Capture the Flags (CTFs) are competitions that involve many aspects of information security: cryptography, steganography, binary analysis, reverse engineering, mobile security and others.
There are two common types of CTFs: Jeopardy and Attack-Defence.

PoliCTF is a Jeopardy style CTF.
It has some questions (challenges) of different categories (Crypto, Reversing, Web, Pwnable, Forensics, GrabBag).
The objective of each challenge is to recover a special string called flag. PoliCTF flags are in the format "flag{}". The whole string including "flag{" and "}"" needs to be submitted as flag.
Teams gain points for every solved challenge.
The first three solvers for a challenge get bonus points (6%, 4% and 2% of the challenge value).
Some challenges are initially locked and can be opened only after some team solve unlocked challenges.

PoliCTF scoreboard can be accessed here.
You can download the packages of challenges directly from the scoreboard, or from this torrent. (Some challenge will be available only on the torrent)
Each package has been encrypted with AES-256.
You can find the decryption keys on the scoreboard below the description of each challenge (if the challenge is open).
To decrypt the packages you can use GPG:
gpg -o <output_file> -d <encrypted_file>
(Type the correct key when requested)