This is really just an intro challenge. Download the flag file and open it in a text editor. The file contains the clear text flag. Dead simple.
Flag
picoCTF{s4n1ty_v3r1f13d_4a2b35fd}
More interesting than the challenge itself is the question “What are the setters trying to achieve with this challenge?” A couple of things spring to mind immediately.
Firstly, this challenge acts as an orientation to CTFs in general and to the picoCTF site in particular. If you’ve never done a CTF before then it’s helpful to just get familiar with the mechanics of the process before trying to tackle any technical material. So all this challenge is doing is presenting some instructions to follow, encouraging the user to follow those instructions, achieve the desired result and confirm that they have done so – the four stages in any CTF. Other than being able to open a file there is no technical challenge involved; no material to learn, no research to do.
Which kind of points up the second purpose of this challenge. I can envisage some users who will download a file called flag, double click on it in their OS and not have it appear in a text editor – I’m thinking a typical Windows user for example, who might never have come across a file without an extension. So I guess there is, for that type of user at least, an element of technical challenge. A hint of the discomfort to come perhaps?
So, seems like a pretty well designed challenge to me, in that it achieves very well what it sets out to achieve.