serai/coordinator/src/tributary/handle.rs

use core::{ops::Deref, future::Future};
use std::collections::HashMap;

use zeroize::{Zeroize, Zeroizing};

use ciphersuite::{group::GroupEncoding, Ciphersuite, Ristretto};
use frost::dkg::Participant;

use scale::{Encode, Decode};
use serai_client::{
  Public, Signature,
  validator_sets::primitives::{ValidatorSet, KeyPair},
  subxt::utils::Encoded,
  SeraiValidatorSets,
};

use tributary::{Signed, TransactionKind, TransactionTrait};

use processor_messages::{
  key_gen::{self, KeyGenId},
  coordinator::{self, SubstrateSignableId, SubstrateSignId},
  sign::{self, SignId},
};

use serai_db::{Get, Db};

use crate::{
  processors::Processors,
  tributary::{
    Transaction, TributarySpec, SeraiBlockNumber, Topic, DataSpecification, DataSet, Accumulation,
    nonce_decider::NonceDecider,
    dkg_confirmer::DkgConfirmer,
    scanner::{RecognizedIdType, RIDTrait},
    FatallySlashed, ShareBlame, PlanIds, ConfirmationNonces, KeyPairDb, AttemptDb, DataDb,
  },
};

use super::CurrentlyCompletingKeyPair;

const DKG_COMMITMENTS: &str = "commitments";
const DKG_SHARES: &str = "shares";
const DKG_CONFIRMATION_NONCES: &str = "confirmation_nonces";
const DKG_CONFIRMATION_SHARES: &str = "confirmation_shares";

// These s/b prefixes between Batch and Sign should be unnecessary, as Batch/Share entries
// themselves should already be domain separated
const BATCH_PREPROCESS: &str = "b_preprocess";
const BATCH_SHARE: &str = "b_share";

const SIGN_PREPROCESS: &str = "s_preprocess";
const SIGN_SHARE: &str = "s_share";

pub fn dkg_confirmation_nonces(
  key: &Zeroizing<<Ristretto as Ciphersuite>::F>,
  spec: &TributarySpec,
  attempt: u32,
) -> [u8; 64] {
  DkgConfirmer::preprocess(spec, key, attempt)
}

// If there's an error generating a key pair, return any errors which would've occured when
// executing the DkgConfirmer in order to stay in sync with those who did.
//
// The caller must ensure only error_generating_key_pair or generated_key_pair is called for a
// given attempt.
pub fn error_generating_key_pair<G: Get>(
  getter: &G,
  key: &Zeroizing<<Ristretto as Ciphersuite>::F>,
  spec: &TributarySpec,
  attempt: u32,
) -> Option<Participant> {
  let preprocesses = ConfirmationNonces::get(getter, spec.genesis(), attempt).unwrap();

  // Sign a key pair which can't be valid
  // (0xff used as 0 would be the Ristretto identity point, 0-length for the network key)
  let key_pair = (Public([0xff; 32]), vec![0xffu8; 0].try_into().unwrap());
  match DkgConfirmer::share(spec, key, attempt, preprocesses, &key_pair) {
    Ok(mut share) => {
      // Zeroize the share to ensure it's not accessed
      share.zeroize();
      None
    }
    Err(p) => Some(p),
  }
}

pub fn generated_key_pair<D: Db>(
  txn: &mut D::Transaction<'_>,
  key: &Zeroizing<<Ristretto as Ciphersuite>::F>,
  spec: &TributarySpec,
  key_pair: &KeyPair,
  attempt: u32,
) -> Result<[u8; 32], Participant> {
  CurrentlyCompletingKeyPair::set(txn, spec.genesis(), key_pair);
  let preprocesses = ConfirmationNonces::get(txn, spec.genesis(), attempt).unwrap();
  DkgConfirmer::share(spec, key, attempt, preprocesses, key_pair)
}

pub(super) fn fatal_slash<D: Db>(
  txn: &mut D::Transaction<'_>,
  genesis: [u8; 32],
  account: [u8; 32],
  reason: &str,
) {
  log::warn!("fatally slashing {}. reason: {}", hex::encode(account), reason);
  FatallySlashed::set_fatally_slashed(txn, genesis, account);
  // TODO: disconnect the node from network/ban from further participation in all Tributaries

