Cryptopals
Write code that breaks real crypto, one set of challenges at a time
Cryptopals is a list of coding exercises where you build and then break real cryptography. You start with simple tasks like hex and base64 conversion and XOR ciphers, then move on to attacks on block cipher modes, random number generators, hashes and public key systems. The attacks come from weaknesses found in real-world systems.
Free · No login · Browser · Intermediate
About Cryptopals
There are eight sets, and each one is harder than the last. You do not need to know any crypto to start, but you should be able to code well. It suits programmers who want to understand how crypto fails in practice.
There is no account and no submission system. You read each challenge on the site and solve it on your own machine, in any language you like. It is free.
On Breakpoint since 23 Oct 2026.