Trying to implement a mechanism for one way transmission of encrypted string values using ECC.
- Assume there is a fixed secret unavailable private key FPK, and public key FP for it is available to the application.
- As user enters a value, a new private key is generated, then shared key is produced from exchanging it from FP. Resulting sharing key is different every time.
- Symmetric encryption key DSK is derived from shared key using KDF (Scrypt or HKDF).
Possible option is to follow the ECDH hybrid scheme as described here
Is there any advantage of generating additional random symmetric key RK here to encrypt the value, then encrypt RK with DSK (and pay additional transmission overhead), or it is safe enough to just use DSK directly for symmetric encryption of the value?