During the competition there was at some point a Craiglist kind of paper for a synapse experiment with Neurosoft (The company that implements chips in your brain).

On the coupon was a website neuro://synapse-trials.ctf and a phone number 1-647-490-NSEC. After checking the website, we could find in the source page of the page this flag:


Next was the number, the NSEC correspond to 6732 (looking at an old phone keyboard). After calling the 1-647-490-NSEC number we get the what seemed to be NeuroSoft hotline.

They greet you and inform you that the waiting time is unusually long, before putting some music. After multiple your call is important to us and 2'30" of music we finally get to ear Cameron, which soon starts shooting binaries at us:

After using software phone, we can record the whole call, then thanks to our own Voice To Text implementation (we could have used a software available online) we manage to get the message:

Please verify that you are not fully human:
1000110100110010000011 000111010110110000111100001110 110011011001001101110010110011 011100001111100111000101100101

Now it’s time to decrypt the binary, it will surely be something in ascii starting like FLAG-. However when converting to 8-bits we get gibberish:

BIN (8bit)	2u7,>qe

However something is intriguing because the first bits almost looks like F (01000110 very much like 1000110). As if it was missing a 0 in front.

We got the answer a bit too late, after using dcode.fr, we manage to get the flag which was 7-bits encoded.

BIN (7bit)	FLAG-CallMeMaybe

Here is how 7 bit and 8 bit encoding looks like next to each other. The first 0 is just trimmed.

# 8 bit
01000110 01001100 01000001 01000111 00101101 01000011 01100001 01101100 01101100 01001101 01100101 01001101 01100001 01111001 01100010 01100101
# 7 bit
 1000110  1001100  1000001  1000111  0101101  1000011  1100001  1101100  1101100  1001101  1100101  1001101  1100001  1111001  1100010  1100101