  // TODO: If during DKG, trigger a re-attempt
}

// TODO: Once Substrate confirms a key, we need to rotate our validator set OR form a second
// Tributary post-DKG
// https://github.com/serai-dex/serai/issues/426

fn fatal_slash_with_participant_index<D: Db>(
  spec: &TributarySpec,
  txn: &mut <D as Db>::Transaction<'_>,
  i: Participant,
  reason: &str,
) {
  // Resolve from Participant to <Ristretto as Ciphersuite>::G
  let i = u16::from(i);
  let mut validator = None;
  for (potential, _) in spec.validators() {
    let v_i = spec.i(potential).unwrap();
    if (u16::from(v_i.start) <= i) && (i < u16::from(v_i.end)) {
      validator = Some(potential);
      break;
    }
  }
  let validator = validator.unwrap();

  fatal_slash::<D>(txn, spec.genesis(), validator.to_bytes(), reason);
}

pub(crate) async fn handle_application_tx<
  D: Db,
  Pro: Processors,
  FPst: Future<Output = ()>,
  PST: Clone + Fn(ValidatorSet, Encoded) -> FPst,
  FRid: Future<Output = ()>,
  RID: RIDTrait<FRid>,
>(
  tx: Transaction,
  spec: &TributarySpec,
  processors: &Pro,
  publish_serai_tx: PST,
  key: &Zeroizing<<Ristretto as Ciphersuite>::F>,
  recognized_id: RID,
  txn: &mut <D as Db>::Transaction<'_>,
) {
  let genesis = spec.genesis();

  // Don't handle transactions from fatally slashed participants
  // TODO: Because fatally slashed participants can still publish onto the blockchain, they have
  // a notable DoS ability
  if let TransactionKind::Signed(signed) = tx.kind() {
    if FatallySlashed::get(txn, genesis, signed.signer.to_bytes()).is_some() {
      return;
    }
  }

  let handle = |txn: &mut <D as Db>::Transaction<'_>,
                data_spec: &DataSpecification,
                bytes: Vec<u8>,
                signed: &Signed| {
    let Some(curr_attempt) = AttemptDb::attempt(txn, genesis, data_spec.topic) else {
      // Premature publication of a valid ID/publication of an invalid ID
      fatal_slash::<D>(
        txn,
        genesis,
        signed.signer.to_bytes(),
        "published data for ID without an attempt",
      );
      return Accumulation::NotReady;
    };

    // If they've already published a TX for this attempt, slash
    if DataDb::get(txn, genesis, &data_spec.as_key(genesis), &signed.signer.to_bytes()).is_some() {
      fatal_slash::<D>(txn, genesis, signed.signer.to_bytes(), "published data multiple times");
      return Accumulation::NotReady;
    }

    // If the attempt is lesser than the blockchain's, slash
    if data_spec.attempt < curr_attempt {
      // TODO: Slash for being late
      return Accumulation::NotReady;
    }
    // If the attempt is greater, this is a premature publication, full slash
    if data_spec.attempt > curr_attempt {
      fatal_slash::<D>(
        txn,
        genesis,
        signed.signer.to_bytes(),
        "published data with an attempt which hasn't started",
      );
      return Accumulation::NotReady;
    }

    // TODO: We can also full slash if shares before all commitments, or share before the
    // necessary preprocesses

    // TODO: If this is shares, we need to check they are part of the selected signing set

    // Accumulate this data
    DataDb::accumulate(txn, key, spec, data_spec, signed.signer, &bytes)
  };

  fn check_sign_data_len<D: Db>(
    txn: &mut D::Transaction<'_>,
    spec: &TributarySpec,
    signer: <Ristretto as Ciphersuite>::G,
    len: usize,
  ) -> Result<(), ()> {
    let signer_i = spec.i(signer).unwrap();
    if len != usize::from(u16::from(signer_i.end) - u16::from(signer_i.start)) {
      fatal_slash::<D>(
        txn,
        spec.genesis(),
        signer.to_bytes(),
        "signer published a distinct amount of sign data than they had shares",
      );
      Err(())?;
    }
    Ok(())
  }

