SQL-based authentication

SQL-based authentication
You are encouraged to solve this task according to the task description, using any language you may know.

This task has three parts:

• Connect to a MySQL database (connect_db)
• Create user/password records in the following table (create_user)
• Authenticate login requests against the table (authenticate_user)

This is the table definition:

create table users (
    userid int primary key auto_increment,
    username varchar(32) unique key not null,
    pass_salt tinyblob not null,  -- a string of 16 random bytes
    pass_md5 tinyblob not null
            -- binary MD5 hash of pass_salt concatenated with the password
);

(pass_salt and pass_md5 would be binary(16) values, but MySQL versions before 5.0.15 strip trailing spaces when selecting them.)

C

Library: mysqlclient

(MySQL client library)

Library: OpenSSL

(for MD5)

<lang c>#include <stdio.h>

1. include <stdlib.h>
2. include <string.h>
3. include <stdbool.h>
4. include <time.h>

1. include <mysql.h>
2. include <openssl/md5.h>

void end_with_db(void);

MYSQL *mysql = NULL; // global...

bool connect_db(const char *host, const char *user, const char *pwd, const char *db, unsigned int port) {

 if ( mysql == NULL )
 {
   if (mysql_library_init(0, NULL, NULL)) return false;
   mysql = mysql_init(NULL); if ( mysql == NULL ) return false;
   MYSQL *myp = mysql_real_connect(mysql, host, user, pwd, db, port, NULL, 0);
   if (myp == NULL) {
     fprintf(stderr, "connection error: %s\n", mysql_error(mysql));
     end_with_db();
     return false;
   }
 }
 return true; // already connected... ?

}

1. define USERNAMELIMIT 32

// no part of the spec, but it is reasonable!!

1. define PASSWORDLIMIT 32
2. define SALTBYTE 16

bool create_user(const char *username, const char *password) {

 int i;
 char binarysalt[SALTBYTE];
 char salt[SALTBYTE*2+1];
 char md5hash[MD5_DIGEST_LENGTH];
 char saltpass[SALTBYTE+PASSWORDLIMIT+1];
 char pass_md5[MD5_DIGEST_LENGTH*2 + 1];
 char user[USERNAMELIMIT*2 + 1];
 char *q = NULL;
 static const char query[] = 
   "INSERT INTO users "
   "(username,pass_salt,pass_md5) "
   "VALUES ('%s', X'%s', X'%s')";
 static const size_t qlen = sizeof query;
 

 for(i=0; username[i] != '\0' && i < USERNAMELIMIT; i++) ;
 if ( username[i] != '\0' ) return false;
 for(i=0; password[i] != '\0' && i < PASSWORDLIMIT; i++) ;
 if ( password[i] != '\0' ) return false;

 srand(time(NULL));

 for(i=0; i < SALTBYTE; i++)
 {
   // this skews the distribution but it is lazyness-compliant;)
   binarysalt[i] = rand()%256; 
 }

 (void)mysql_hex_string(salt, binarysalt, SALTBYTE);
 
 for(i=0; i < SALTBYTE; i++) saltpass[i] = binarysalt[i];
 strcpy(saltpass+SALTBYTE, password);
 (void)MD5(saltpass, SALTBYTE + strlen(password), md5hash);
 (void)mysql_hex_string(pass_md5, md5hash, MD5_DIGEST_LENGTH);

 (void)mysql_real_escape_string(mysql, user, username, strlen(username));

 // salt, pass_md5, user are db-query-ready
 q = malloc(qlen + USERNAMELIMIT*2 + MD5_DIGEST_LENGTH*2 + SALTBYTE*2 + 1);
 if ( q == NULL ) return false;
 sprintf(q, query, user, salt, pass_md5);

1. if defined(DEBUG)

 fprintf(stderr, "QUERY:\n%s\n\n", q);

1. endif

 int res = mysql_query(mysql, q);
 free(q);
 if ( res != 0 )
 {
   fprintf(stderr, "create_user query error: %s\n", mysql_error(mysql));
   return false;
 }
 return true;

