bittorrent
Beta
A BitTorrent client
Bencode, trackers and the peer-to-peer protocol. Download a real file by talking to real peers.
Advanced12 stages~20 hNetworking
bencodep2pprotocolos+1
Go · Python · Java
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Project hash-functionsSecurityIntermediateBeta
SHA-256 and HMAC from scratch
Rotations, padding and the compression block. Sign and verify messages without touching a crypto library.
Build it in your language
The tester treats your program as a black box: any language works. These are just the most convenient ones for this project.
What this project is about
A cryptographic hash is a function that shows up everywhere — passwords, signatures, blockchains, file integrity — and that almost nobody has seen from the inside. Inside, it's rotations and additions, nothing more.
You'll implement SHA-256 from the padding to the compression block, check your output against the official test vectors, and use it to build HMAC and sign real tokens.
Roadmap
7 stages across 3 phases. Every stage comes with its guide and its tests: you move on when they pass.
- Phase 12 stages
Preparing the message
Padding, length in bits, and splitting into 512-bit blocks.
- Phase 23 stages
The heart of the hash
Message schedule, the 64 rounds, and validation against the NIST vectors.
- Phase 32 stages
Putting it to use
HMAC-SHA256, and signing and verifying tokens in constant time.
Before you start
A standards-conformant SHA-256 implementation (padding, message schedule and the 64 compression rounds), validated against the NIST vectors, plus HMAC-SHA256 on top and a utility that signs and verifies tokens with constant-time comparison.