General Improvements

[daxpedda]

• Require Copy for both public and private key and switch to points instead of using PublicKey-like types.
• Require Zeroize for both public and private key instead of only using KeGroup::zeroize_sk_on_drop() on the private key.
• Fixed some missing checks in the ristretto255 implementation for zero scalars and identity elements during deserialization.
• Base the X25519 implementation on curve25519-dalek instead of x25519-dalek to support Zeroize and drop two dependencies.
• Use derive_where(ZeroizeOnDrop) instead of manual implementations.
• Update argon2 to v0.4.
• Remove unnecessary getrandom and constant_time_eq dependency.
• Update derive-where to v1.0.0-rc.3
• Remove unnecessary base64, lazy_static and sha2 dev-dependencies.
• No multiple versions of the same dependency present anymore 🎉 (clippy::multiple_crate_versions).
• Rename ristretto255_* and x25519_* crate features to ristretto255-* and x25519-*.
• Remove unnecessary dependency feature activation of rand/std, rand/std_rng and voprf/std.
• Fix possibility to produce zero scalars through KeGroup::hash_to_scalar (this is handled by the newest OPAQUE draft and the check added here should be removed).
• Rename CipherSuite::OprfGroup to CipherSuite::OprfCs.
• Rename TripleDH to TripleDh.
• Remove slow-hash crate feature, argon2 should be used instead.
• Rename SlowHash to Ksf (Key Stretching Function, as it is called in the spec).
• Remove custom De/Serialize implementation for most types 🎉 (this removes the macro and uses derive instead).

[kevinlewi]

Thanks! Is this still meant to be in draft mode?

[daxpedda]

I definitely plan to do more here, I'm continuing now actually. But I can also split it into multiple PR's or take it out of draft more, whatever you prefer.

[kevinlewi]

It would be nice to be able to sync the implementation with the latest draft and its changes (https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-opaque-08.html). I'd be happy to work on that, but want to avoid any potential merge conflicts, since I will be pulling from the main branch. If you think it would be better to land these changes now, let me know and I can merge before starting my work.