If two parties calculate an ECDH shared secret can they (with no security weakness) use this raw value directly as an encryption key, assuming the underlying key and ECDH sizes match?
Also the situation I'm specifically looking at using static ECC keys, not ephemeral ones, but I would also be curious if using the raw ECDH value for encryption may be OK when using ephemeral keys. I do understand that it is ~trivial to apply a KDF to the ECDH secret but I am evaluating an existing system. The system uses
p256r1 and is using the resulting x-coordinate as the shared secret.