CaptchaPlugin

A visual confirmation plugin, known as Captcha, for new user registration. This plugin prevents automated scripts in creating users and spam your wiki with their url's to get a better google ranking.

Syntax Rules

• The tag %CAPTCHAURL% expands to the url of the image containing the scrambled text;
• The tag %CAPTCHAHASH% expands to the hash matching the image.

Plugin Settings

Plugin settings are stored as preferences variables. To reference a plugin setting write %<plugin>_<setting>%, i.e. %INTERWIKIPLUGIN_SHORTDESCRIPTION%

• One line description, is shown in the TextFormattingRules topic:
  • Set SHORTDESCRIPTION = To prevent automated bots from spamming

• Debug plugin: (See output in data/debug.txt)
  • Set DEBUG = 0

Additionally, the following settings can be changed in lib/LocalSite.cfg, the list below shows the defaults.

• $TWiki::cfg{Plugins}{CaptchaPlugin}{Expiry} = 3600; # Time in seconds after which a Captcha will expire and be removed
• $TWiki::cfg{Plugins}{CaptchaPlugin}{EnableSave} = 0; # Enable Captcha for topic save
• $TWiki::cfg{Plugins}{CaptchaPlugin}{SaveForAll} = 0; # Enable Captcha for all users, not just TWikiGuest
• $TWiki::cfg{Plugins}{CaptchaPlugin}{DeleteAfterSave} = 0; # Delete Captcha after successful topic save
• $TWiki::cfg{Plugins}{CaptchaPlugin}{ColourSafe} = 0; # Enable for black and white shades only
• $TWiki::cfg{Plugins}{CaptchaPlugin}{NumberOfCharacters} = 5; # Number of characters on Captcha
• $TWiki::cfg{Plugins}{CaptchaPlugin}{Characters} = '1234567890'; # Captcha characters, numbers are the safest

Plugin Installation Instructions

Note: You do not need to install anything on the browser to use this plugin. The following instructions are for the administrator who installs the plugin on the server where TWiki is running.

• Download the ZIP file from the Plugin web (see below)
• Unzip CaptchaPlugin.zip in your twiki installation directory. Content:

  File:	Description:
  data/TWiki/CaptchaPlugin.txt,v	Plugin topic repository
  data/TWiki/CaptchaPlugin.txt	Plugin topic
  lib/TWiki/Plugins/CaptchaPlugin.pm	Plugin Perl module
  Register.pm-4.1.2.patch	Patch for the register module
  edit.pattern.tmpl-4.1.2.patch	Patch for Pattern
  edittoolbar.nat.tmpl-3.0-pre13.patch	Patch for NatSkin
  pub/TWiki/CaptchaPlugin/img	Image directory
  pub/TWiki/CaptchaPlugin/_db	Hash database directory
  templates/oopscaptcha.tmpl	Error template
  templates/editcaptcha.tmpl	Edit template
  pub/TWiki/CaptchaPlugin/fonts/*	A collection of free fonts to get you started

• Apply the patch Register.pm-4.1.2.patch to lib/TWiki/UI/Register.pm (alternatively, patch Register.pm manually, see section below), be sure to make a backup so you can revert the patch if you want to disable the plugin:
  • cd /path/to/twiki
  • cp lib/TWiki/UI/Register.pm lib/TWiki/UI/Register.pm.dist
  • patch < ../register.patch
• Restrict access to the files, for example, by including the following in your httpd.conf:

         <Directory "/path/to/twiki/pub/TWiki/CaptchaPlugin/_db">
           deny from all
         </Directory>
         <Directory "/path/to/twiki/pub/TWiki/CaptchaPlugin/fonts">
           deny from all
         </Directory>

