Create salted MD5 passwort for /etc/shadow

Chris Sandrini
Chris Sandrini used Ask the Experts™
on
Hi

I am trying to generate a salted md5 hash in C with the propper format "$1$salt$hash" for the /etc/shadow file.

I am not quite sure if $1$ should be part of the salt or not? Right now I use the following code to generate a salt and create the passwort using crypt()

char salt[9];
  char full[50];

  int i = 0;
  static char *choices = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
                         "0123456789./";

  for(i = 0; i<8; i++)
  {
    salt[i] = choices[random_in_range(0, strlen(choices) - 1)];
  }
  salt[8] = 0;

  sprintf(full,"$1$%s",salt);

  /* Loop thru passwd file */
  char pw[100];

  sprintf(pw,"$1$%s$%s",salt,crypt(password, full));

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Any hint would be great!
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Senior System Engineer
Top Expert 2012
Commented:
Nevermind. I found a solution to even create SHA-512 passwords. This is my code

int setPassword(const char *password)
{
  FILE* fps;

  struct spwd *sp;
  memset(&sp, 0, sizeof(sp));

  if (!(fps = fopen("/etc/shadow", "r+"))) {
    return 0;
  }

  char user[20] = "amber";
  char salt[9];
  char full[50];

  int i = 0;
  static char *choices = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
                         "0123456789./";

  for(i = 0; i<8; i++)
  {
    salt[i] = choices[random_in_range(0, strlen(choices) - 1)];
  }
  salt[8] = 0;

  sprintf(full,"$6$%s",salt);

  /* Loop thru passwd file */
  char pw[100];

  sprintf(pw,"%s",crypt(password, full));



  while ((sp = getspent()) != NULL) {
    if (strcmp(sp->sp_namp,user) == 0 ) {
      strcpy(sp->sp_pwdp,pw);
      putspent(sp, fps);
    } else {
      putspent(sp,fps);
    }
  }

  fclose(fps);

  return 1;
}

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