John Kr is a small business owned by Elger Jonker, an ethical hacker from The Netherlands.

I’m currently active in organizing MCH2022, python development for internet.nl, basisbeveiliging.nl and various other projects. I also perform web-pentests at irregular intervals for applications that contain sensitive (medical) data.

All information below is severely outdated, because time and reasons.

You can contact me at elger@…




The (outdated :)) portfolio of a hacker




One of my radio interviews about Awesome Retro, a foundation i’ve built from the ground up. I’ve done multiple radio interviews about both my work as an ethical hacker, as well as the projects i’ve started.

Picture by Studio Brussel






Conference Speaker

twilight elger jonker

Twilight-CD @ OHM2013

Media Archeology: Dissecting an extremely popular monthly software series “Twilight”. Making millions, a strong brand, and not getting caught. This is what i found out dissecting the most beautifully designed illegal software series in the Netherlands.

The picture shows that scratching out a hologram does not work.

View the presentation: https://www.youtube.com/watch?v=A8U7qnI6ngw




Session Management @ EMF2014

EMF2014 was a hacker conference in the United Kingdom. My lecture was about developing perfect session management in privacy sensitive web applications. All Dutch speakers wore Orange suits to represent The Netherlands in an awfully tacky way.

Watch the talk: https://www.youtube.com/watch?v=-kEhvoS6HV0




Community Building @ OpenSuse2015

Community building at nerd level difficulty. The only question that you need to ask yourself is “why”, a concept introduced by Simon Sinek. Applying this logic to OpenSuse (and many others), i could not find why i would like to join it… which is a challenge for this community. Best part after 10:00.

Watch the talk: https://www.youtube.com/watch?v=odEwPM-u7cg




Mediawiki Development

Pushing MediaWiki to it’s limits with Semantic Mediawiki and custom innovations has helped many hackerspaces in the Netherlands to showcase their projects, having a better overview of their data and having to learn fewer to no syntax to get great results.

I believe that the right approach is to “applicationize” datasets, without imposing too much rules on the data itself. It has proven to work with hackers.






Mediawiki innovations


Projects Showcase

Any hackerspace has a lot of projects going on. To show what is happening at Hack42, a project page has been created, together with a list of projects. The list shows images of projects and allow multiple users per project. The projects are presented polaroid style.

This approach has been copied to other wiki’s such as the hackerspace Nurdspace.




Mentioned Users

With the {{MentionedUser|username}} template, information from the userpage is retrieved. It shows the profile image, projects and interests of the user. This template helps getting to know the members at Hack42.

This approach has been copied to other wikis, such as the Hackerspace Frack wiki.




Built with MediaWiki


Team Overview

This dynamic overview allows teams to specify the number of members they need and shows who are the first line contacts.




Team Meetings

Teams can plan meetings in the wiki, which are placed on a calendar and syndicated to rss and ical.




Navigation Boxes

The bottom of a series of pages contains this navigation menu. It is a lightweight clone of the official menu of Wikipedia, without the need for the LUA scripting environment. It is built with CSS and wiki-syntax. No plugins or javascript needed.





User Page

User pages contain a picture, interests, projects and other information placed on the wiki by a user. They are meant to be colorful and engaging.




Member list

The memberlist shows profile pictures and barcodes to be used at the Hack42 bar for purchasing products.




Activities list

Activities are available in iCal, RSS and on the wiki.





Instructions help new wiki-users to create pages in a coherent fashion. The guide explains what to enter where.






Forms make it easy to fill in information, reducing a common anti-pattern called stonewalling: forcing new and enthusiastic users to read 40 pages of bureaucracy.





Statistics can be derived from every aspect of a wiki. From the built-in statistics to custom statistics, shown here are numbers of projects, tools and more.




Side Menus

Side menus are ideal for navigation through a chapter. It is comparable to an index.




MediaWiki Management



SHA2017 is managed by statistics, which are gathered through the wiki. It is team-focussed and helps teams sharing information about vacancies and meetings. The whole world can see how a team is doing, which is a core value of SHA: transparency.






This wiki featured community news, just as the CCC2011 wiki did. It included a list of projects similar to Hack42.

https://ohm2013.org/wiki/ (offline)





Hack42 was in need of an information sharing structure. Together with a fried we made the wiki usable, with lot’s of activities and projects to discover.







  • Four private, corporate, wiki’s.
  • Frontpage of the CCC-2011 Camp wiki (as seen above).



Participation in Hacker conferences

Hacker conferences push the limit of technology, while being very social. It is targeted at a special kind of people that is deeply invested in technology and the progress of humanity.

I’ve participated in hacker conferences as both visitor, volunteer and leader. My first one was NE2000 in 2002, from then HAR2009, Eth0, Hacker Hotel, DEFCON 23, 27C3, 29C3 to 32C3, OHM2013, SHA2017, MCH2021, Hack in the Box 2010 – now. 

