I am using a PQ-KEM to get a 32 byte shared secret. I want to derive 2 keys , 1 for encryption of message using AES-CTR and another for HMAC-512. can I safely ignore salt and info parameter in hkdf-sha512 as they are marked optional?
I want to skip salt parameter because in https://datatracker.ietf.org/doc/html/rfc5869#section-3.4 it is given attacker must not manipulate salt parameter. in my application salt for hkdf , info parameter will be sent along with encrypted message with HMAC, however in recipient side before verification of HMAC , the salt and info values sent along with encrypted message has to be used to derive keys using hkdf to derive key to verify HMAC , only then i could authenticate salt , info and ciphertext. I guess this will make my crypto insecure am I correct?