1. PHP Security

3. Two Golden Rules PHP Script Filter Escape Cookie Forms Referer, etc. xhtml MYSQL

5. Filter example $clean = array (); if ( ctype_alnum ($_POST[ 'username' ])) { $clean[ 'username' ] = $_POST[ 'username' ]; }

6. Filter example $clean = array (); if ( ctype_alnum ($_POST[ 'username' ])) { $clean[ 'username' ] = $_POST[ 'username' ]; } $clean = array (); Initialise an array to store filtered data.

7. Filter example $clean = array (); if ( ctype_alnum ($_POST[ 'username' ])) { $clean[ 'username' ] = $_POST[ 'username' ]; } if ( ctype_alnum ($_POST[ 'username' ])) Inspect username to make sure that it is alphanumeric.

8. Filter example $clean = array (); if ( ctype_alnum ($_POST[ 'username' ])) { $clean[ 'username' ] = $_POST[ 'username' ]; } $clean[ 'username' ] = $_POST[ 'username' ]; If it is, store it in the array.

10. Escape example $xhtml = array (); $xhtml[ 'username' ] = htmlentities ($clean[ 'username' ], ENT_QUOTES , 'UTF-8' ); echo &quot;<p>Welcome back, {$xhtml[ 'username' ]} .</p>&quot; ;

11. Escape example $xhtml = array (); $xhtml[ 'username' ] = htmlentities ($clean[ 'username' ], ENT_QUOTES , 'UTF-8' ); echo &quot;<p>Welcome back, {$xhtml[ 'username' ]} .</p>&quot; ; $xhtml = array (); Initialize an array for storing escaped data.

12. Escape example $xhtml = array (); $xhtml[ 'username' ] = htmlentities ($clean[ 'username' ], ENT_QUOTES , 'UTF-8' ); echo &quot;<p>Welcome back, {$xhtml[ 'username' ]} .</p>&quot; ; $xhtml[ 'username' ] = htmlentities ($clean[ 'username' ], ENT_QUOTES , 'UTF-8' ); Escape the filtered username, and store it in the array.

13. Escape example $xhtml = array (); $xhtml[ 'username' ] = htmlentities ($clean[ 'username' ], ENT_QUOTES , 'UTF-8' ); echo &quot;<p>Welcome back, {$xhtml[ 'username' ]} .</p>&quot; ; echo &quot;<p>Welcome back, {$xhtml[ 'username' ]} .</p>&quot; ; Send the filtered and escaped username to the client.