Add RNG and generate ephemeral keys

[geonnave]

Addressing #41 and #42.

This PR adds support for generation of ephemeral private keys, as well as derivation of public keys. It also updates prepare_message_1 and prepare_message_2 to accept an ephemeral keypair as parameter.

The implementation differs for each crypto backend:

• hacspec: relies on the rand crate
• psa: uses psa_crypto::operations::key_management::generate
• cryptocell310: uses CRYS_ECPKI_GenKeyPair
• cc2538: just a mock for now

[geonnave]

Yes, it is because of the different types.

[malishav]

Before invoking the hacspec function, why don't you convert the array to ByteSeq like in https://github.com/openwsn-berkeley/edhoc-rs/blob/main/crypto/edhoc-crypto-hacspec/src/lib.rs#L50? This would avoid code duplication from hacspec

[geonnave]

You are right, fixed.

[malishav]

Since this is now implemented, could you remove the G_X, X, G_Y, Y constants from consts/src/lib.rs for both modules?

[geonnave]

Since this is now implemented, could you remove the G_X, X, G_Y, Y constants from consts/src/lib.rs for both modules?

I can remove Y and G_Y, as I am still using X and G_X for tests.

[malishav]

But why don't you move X and G_X then as test vectors in the test module? They should definitely not appear any more in consts.

[geonnave]

But why don't you move X and G_X then as test vectors in the test module? They should definitely not appear any more in consts.

Sounds good, will do it.

[malishav]

Congrats on getting this ready for merge! Merging now!