CryptoHack
Break real cryptography with code and climb the scoreboard
CryptoHack is a set of puzzles about modern cryptography. Each challenge gives you a cipher, a server or some data, and you write code to break it and find the flag. Topics include symmetric ciphers, RSA, Diffie-Hellman, elliptic curves, hash functions, lattices and zero-knowledge proofs.
Free · No login · Browser · Intermediate
About CryptoHack
It trains the math and coding behind real crypto attacks. Short courses on modular arithmetic and other basics help you start, and the later challenges get very hard. Almost all challenges are written in Python 3, so Python makes things easier.
The platform is free and runs in the browser. You can play without an account, but you need to register to save your progress and appear on the scoreboard. It is funded by donations.
On Breakpoint since 23 Oct 2026.