@greyarea@mitra.vpclmulqdq.moe
Post #4033222
2026-07-22 21:54 UTC
@silverpill@mitra.social
No, the recipient would also generates an ephemeral key, and uses that when replying.
So it's always a one shot ephemeral (sender)/static (recipient) HPKE exchange, with sender authenticity guaranteed by the signature. Could also use the shared secret from the original post but force a different IV, but "replies are just the sender and receiver being flipped, code path is the same" is easier.
Replies (1)
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@silverpill@mitra.social 2026-07-23 10:22
@greyarea@mitra.vpclmulqdq.moe I assume this is "Authentication Using an Asymmetric Key" (https://www.rfc-editor.org/rfc/rfc9180.html#name-authentication-using-an-asy)? Because in "Encryption to a Public Key" mode, sender's key is not used. If I understand the idea correctly, the ephemeral key would need to be added to fep0806:cipherData. That is, instead of encap_key | ciphertext it will be ephemeral_key_pub | encap_key | ciphertext.