  fn unflatten(spec: &TributarySpec, data: &mut HashMap<Participant, Vec<u8>>) {
    for (validator, _) in spec.validators() {
      let range = spec.i(validator).unwrap();
      let Some(all_segments) = data.remove(&range.start) else {
        continue;
      };
      let mut data_vec = Vec::<_>::decode(&mut all_segments.as_slice()).unwrap();
      for i in u16::from(range.start) .. u16::from(range.end) {
        let i = Participant::new(i).unwrap();
        data.insert(i, data_vec.remove(0));
      }
    }
  }

  match tx {
    Transaction::RemoveParticipant(i) => {
      fatal_slash_with_participant_index::<D>(spec, txn, i, "RemoveParticipant Provided TX")
    }
    Transaction::DkgCommitments(attempt, commitments, signed) => {
      let Ok(_) = check_sign_data_len::<D>(txn, spec, signed.signer, commitments.len()) else {
        return;
      };
      match handle(
        txn,
        &DataSpecification { topic: Topic::Dkg, label: DKG_COMMITMENTS, attempt },
        commitments.encode(),
        &signed,
      ) {
        Accumulation::Ready(DataSet::Participating(mut commitments)) => {
          log::info!("got all DkgCommitments for {}", hex::encode(genesis));
          unflatten(spec, &mut commitments);
          processors
            .send(
              spec.set().network,
              key_gen::CoordinatorMessage::Commitments {
                id: KeyGenId { set: spec.set(), attempt },
                commitments,
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {
          panic!("wasn't a participant in DKG commitments")
        }
        Accumulation::NotReady => {}
      }
    }

    Transaction::DkgShares { attempt, mut shares, confirmation_nonces, signed } => {
      let sender_i = spec
        .i(signed.signer)
        .expect("transaction added to tributary by signer who isn't a participant");
      let sender_is_len = u16::from(sender_i.end) - u16::from(sender_i.start);

      if shares.len() != usize::from(sender_is_len) {
        fatal_slash::<D>(
          txn,
          genesis,
          signed.signer.to_bytes(),
          "invalid amount of DKG shares by key shares",
        );
        return;
      }
      for shares in &shares {
        if shares.len() != (usize::from(spec.n() - sender_is_len)) {
          fatal_slash::<D>(txn, genesis, signed.signer.to_bytes(), "invalid amount of DKG shares");
          return;
        }
      }

      // Save each share as needed for blame
      {
        let from_range = spec.i(signed.signer).unwrap();
        for (from_offset, shares) in shares.iter().enumerate() {
          let from =
            Participant::new(u16::from(from_range.start) + u16::try_from(from_offset).unwrap())
              .unwrap();

          for (to_offset, share) in shares.iter().enumerate() {
            // 0-indexed (the enumeration) to 1-indexed (Participant)
            let mut to = u16::try_from(to_offset).unwrap() + 1;
            // Adjust for the omission of the sender's own shares
            if to >= u16::from(from_range.start) {
              to += u16::from(from_range.end) - u16::from(from_range.start);
            }
            let to = Participant::new(to).unwrap();

            ShareBlame::set(txn, genesis, from.into(), to.into(), &share);
          }
        }
      }

      // Filter down to only our share's bytes for handle
      let our_i = spec
        .i(Ristretto::generator() * key.deref())
        .expect("in a tributary we're not a validator for");

      let our_shares = if sender_i == our_i {
        vec![]
      } else {
        // 1-indexed to 0-indexed
        let mut our_i_pos = u16::from(our_i.start) - 1;
        // Handle the omission of the sender's own data
        if u16::from(our_i.start) > u16::from(sender_i.start) {
          our_i_pos -= sender_is_len;
        }
        let our_i_pos = usize::from(our_i_pos);
        shares
          .iter_mut()
          .map(|shares| {
            shares
              .drain(
                our_i_pos ..
                  (our_i_pos + usize::from(u16::from(our_i.end) - u16::from(our_i.start))),
              )
              .collect::<Vec<_>>()
          })
          .collect()
      };
      // Drop shares as it's been mutated into invalidity
      drop(shares);

      let confirmation_nonces = handle(
        txn,
        &DataSpecification { topic: Topic::Dkg, label: DKG_CONFIRMATION_NONCES, attempt },
        confirmation_nonces.to_vec(),
        &signed,
      );
      match handle(
        txn,
        &DataSpecification { topic: Topic::Dkg, label: DKG_SHARES, attempt },
        our_shares.encode(),
        &signed,
      ) {
        Accumulation::Ready(DataSet::Participating(shares)) => {
          log::info!("got all DkgShares for {}", hex::encode(genesis));

          let Accumulation::Ready(DataSet::Participating(confirmation_nonces)) =
            confirmation_nonces
          else {
            panic!("got all DKG shares yet confirmation nonces aren't Ready(Participating(_))");
          };
          ConfirmationNonces::set(txn, genesis, attempt, &confirmation_nonces);