}

bool authenticate_user(const char *username, const char *password) {

 char user[USERNAMELIMIT*2 + 1];
 char md5hash[MD5_DIGEST_LENGTH];
 char saltpass[SALTBYTE+PASSWORDLIMIT+1];
 bool authok = false;
 char *q = NULL;
 int i;
 static const char query[] = 
   "SELECT * FROM users WHERE username='%s'";
 static const size_t qlen = sizeof query;

 // can't be authenticated with invalid username or password
 for(i=0; username[i] != '\0' && i < USERNAMELIMIT; i++) ;
 if ( username[i] != '\0' ) return false;
 for(i=0; password[i] != '\0' && i < PASSWORDLIMIT; i++) ;
 if ( password[i] != '\0' ) return false;

 (void)mysql_real_escape_string(mysql, user, username, strlen(username));  

 q = malloc(qlen + strlen(user) + 1);
 if (q == NULL) return false;
 sprintf(q, query, username);

 int res = mysql_query(mysql, q);
 free(q);
 if ( res != 0 )
 {
   fprintf(stderr, "authenticate_user query error: %s\n", mysql_error(mysql));
   return false;
 }

 MYSQL_RES *qr = mysql_store_result(mysql);
 if ( qr == NULL ) return false;

 // should be only a result, or none
 if ( mysql_num_rows(qr) != 1 ) {
   mysql_free_result(qr);
   return false;
 }

 MYSQL_ROW row = mysql_fetch_row(qr);          // 1 row must exist
 unsigned long *len = mysql_fetch_lengths(qr); // and should have 4 cols...

 memcpy(saltpass, row[2], len[2]); // len[2] should be SALTBYTE
 memcpy(saltpass + len[2], password, strlen(password));
 (void)MD5(saltpass, SALTBYTE + strlen(password), md5hash);

 authok = memcmp(md5hash, row[3], len[3]) == 0;
 mysql_free_result(qr);

 return authok;

}

void end_with_db(void) {

 mysql_close(mysql); mysql = NULL;
 mysql_library_end();

}

int main(int argc, char **argv) {

 if ( argc < 4 ) return EXIT_FAILURE;

 if ( connect_db("localhost", "devel", "", "test", 0 ) )
 {
   if ( strcmp(argv[1], "add") == 0 )
   {
     if (create_user(argv[2], argv[3])) 

printf("created\n");

   } else if ( strcmp(argv[1], "auth") == 0 ) {
     if (authenticate_user(argv[2], argv[3]))

printf("authorized\n");

     else

printf("access denied\n");

   } else {
     printf("unknown command\n");
   }
   end_with_db();
 }
 return EXIT_SUCCESS;

}</lang>

From the command line, program add user password to add users, and program auth user password to see if the user with that password is authorized or not.

Perl

Works with: Perl version 5.8.8

Library: DBI

Library: DBD::mysqlmysql

<lang perl>use DBI;

# returns a database handle configured to throw an exception on query errors

sub connect_db {

   my ($dbname, $host, $user, $pass) = @_;
   my $db = DBI->connect("dbi:mysql:$dbname:$host", $user, $pass)
       or die $DBI::errstr;
   $db->{RaiseError} = 1;
   $db

}

# if the user was successfully created, returns its user id.
# if the name was already in use, returns undef.

sub create_user {

   my ($db, $user, $pass) = @_;
   my $salt = pack "C*", map {int rand 256} 1..16;
   $db->do("INSERT IGNORE INTO users (username, pass_salt, pass_md5)
       VALUES (?, ?, unhex(md5(concat(pass_salt, ?))))",
       undef, $user, $salt, $pass)
     and $db->{mysql_insertid} or undef

}

# if the user is authentic, returns its user id.  otherwise returns undef.

sub authenticate_user {

   my ($db, $user, $pass) = @_;
   my $userid = $db->selectrow_array("SELECT userid FROM users WHERE
       username=? AND pass_md5=unhex(md5(concat(pass_salt, ?)))",
       undef, $user, $pass);
   $userid

