Crackd is a confidential 1v1 code-breaking game (think Mastermind) built on Zama’s fhEVM. You pick a secret 4-digit code; it’s sealed on-chain as an encrypted euint8[4], and every guess is scored directly on the ciphertext, so the code is never revealed to the opponent, the server, or the chain itself.
Play live: crackd-fhe[dot]vercel[dot]app
How it works: crackd-fhe[dot]vercel[dot]app/how-it-works
Code: github[dot]com/martinvibes/Crackd-Fhe
Demo video: youtu[dot]be/<7PpS6Z971tI>
Why it’s a real FHE use case
The hard part of Mastermind isn’t hiding the code, it’s scoring a guess without decrypting it, including the tricky duplicate-digit case. CrackdFHE computes both peg types entirely on ciphertext:
- POT (right digit, right place): per position,
FHE.eq(secret[i], guess[i])→ encrypted bool → summed. - PAN (right digit, wrong place): per digit value,
FHE.min(count_in_secret, count_in_guess)minus the POTs, so duplicates never over-count.
Ops used: FHE.fromExternal, FHE.eq, FHE.min, FHE.add, FHE.sub, FHE.select, FHE.allow. The encrypted feedback handles are ACL-granted to the guesser, who decrypts them client-side via the relayer’s userDecrypt.
No trusted referee, no commit-reveal that leaks at the end, no ZK circuit, the contract is the referee, because it computes on data it can’t read.
Two-sided & fully confidential
It’s a real duel: you seal your code, the AI “Vault” seals its, and you alternate turns cracking each other, with every score on-chain, on ciphertext. There’s also a “Decrypt my code” button that pulls your sealed code back from the chain and unseals it just for you- proof it lived encrypted the whole time.
Stack: @fhevm/solidity, @zama-fhe/relayer-sdk, Hardhat, React + Vite, Node/Express. Live on Ethereum Sepolia (frontend on Vercel, backend on Railway).
Deployed contract: CrackdFHE 0x9A050f34B461D984ca227874265Bc2969024257a
Would love feedback — happy to answer anything about the ciphertext scoring! 