c

 

#include <stdio.h>
#define _XOPEN_SOURCE
#include <unistd.h>
#include <shadow.h>
#define BUFSIZE 1024
int main(int argc, char *argv[])
{
    char buf[BUFSIZE];
    struct spwd *sp;
    char *enc;
    if (argc < 2)
    {
        fprintf(stderr, "Usage: ...\n");
        return -1;
    }
    printf("Username: %s\n", argv[1]);
    printf("Password: ");
    scanf("%s", buf);
    sp = getspnam(argv[1]);
    if (sp == NULL)
    {
        perror("getspname");
        return -1;
    }
    printf("sp->sp_pwdp = %s\n", sp->sp_pwdp);
    printf("buf = %s\n", buf);
    enc = crypt(buf, sp->sp_pwdp);
    printf("enc = %s\n", enc);
    if (strcmp(enc, sp->sp_pwdp) == 0)
    {
        printf("Yes!\n");
    }
    else
    {
        printf("No!\n");
    }
    return 0;
}