(aka use the CipherSuite just like the others)
Repair the generics in KE trait: it makes sense that generate_ke[1-3] should operate on the same key representation.
We used to have three problems:
- overuse of the <Sha256 as Digest>::OutputSize, which is just, well, U32. Sometimes used as a parameter (as in generate_oprf1), sometimes as a constant (as in generate_oprf3).
- the `hash_to_curve` operation for `RistrettoPoint` which requires 64 bits of input entropy, is fed 64 bits of which the last 32 are zero,
- the `hash_to_curve` operation for `Curve25519Point` which requires 32 bits of input entropy, is fed 64 bits of which the last 32 are discarded,
This corrects all three and uses U32 where the size of the digest is not meant to be a constraint.
Addresses #15 partially.
François Garillot