Well this was one of the more interesting flags this year at the DefCon CTF Qualifiers. It was a throw back to pretty cool old school decryption.
Here is what I did to solve it:
1. They give you a single text file and no URL to poke at.2. The content of the text file was as follows:
> Anyo!e!howouldsacrificepo!icyforexecu!!onspeedthink!securityisacomm!ditytop!urintoasy!tem!
Looking at this it is hard at first to make much of a connection out of the data.
3. First I considered the possibility that it required you to shift letters or choose letters in a patterned fashion like every other letter.4. Looking at all of this I wasnt able to make much sense or see a pattern that fit.5. However it dawned on me that if we counted the letters between the ! marks that maybe I could try it as traditional alaphbet cipher.6. The values that you get when you try this method is as follows:
41181101215793
7. At first I tried what is a more traditional alphabet cipher which is as follows:
A=0B=1C=3
and so on.
8. However when I tried this I found that it resulted in an answer that made no sense.9. I thought back to the clue and they mentioned that the flag was in a non-standard form and multiple word seperated with a space.10. Seeing that it had atleast one space in it I noticed the 0 was in the middle of the number string and tried shifting the letters over to allow 0 to equal a space.11. When I did that I got the following:
DARK 
LOGIC
12. And with that I found the flag:
dark logic