}</lang>

PHP

To use MySQL in PHP you need the php_mysql module installed <lang php> function connect_db($database, $db_user, $db_password, $host = 'localhost', $port = NULL, $die = false) { // Returns a MySQL link identifier (handle) on success // Returns false or dies() on error depending on the setting of parameter $die // Parameter $die configures error handling, setting it any non-false value will die() on error // Parameters $host, $port and $die have sensible defaults and are not usually required

if(!$db_handle = @mysql_connect($host.($port ? ':'.$port : ), $db_user, $db_password)) { if($die) die("Can't connect to MySQL server:\r\n".mysql_error()); else return false; } if(!@mysql_select_db($database, $db_handle)) { if($die) die("Can't select database '$database':\r\n".mysql_error()); else return false; } return $db_handle; }

function create_user($username, $password, $db_handle) { // Returns the record ID on success or false on failure // Username limit is 32 characters (part of spec) if(strlen($username) > 32) return false;

// Salt limited to ASCII 32 thru 254 (not part of spec) $salt = ; do { $salt .= chr(mt_rand(32, 254)); } while(strlen($salt) < 16);

// Create pass_md5 $pass_md5 = md5($salt.$password);

// Make it all binary safe $username = mysql_real_escape_string($username); $salt = mysql_real_escape_string($salt);

// Try to insert it into the table - Return false on failure if(!@mysql_query("INSERT INTO users (username,pass_salt,pass_md5) VALUES('$username','$salt','$pass_md5')", $db_handle)) return false;

// Return the record ID return mysql_insert_id($db_handle); }

function authenticate_user($username, $password, $db_handle) { // Checks a username/password combination against the database // Returns false on failure or the record ID on success

// Make the username parmeter binary-safe $safe_username = mysql_real_escape_string($username);

// Grab the record (if it exists) - Return false on failure if(!$result = @mysql_query("SELECT * FROM users WHERE username='$safe_username'", $db_handle)) return false;

// Grab the row $row = @mysql_fetch_assoc($result);

// Check the password and return false if incorrect if(md5($row['pass_salt'].$password) != $row['pass_md5']) return false;

// Return the record ID return $row['userid']; } </lang>

Python

This example is in need of improvement: This example is missing proper encoding or bound parameters to avoid SQL injection, which are present in the other examples. In general is is an unsafe practice to create sql commands directly with string operations

<lang python>with Python 2.6, gives a deprecation warning for sets module, but works import MySQLdb import hashlib

import sys import random

DB_HOST = "localhost" DB_USER = "devel" DB_PASS = "" DB_NAME = "test"

def connect_db():

    Try to connect DB and return DB instance, if not, return False 	 
   try:	 
       return MySQLdb.connect(host=DB_HOST, user=DB_USER, passwd=DB_PASS, db=DB_NAME)	 
   except:	 
       return False	 

def create_user(username, passwd):

    if user was successfully created, returns its ID 	 
   db = connect_db()	 
   if not db:	 
       print 'Can\'t connect MySQL!'	 
       sys.exit(1)	 

   cursor = db.cursor()	 

   salt = randomValue(16)	 	 
   passwd_md5 = hashlib.md5(salt+passwd).hexdigest()	 

   # If username already taken, inform it	 
   try:	 
       cursor.execute("INSERT INTO users (`username`, `pass_salt`, `pass_md5`) VALUES ('%s', '%s', '%s')" % (username, salt, passwd_md5)) 
       cursor.execute("SELECT userid FROM users WHERE username='%s'" % username) 
       id = cursor.fetchall()	 
       return id[0][0]	 
   except:	 
       print 'Username was already taken. Please select another'	 
       sys.exit(1)	 

def authenticate_user(username, passwd):

   db = connect_db()	 
   if not db:	 
       print 'Can\'t connect MySQL!'	 
       sys.exit(1)	 

   cursor = db.cursor()	 

   try:
       scheck = cursor.execute("SELECT pass_salt FROM users WHERE username='%s'" % (username))
   except:
       return False

   if scheck == 0:
       return False

   salt = cursor.fetchone()[0]
   passwd = hashlib.md5(salt+passwd).hexdigest()	 

