Additional parameters to use in DEM?

[fjarri]

Our implementation of DEM takes additional parameters in several places:

• HKDF (kdf()) takes salt and info
• AEAD (DEM) takes aad (additional authenticated data)

We use DEM in two places:

• to encrypt SecretKey during serialization. We set info there to a predefined tag.
• to encrypt the plaintext in encrypt() (being added in Interfacing with Python #41). We use the serialized Capsule as aad.

Do we need to use other parameters too in these cases? @cygnusv , @tuxxy

[cygnusv]

Do we need to use other parameters too in these cases?

No, I don't think it's necessary, particularly the salt parameter is not useful for us (we never start with low-entropy input).
I guess you're asking this because of this line?

rust-umbral/umbral-pre/src/dem.rs

Line 33 in 128eb0c

let key_bytes = kdf(&key_seed, None, None);

I think that's fine.

BTW, a side note:

to encrypt SecretKey during serialization

I think we can/should remove this from Umbral anyway (@tuxxy wdyt?)

[fjarri]

Ok, so no HKDF info for encrypt() either?

I think we can/should remove this from Umbral anyway

It is currently removed (it was in at some point, but I did remove it after our discussion)

[cygnusv]

Ok, so no HKDF info for encrypt() either?
Yeah, no need.

[fjarri]

Great, I guess I can close it then. TODOs to be removed along with other RFCs in #41