lucasg.github.io blog about rss github

HACKVent 2014 - Day 05 writeup

I’ve sign up for the Hackvent event made by the guys from www.hacking-lab.com, which is a advent-like hacking competition. Every day there is a new challenge posted at midnight which has a to solved at best in the same day, the challenge becoming increasingly more difficult every week completed. The aim in every puzzle is to find either a qr-encoded x-mas ball with lead to the validation code, or a secret human-readable string which gives you the former ball when feeding into a validator (the “Ball-O-Matic”).

Here’s the write-up for the fifth challenge, in which we will compare apples and oranges.


For the Day 05 Hackvent challenge, we were given the following instructions :

Riddle from hackvent.hacking-lab.com for Day 05

I’m not an English native person, so I don’t know half of the idiomatic expressions used here like “baker’s dozen” or “donkeypower”. Like any other human being, I google’d them. To my surprise, Google directly returns the numerical value in the calculator :

Bakers like to brag

Results from google calc :

  • megasecond : 10e6 s
  • baker dozen : 13
  • donkeypower : 250.033167 W
  • number of horns on a unicorn : 1
  • once in a blue moon : 1.16699016 10e-8 Hz
  • answer to life the universe and everything : 42
  • a beard second : 5 nm
  • earth mass : 5.97219 10e24 kg

Once I got all this number, I didn’t feel like I was getting progress. I got a hint previously from the author of the challenge saying that the result is a integer and all I got was floating-point values due to earth mass and once in a blue moon being floats. Moreover, dimensionnal analysis wasn’t concluant : I think the resulting unit is in N.s-2*, which mean nothing to me.

The breakthrough came when I directly typed the following phrase into google :

A rubbish computation

Google translated a floating operation into a integer ! From then on, I knew I just had to punch the whole equation into Gooogle’s search bar. You can use brackets “[ ]” to encapsulate sub-operations :

 [number of horns on a unicorn once in a blue moon]/[answer to life the universe and everything][bakers dozen donkeypower]/[a beard second squared earth mass]*[(half a megasecond) squared squared]

a completely non-sensical result