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valid.c

/*
 * Copyright 1989 - 1993, Julianne Frances Haugh
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Julianne F. Haugh nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include "rcsid.h"
RCSID("$Id: valid.c 6 2005-03-20 15:34:28Z bubulle $")

#include <sys/types.h>
#include <stdio.h>
#include "prototypes.h"
#include "defines.h"
#include <pwd.h>

/*
 * valid - compare encrypted passwords
 *
 *    Valid() compares the DES encrypted password from the password file
 *    against the password which the user has entered after it has been
 *    encrypted using the same salt as the original.  Entries which do
 *    not have a password file entry have a NULL pw_name field and this
 *    is used to indicate that a dummy salt must be used to encrypt the
 *    password anyway.
 */

int
valid(const char *password, const struct passwd *ent)
{
      const char *encrypted;
      const char *salt;

      /*
       * Start with blank or empty password entries.  Always encrypt
       * a password if no such user exists.  Only if the ID exists and
       * the password is really empty do you return quickly.  This
       * routine is meant to waste CPU time.
       */

      if (ent->pw_name && ! ent->pw_passwd[0]) {
            if (! password[0])
                  return (1); /* user entered nothing */
            else
                  return (0); /* user entered something! */
      }

      /*
       * If there is no entry then we need a salt to use.
       */

      if (ent->pw_name == (char *) 0 || ent->pw_passwd[0] == '\0') {
            salt = "xx";
      } else {
            salt = ent->pw_passwd;
      }

      /*
       * Now, perform the encryption using the salt from before on
       * the users input.  Since we always encrypt the string, it
       * should be very difficult to determine if the user exists by
       * looking at execution time.
       */

      encrypted = pw_encrypt(password, salt);

      /*
       * One last time we must deal with there being no password file
       * entry for the user.  We use the pw_name == NULL idiom to
       * cause non-existent users to not be validated.
       */

      if (ent->pw_name && strcmp(encrypted, ent->pw_passwd) == 0)
            return (1);
      else
            return (0);
}

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