Specifications
| Format | Challenges |
|---|---|
| Level | Beginner, Intermediate, Advanced |
| Price | Free |
| Access | No registration |
| Activity | Active |
| Language | EN |
| Category | Cryptography |
Cryptography tasks from classical ciphers to protocol-level bugs, grouped into topic pyramids, each with an interactive hint mode. Counting the per-topic counters gives about 316 challenges, some of them from the community CTF archive rather than the platform.
Pros & cons
Pros
- Topic pyramids take you from XOR to block ciphers in order
- Hint mode explains the primitive when you get stuck
- Free, no account, no schedule
Cons
- Crypto only: no web, reversing, forensics or infrastructure to practise
- Some challenges turn on English wordplay, which is a language barrier, not a crypto one
- The larger challenges assume you can read code and reason about a protocol
Who it fits
Fits the gap most CTF crypto fails in: not a missing vulnerability but no understanding of the primitive underneath. Useful as a bridge between a textbook and a real challenge.
Getting started
- Work through the general and XOR basics without skipping the writeups
- Code every step instead of solving it in your head, even the early ciphers
- Keep a reference implementation of the primitive open and compare line by line
History
Built to explain crypto rather than hand out puzzles, and it has kept that shape. Free throughout, with the challenge set growing in bursts when new categories appear. The task count is a sum of per-topic counters, not a number the site publishes.
