Every year publishes a challenge to reverse engineer and exploit something. Past challenges involved disarming simulation of IED (improvised explosive device), making sense of encrypted SSL traffic and so on.
This year the challenge was to analyze blockchain based ransomware, retrieve the decryption keys without paying and ultimately refund all the victims who already paid.
This year is the first time I managed to solve the entire thing with the other 19 finalists. Only 1.3% of the participants solved all 7 problems.
Use the links below for the complete walkthrough of each task