ASIS-CTF Finals 2014 - How Much Exactly? (25pts) writeup

The challenge description was: 4046925: How much the exact IM per year? flag = ASIS_md5(size)

So it doesn't say much, after googling the description we find an interesting PDF file on nsa.gov title Untangling The Web.

https://www.nsa.gov/public_info/_files/untangling_the_web.pdf

After skimming through the big (34MB) document we can understand that we have to narrow our search to even be sure we are on the right track. Looking for year yelds 134 results, it could take a while to go through each result and be sure it's what we are looking for. IM could mean anything, let's search for Instant Messaging and see how many results we got: 10. Much better. First result is the following:

Search Fundamentals
...
Instant messaging generates five billion messages a day (750GB), or 274 Terabytes a year.

Let's try the size of Terabytes per year it could be our flag:

mrt:~/asis/caplow$ echo -n "274" | md5sum -
d947bf06a885db0d477d707121934ff8  -

Challenge accepted our answer.

We got our flag:

ASIS_d947bf06a885db0d477d707121934ff8