• Enable the plugin via the bin/configure script
• Install necessary TrueType fonts in to pub/TWiki/CaptchaPlugin/fonts/
  • This allows the plugin to randomly choose the fonts to use
  • The more you have, the higher the chances of fending off spambots
• Test if the installation was successful:
  • Create a topic containing <IMG SRC="%CAPTCHAURL%"> and %CAPTCHAHASH%
  • When loading this topic you should see an obfuscated character string loaded as a png and a hexadecimal hash.
  • Check whether the hash database is properly protected by going to the url http://my.twiki.server/my/twiki/path/pub/TWiki/CaptchaPlugin/db/hashes.pag, you should see a permission denied message.
• Now edit your TWikiRegistration topic
  • Display the image %CAPTCHAURL% somewhere in your form, along with a text instructing new users to copy the obfuscated text into the appropriate text input.
  • Add the appropriate text input as Twk1CaptchaString
  • Add a hidden input as Twk1CaptchaHash having as value %CAPTCHAHASH%
  • For example, add this to your TWikiRegistration:

            <tr>
              <td valign="top" align="right"><IMG SRC="%CAPTCHAURL%">: <br /> (..)   </td>
              <td><input type="hidden" name="Twk1CaptchaHash" value="%CAPTCHAHASH%">
                  <input type="text" name="Twk1CaptchaString" size="5"></td>  =<font color="red">**</font>=
            </tr>

• That's it.

Captcha on topic edit

If you want to protect edits by TWikiGuest with a captcha, add the following line to your lib/LocalSite.cfg:

$TWiki::cfg{Plugins}{CaptchaPlugin}{EnableSave} = 1;

A editcaptcha.tmpl has been prepared for you. All you need to do is TMPL:INCLUDE it into your edit*.tmpl. Two patches are available for Pattern (edit.pattern.tmpl) and NatSkin (edittoolbar.nat.tmpl).

At the moment, editcaptcha.tmpl requires TWiki:Plugins.IfDefinedPlugin to determine whether the user is TWikiGuest? or not. If you have enabled $TWiki::cfg{Plugins}{CaptchaPlugin}{SaveForAll} = 1;, modify editcaptcha.tmpl appropriately.

Manually patching the register binary

Refer to the patch file.

Guide for TWiki 4.0.5

 }
 
 # generate user entry

Insert the code below directly BEFORE the line containing the curly bracket '{':

    # verify captcha
    eval { use TWiki::Plugins::CaptchaPlugin; };

    my %database;
    my $vcHash = $data->{CaptchaHash};
    my $vcTxt = $data->{CaptchaString};

    open(LOCKFILE,">".&TWiki::Func::getPubDir()."/TWiki/CaptchaPlugin/_db/hashes.lock");
    flock(LOCKFILE,2);

    dbmopen(%database, &TWiki::Func::getPubDir()."/TWiki/CaptchaPlugin/_db/hashes",0644);

    my ($time,$txt) = split(',',$database{$vcHash});

    if ( not(lc($txt) eq lc($vcTxt)) || ($txt eq '') ) {
                dbmclose(%database);
                close(LOCKFILE);
                throw TWiki::OopsException( 'captcha',
                                           web => $data->{webName},
                                       topic => $topic,
                                       def => 'invalid_vcstr',
                                       params => [ "wrong" ] );
    }

    dbmclose(%database);

    close(LOCKFILE);

        TWiki::Plugins::CaptchaPlugin::expire($vcHash);

Now find:

             # 'WikiName' omitted because they can't
             # change it, and 'Confirm' is a duplicate
             push( @{$data->{form}}, $form )
              unless ($name eq 'WikiName' || $name eq 'Confirm');

and change the last line to:

             # 'WikiName' omitted because they can't
             # change it, and 'Confirm' is a duplicate
             push( @{$data->{form}}, $form )
              unless ($name eq 'WikiName' || $name eq 'Confirm' || $name eq 'CaptchaHash' || $name eq 'CaptchaString');

Further Development

• Refactor to comply with TWiki's convention
• Adjustable font size range
• Adjustable height and width

Plugin Info

Related Topics: TWikiPreferences, TWikiPlugins