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HACKvent 2015: Day 6

08 Dec 2015
CTF: Hackvent 2015
Link to challenge: http://hackvent.hacking-lab.com
Date Completed: 08 December 2015

Challenge

We are given the following string:

Solution

We can deduce by the amount of padding that this is Base32 encoded string. We use an online decoder and get:

Then we try various other things to decode the above string. I will admit I failed to find a proper solution until I received some help from SlEePlEs5 on the hacking-lab IRC. Then I was able to realise that I had to decode the above string using ASCII85. I get:

Great! This looks a lot like our nugget. I guess a simple Caesar cipher is required here and find the offset number to be 13 (as we want U->H for first character in our nugget). We apply the cipher (basically ROT13) and get our flag!

Flag:  HV15-t9P8-QaIV-J0Ar-83F3-M8Dc

 
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