Refactor: `noise-sv2` crate

[rrybarczyk]

Background

This task is an outcome of the protocols Rust docs issues tracked in #845.

While documenting protocols::v2::noise-sv2 in #1013, areas of potential code debt were identified. This issue servers as a place to list out these items to then be addressed in an organized manner. The initial Rust documentation effort was an immediate action, while a refactoring (which implies breaking API changes) is not so urgent priority, so for now we should leave this in the backlog for an appropriate moment in the future.

Identified Potential Code Debt

• Consider movingnoise_sv2::cipher_state::GenericCipher enum + associated logic to its own noise_sv2::generic_cipher module. Or, perhaps given the comment in the #916 discussion and the removal of AES256GCM in this sv2-spec PR, we do not need the GenericCipher at all? Do we plan so support anything other than ChaCha20Poly1305 in the future?
• Consider moving noise_sv2::cipher_state::Cipher struct and associated logic into its own noise_sv2::cipher module.
• unwraps in the impl From<[u8; 74]> for SignatureNoiseMessage from method.
• There is no custom Result type alias around our custom Error enum. Should add and use this everywhere we have a std::result::Result type.
• Consider making handshake::HandshakeOp trait public so users can call Responder::generate_key().

[Shourya742]

I noticed a few unwrap calls in the initiator, responder, and signature modules. It's generally not advisable to use unwrap in a library crate since it can cause the program to panic if an error occurs. Below are the locations where unwrap is being used:

• initiator.rs

  let plaintext: [u8; SIGNATURE_NOISE_MESSAGE_SIZE] = to_decrypt.try_into().unwrap();
  let signature_message: SignatureNoiseMessage = plaintext.into();
  let rs_pub_key = PublicKey::from_ellswift(elligatorswift_theirs_static)
      .x_only_public_key()
      .0
      .serialize();
  let rs_pk_xonly = XOnlyPublicKey::from_slice(&rs_pub_key).unwrap();

• responder.rs

  // 7. appends `EncryptAndHash(SIGNATURE_NOISE_MESSAGE)` to the buffer
  let valid_from = std::time::SystemTime::now()
      .duration_since(std::time::UNIX_EPOCH)
      .unwrap()
      .as_secs();

• signature_message.rs

  let now = SystemTime::now()
      .duration_since(SystemTime::UNIX_EPOCH)
      .unwrap()
      .as_secs() as u32;
  
  let version = u16::from_le_bytes(value[0..2].try_into().unwrap());
          let valid_from = u32::from_le_bytes(value[2..6].try_into().unwrap());
          let not_valid_after = u32::from_le_bytes(value[6..10].try_into().unwrap());
          let signature = value[10..74].try_into().unwrap();

We should propagate these errors instead of using unwrap and allow the implementing binary to handle them appropriately.

[Fi3]

they are inffalible, if you prefer you can use expect. I strongly suggest to not propagate error for impossible cases as we would only make the code harder to understand.

[Shourya742]

Based on the discussion about using the multi-cipher (referenced here: #916 (comment)), we need to remove AES_256_GCM from our codebase and update the specs accordingly.

[Shourya742]

Considering the comment by @plebhash here: #916 (comment), and the removal of aes_256_gcm, we will now use chacha20poly1305::Error instead of aes_gcm::Error. Although we could have used aead::Error, since we've finalized using only chacha20poly1305, it makes sense to use chacha20poly1305::Error now.

[rrybarczyk]

Considering the comment by @plebhash here: #916 (comment), and the removal of aes_256_gcm, we will now use chacha20poly1305::Error instead of aes_gcm::Error. Although we could have used aead::Error, since we've finalized using only chacha20poly1305, it makes sense to use chacha20poly1305::Error now.

Just so we know, the aes-gcm lib appears in the util/buffer/Cargo.toml as well and should be removed.

%rg aes_gcm -i -l

protocols/v2/noise-sv2/src/cipher_state.rs
protocols/v2/noise-sv2/src/aed_cipher.rs
protocols/v2/noise-sv2/src/responder.rs
protocols/v2/noise-sv2/src/handshake.rs
protocols/v2/noise-sv2/src/lib.rs
protocols/v2/noise-sv2/src/initiator.rs
protocols/v2/noise-sv2/src/error.rs
protocols/v2/noise-sv2/tmp.rs
utils/buffer/src/lib.rs
utils/buffer/src/buffer.rs
utils/buffer/src/buffer_pool/mod.rs

[Shourya742]

Based on the discussion about using the multi-cipher (referenced here: #916 (comment)), we need to remove AES_256_GCM from our codebase and update the specs accordingly.

The specs have been updated with this PR.

[plebhash]

potentially relevant here: stratum-mining/sv2-spec#65

[Shourya742]

Reminder: Add a unit test to the noise-sv2 module. See discussion: #1111 (comment)