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what would be the best way to encrypt a cast, so that only a set of selected fids can decrypt it?

(ofc not in warpcast, warpcast would only see gibberish)

Sounds like Broadcast Encryption
https://crypto.stanford.edu/~dabo/pubs/papers/broadcast.pdf

customer support @supercast

trying to sound smart /doingnumbers

Researcher at https://chainlight.io 🔗‍💥🔦,
Building https://relicprotocol.com

thanks! any good js or python implementations?

Hmm I'm not seeing any 😕. Btw, if the recipient sets are small, you could always just encrypt the message for each recipient and broadcast the ciphertexts. The benefit of the above system is that ciphertext size is independent of the # of recipients.

But, it requires a setup that generates keys for each user, which is impractical for a decentralized use case. It feels like you may be able to solve this with MPC, or directly with a new broadcast encryption scheme: https://eprint.iacr.org/2023/874.pdf

This takes you deep down the cryptography rabbit hole though 😅