Hacker conferences provide an inviting atmosphere to help and make the event great for everyone.

Picture: OHM2013 campsite by Ruben van Staveren






Impact on the conferences



For SHA2017 i’ve initiated the project-management team dubbed the “Sanity” or “Projectleiding” team. This team has the main goal to organize this conference while being still able to have fun before, during and after the event. Our strategy is based on team redundancy and communication.



At OHM2013 i’ve been involved in producing Rainbow Island, a 2500 square meter gaming paradise. Additionally i’ve designed various scaffolding constructions, helped build their web-presence and have done various other things.





Hacker Hotel

A friend wanted to start a new hacker conference called “Hacker Hotel”. Together we’ve setup a wordpress site and worked out the concept. This is a yearly event in the Netherlands.

Picture: Hotel Overbosch, Garderen




Board membership of foundations





IFCAT Foundation

Responsible for SHA2017, MCH2021 / MCH2022.


Internet Cleanup Foundation



Awesome Retro

I’ve founded the Awesome Retro foundation from scratch. Continuous and limitless dedication resulted in a group of friends that shared the same goal: retrogaming for everyone. It today visits the biggest festivals in all kinds of genres to bring retrogaming. It also has a public retro-gaming community location called Awesome Space. I’m proud to say that this foundation has made an impact on over half a million people in the Netherlands.

I’ve left the foundation in November 2015 to focus on security, ethical hacking and giving myself space to discover new frontiers.






After the HAR2009 conference, hackerspaces started popping up in the Netherlands. First RandomData, then RevSpace. All i knew is that i had to do this. I jumped on board at the idea of Hack42, where i was the treasurer, helped with practical operations such as finding a location and set up policy.

I left Hack42 after two years to take care of the Awesome Retro foundation.



Media Archeology




A closeup of a Twilight Warez CD. I’ve dissected multiple collections from the nineties, a time prior to the internet. Everything that could be documented was documented, resulting in insanely large catalogs of information.  They now serve as the go-to places for these subjects and have contributed to wikipedia articles on the subjects.






Twilight CD

In the Netherlands, before the age of internet, software piracy was done on physical media. The largest and highest quality production was Twilight-CD, which ran for years on end, with millions of copies sold. I’ve dissected this compilation, from artwork to bits and bytes on the cd-rom. It was featured on GeenStijl and is the leading resource on software piracy in The Netherlands. This research started after purchasing the domain, previously owned by the Twilight crew.




flippo 1


Flippo’s (tazos, pogs) was the biggest collecting craze ever hitting the Netherlands. With 97% of all children collecting these disks, it was a major commercial success. I’ve collected everything i could find and published it on a website. As usual, this research goes to extreme lengths and has identified the majority of anything that was ever known about the Flippo.

The picture shows a sticker intended to be on the bag of crisps. http://flippos.info




Rave Radio

Rave Radio was a house radio show on Dutch public broadcast between 1992 and 1995 presented by Adam Curry and mixed by Ronald Molendijk. Me and and Ruud van der Klugt revived this show with a few episodes of our own and by digitizing hundreds of cassettes.

All episodes can now be listened to on YouTube, it truly is the golden era of house music.

The picture is a re-creation by Ruud of the original and obscure Rave Radio logo. We did not get permission of Veronica to publish it, so we used the anagram “Rave Icon”. http://raveradio.nl/





Greenpoint / CT2

Greenpoint was the commercial name for the CT2 network. It was a predecessor of GSM and allowed for wireless calling near a base station. Me and Sjors Gielen have collected a lot of greenpoint material including handsets, booklets, flyers and newspaper articles. We’ve placed everything online. The only working GreenPoint base station in the world is situated at Hackerspace Hack42.





My first research endeavor was into the Braun MTV Eurochart music cd’s. This was a brand of pirated music discs containing a selection of chart-hits. They where produced and sold illegally by the ten-thousands each month. 

http://elgerjonker.nl (contains these articles, they will be moved to a separate site for clarity.)




Software development





Hacking tools



Safehash calculates hash values of any data given, while not sending it to a server. It is written in Javascript and has a cool and unique party-mode. This shows the colors the hashes provide, while the hash-input being extended infinitely on the beat.





Convert ALL the things

If you need a (series of) encoding or hashes of a string, this is the right tool for the job. It provides an infinite number of conversions and an ever growing number of transformations.

Additionally it does not send anything to the server. It is written in client-side javascript.

This tool helps me a lot when playing CTF or when figuring out what a value means.





Made with WordPress

WordPress is the worlds most use content management system. With WordPress, i can focus on the content and know that the site just works.

WordPress has thousands of well maintained themes and plugins. I create and host websites on two multisite instances. 






Awesome Retro



Awesome Space



Hacker Hotel







Space Blogs







Hackerspaces NL



Elger Jonker



John Kr