Category Archives: Uncategorized

This year’s Google CTF was held over the weekend of the 22nd and 23rd of June, which for me was terrible timing. First it ended only one day before I was off to Glastonbury Festival, so I was a bit distracted by planning and packing for that. Then I also had a hospital appointment on the Saturday afternoon, which ate several hours of my time. But at least I did finally get to try one of these competitions live.

I set myself a target of getting into the top 100, which I didn’t achieve, but I was so close… I was only one stupid mistake away from solving the second problem that would have got me to my target. After the competition ended and I realised what I’d done I was able to finish solving it in less than an hour, but… too late!
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On Sunday I happened to notice that Google have taken down the challenges from their 2018 CTF competition, replacing the site with a notice about the imminent arrival of the 2019 one. This prompted me to revisit a couple of the challenges that I’d made progress on, but hadn’t completed, and with a little bit of cheating I’ve managed to finish them.
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I recently discovered the world of hacking CTF competitions. These competitions often contain a selection of individual challenges that exercise a whole range of skills related to hacking and computer security, but they all have one common goal… find the flag… which is usually just a recognisable, but hard to guess text string.

It all started after Youtube recommended a few videos from the LiveOverflow channel. That channel belongs to a German guy who’s created a large collection of short and easy to follow videos that give an excellent introduction to the subject. Then more recently I was watching another Youtube video where someone else was walking through the process of solving some of the challenges from the 2018 Google CTF competition. This video started by describing the Wired CSV challenge, where you’re given a photograph of a logic analyser connected to a chip and a CSV file containing the readings.

I immediately knew that i could solve this and had to stop the video before I got any spoilers. So I set aside a weekend and decided to see how much I could do in the same 48 hour period that I’d have had if I’d entered the real competition.
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This is my MQTT client library for Contiki.
It is completely asynchronous, starting a new process to handle communication with the message broker. It supports subscribing, publishing, authentication, will messages, keep alive pings and all three QoS levels. In short, it should be a fully functional client, though some areas haven’t been well tested yet.

See the example below for usage.
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