New API Proposal: Add (expose) ECC methods

[Sajjon]

NEW API Proposal: Add (expose) ECC methods

Motiviation

We should expose some Elliptic Curve Cryptography (ECC) methods, at least:

1. Point multiplication
2. Decode point on curve from a compressed public key.

So that developers can develop cryptographic constructs using these fundamental building blocks. e.g. ECIES (here is my implementation)

An (EC) crypto lib which does not expose at least these above-mentioned methods is extremely limiting.

Alternate solution

Alternatively, we can include common cryptographic constructs such as above mentioned ECIES in this library - but it is more limiting and sounds like lots of work - and more maintenance....

Importance

If above mentioned cryptographic primitives - especially EC point multiplication - are not expose then crypto companies and cryptocurrency project might have to turn to other solutions. Which would be sad really, since this repo could improve the whole crypto sphere (on the Swift side of things).

[Lukasa]

Thanks for this proposal!

I think at this time this proposal is explicitly out of scope. The goal of this library is to provide safe, high-level constructions; we are not trying to expose primitives for composition. I appreciate that this is limiting, but we want to avoid the kitchen-sink style API design of lower-level libraries.

I think there is absolutely value in high-quality libraries exposing primitives for Swift users interested in implementing novel or unusual cryptographic constructions, but that belongs elsewhere.

Thanks for the proposal though, please keep them coming!

[FredericJacobs]

Hey @Sajjon,

Thanks for the proposal!

I just want to point out that in order to perform ECIES, everything is already there.
The only operation you need to perform over elliptic curves is a DH key agreement which we expose on the EC private key types.

See this example for P256: https://developer.apple.com/documentation/cryptokit/p256/keyagreement/privatekey/3243096-sharedsecretfromkeyagreement

[Sajjon]

@FredericJacobs @Lukasa Thanks for pointing that out Frederic! So how do you feel about including an implementation of ECIES - if I were to do a (draft) PR with an initial implementation?

[FredericJacobs]

Primitives used in ECIES will vary from protocol to protocol. We are currently not taking any PRs for higher-level constructions that can be built on top of Swift Crypto. If you are interested, we have an ECIES variant in the Swift playground that was released at WWDC.

[Sajjon]

@FredericJacobs Got it, makes sense.

Thanks for that playground, I have not seen it before. Now that I've looked at it, it contains some typos, multiple instances of:
"ephmeral" -> "ephemeral"

Very nice playground! I must start using playgrounds more, it's kind of similar to Juniper "books" in Python.