User Addresses are hashes of Public Keys

[huitseeker]

This advances #318.

Main changes:

• cryptographic operations are moves from base_types to a separate crypto file.
• the behavior of the Authorities' signatures does not change,
  • their signatures are a new type AuthoritySignature, which is just an alias of the former Signature type.
  • Signing, signature verification, do not change for Authorities.
  • We remove references to their address where relevant, i.e. in the separation of SuiAddress (hashes of user PublicKeys) and PublicKey, authorities only manipulate and concern themselves with the later.
• the Signature type is introduced:
  • it consists of the bytes of an ed25519 signature, followed by the bytes of the public key this signature is valid for,
  • it's straightforward to tweak an implementation of a Signer producing a certain type of signature into one that appends the bytes of the public key after the signature, for all reasonable signers,
  • we demonstrate this by augmenting the existing impl signer::Signer<AuthoritySignature> for our KeyPair type with an impl signer::Signer<Signature>,
  • the verification (check) of this new user Signature type now takes a SuiAddress argument
  • on top of verifying the validity of the cryptographic signature for its embedded public key, check also checks the PublicKey indeed hashes to the expected SuiAddress passed as an argument.
• the SuiAddress type is a 32-byte array
  • it's produced by hashing a PublicKey using SHA3-256 into a 32-byte array,

Possible Follow-ups

• debate and decide on a faster hash function with a smaller output size (20 bytes comes to mind)
• debate and decide on renaming Signature to UserSignature
• split get_key_pair into random_user_keypair which returns (SuiAddress, KeyPair), and random_authority_keypair which returns (PublicKeyBytes, KeyPair),
• ... and make sure those are only called in tests.

Ancillary changes

• we tweak the hex encode / decode functions introduced in Generalize hex encode and decode functions #466 to operate on a bound of for <'a> TryFrom<&'a [u8]> rather than Vec<u8>

[lxfind]

Nice!

[lxfind]

What's this change for?

[huitseeker]

This filtered the target branches that would trigger a CI run on a PR.

[huitseeker]

Opened #481 for leftovers