EIP-5630: Encryption and Decryption

[firnprotocol]

hello @ronaldmannak, apologies, I missed your message when you first posted it. thanks for your contribution and glad to have you on board.

@ronaldmannak

Have you considered using the GPG model where the message itself is encrypted with a one-time symmetrical session key, and the session key itself is encrypted with the recipient’s public key? This would scale for multiple recipients.

actually, this is an almost exact description of how ECIES works, and is actually the only way to use asymmetric encryption for long messages. indeed, “true” asymmetric encryption only works for short messages—say, on the order of 32 bytes. everything longer than that, you’ll use the “hybrid” style of encryption you described above, which is what both GPG and ECIES use.

@ronaldmannak

I’d suggest to use proven models, unless there is a good reason not to (there might be one that I missed, feel free to correct me).

the model we propose is proven (and in fact this is true regardless of whether you use the HKDF to go from signing key ⟶ decryption key or not). the only model which is not proven secure is that of EIP-1024, in which the same secret key is used for both signing on the secp curve and simultaneously for decryption on curve25519.