   # cursor returns 1 if query is successfull else it returns 0	 
   user = cursor.execute("SELECT userid, username FROM users WHERE username='%s' AND pass_md5='%s'" % (username, passwd))	 
   if user != 0:	 
       return True	 
   else:	 
       return False	 

def randomValue(length):

    Creates random value with given length	 
   salt_chars = 'abcdefghijklmnopqrstuvwxyz0123456789'	 
   output = ""	 

   for x in range(length):	 
       rand = random.randrange(0, 35)	 
       output = output + salt_chars[rand]	 

   return output	 

if __name__ == '__main__':

   user = randomValue(10)	 
   passwd = randomValue(16)	 

   create_user(user, passwd)	 
   auth = authenticate_user(user, passwd)	 
   if auth:	 
       print 'User %s authenticated successfully' % user	 
   else:	 
       print 'User %s failed' % user</lang>

Raven

MySQL connectivity is available out of the box. Below, we do not ever send the plain text password over the wire.

<lang raven> 'mysql://root@localhost/test' open as mysql 'abcdefghijklmnopqrstuvwxyz0123456789' as $salt_chars

1. return userid for success and FALSE for failure.

define create_user use $user, $pass

   group 16 each as i
       $salt_chars choose chr
   join as $pass_salt
    "%($pass_salt)s%($pass)s" md5 as $pass_md5
   $user copy mysql escape as $user_name
   group 'INSERT IGNORE into users (username, pass_md5, pass_salt)'
       " VALUES ('%($user_name)s', unhex('%($pass_md5)s'), '%($pass_salt)s')"
   join mysql query inserted

1. return userid for success and FALSE for failure.

define authenticate_user use $user, $pass

   FALSE as $userid
   $user copy mysql escape as $user_name
   group 'SELECT userid, pass_salt, hex(pass_md5)'
       " FROM users WHERE username = '%($user_name)s'"
   join mysql query as rs
   rs selected
   if  rs fetch values into $possible_userid, $pass_salt, $pass_md5
       "%($pass_salt)s%($pass)s" md5 $pass_md5 lower =
       if  $possible_userid as $userid
   $userid

'foo' 'bar' create_user !if "could not create user\n" print bye 'foo' 'bar' authenticate_user !if "could not authenticate user\n" print bye

"user successfully created and authenticated!\n" print</lang>

Tcl

Works with: Tcl version 8.6

Also requires the TDBC driver for MySQL. <lang Tcl>package require tdbc

proc connect_db {handleName dbname host user pass} {

   package require tdbc::mysql
   tdbc::mysql::connection create $handleName -user $user -passwd $pass \
       -host $host -database $dbname
   return $handleName

}

1. A simple helper to keep code shorter

proc r64k {} {

   expr int(65536*rand())

}

proc create_user {handle user pass} {

   set salt [binary format ssssssss \
       [r64k] [r64k] [r64k] [r64k] [r64k] [r64k] [r64k] [r64k]]
   # Note that we are using named parameters below, :user :salt :pass
   # They are bound automatically to local variables with the same name
   $handle allrows {
       INSERT IGNORE INTO users (username, pass_salt, pass_md5)
           VALUES (:user, :salt, unhex(md5(concat(:salt, :pass))))
   }
   return   ;# Ignore the result of the allrows method

}

proc authenticate_user {handle user pass} {

   $handle foreach row {
       SELECT userid FROM users WHERE
           username=:user AND pass_md5=unhex(md5(concat(pass_salt, :pass)))
   } {
       return [dict get $row userid]
   }
   # Only get here if no rows selected
   error "authentication failed for user \"$user\""

}</lang> Template:Omit from PostScript