Resources

Here are some useful resources for getting started with CTF problems:

https://trailofbits.github.io/ctf/

A complete course on several CTF challenge categories.

http://overthewire.org/wargames/

Practical exercises with good difficulty progression.

https://cryptopals.com/

Cryptography challenges.

http://smashthestack.org/

Binary exploitation challenges.

https://ctftime.org/

Check here for upcoming CTFs - nothing like the real thing to learn quickly!