          // shares is a HashMap<Participant, Vec<Vec<Vec<u8>>>>, with the values representing:
          // - Each of the sender's shares
          // - Each of the our shares
          // - Each share
          // We need a Vec<HashMap<Participant, Vec<u8>>>, with the outer being each of ours
          let mut expanded_shares = vec![];
          for (sender_start_i, shares) in shares {
            let shares: Vec<Vec<Vec<u8>>> = Vec::<_>::decode(&mut shares.as_slice()).unwrap();
            for (sender_i_offset, our_shares) in shares.into_iter().enumerate() {
              for (our_share_i, our_share) in our_shares.into_iter().enumerate() {
                if expanded_shares.len() <= our_share_i {
                  expanded_shares.push(HashMap::new());
                }
                expanded_shares[our_share_i].insert(
                  Participant::new(
                    u16::from(sender_start_i) + u16::try_from(sender_i_offset).unwrap(),
                  )
                  .unwrap(),
                  our_share,
                );
              }
            }
          }

          processors
            .send(
              spec.set().network,
              key_gen::CoordinatorMessage::Shares {
                id: KeyGenId { set: spec.set(), attempt },
                shares: expanded_shares,
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {
          panic!("wasn't a participant in DKG shares")
        }
        Accumulation::NotReady => assert!(matches!(confirmation_nonces, Accumulation::NotReady)),
      }
    }

    // TODO: Only accept one of either InvalidDkgShare/DkgConfirmed per signer
    // TODO: Ban self-accusals
    Transaction::InvalidDkgShare { attempt, accuser, faulty, blame, signed } => {
      let range = spec.i(signed.signer).unwrap();
      if (u16::from(accuser) < u16::from(range.start)) ||
        (u16::from(range.end) <= u16::from(accuser))
      {
        fatal_slash::<D>(
          txn,
          genesis,
          signed.signer.to_bytes(),
          "accused with a Participant index which wasn't theirs",
        );
        return;
      }

      if !((u16::from(range.start) <= u16::from(faulty)) &&
        (u16::from(faulty) < u16::from(range.end)))
      {
        fatal_slash::<D>(
          txn,
          genesis,
          signed.signer.to_bytes(),
          "accused self of having an InvalidDkgShare",
        );
        return;
      }

      let share = ShareBlame::get(txn, genesis, accuser.into(), faulty.into()).unwrap();
      processors
        .send(
          spec.set().network,
          key_gen::CoordinatorMessage::VerifyBlame {
            id: KeyGenId { set: spec.set(), attempt },
            accuser,
            accused: faulty,
            share,
            blame,
          },
        )
        .await;
    }

    Transaction::DkgConfirmed(attempt, shares, signed) => {
      match handle(
        txn,
        &DataSpecification { topic: Topic::Dkg, label: DKG_CONFIRMATION_SHARES, attempt },
        shares.to_vec(),
        &signed,
      ) {
        Accumulation::Ready(DataSet::Participating(shares)) => {
          log::info!("got all DkgConfirmed for {}", hex::encode(genesis));

          let preprocesses = ConfirmationNonces::get(txn, genesis, attempt).unwrap();
          // TODO: This can technically happen under very very very specific timing as the txn put
          // happens before DkgConfirmed, yet the txn commit isn't guaranteed to
          let key_pair = CurrentlyCompletingKeyPair::get(txn, genesis).expect(
            "in DkgConfirmed handling, which happens after everyone \
              (including us) fires DkgConfirmed, yet no confirming key pair",
          );
          let sig =
            match DkgConfirmer::complete(spec, key, attempt, preprocesses, &key_pair, shares) {
              Ok(sig) => sig,
              Err(p) => {
                fatal_slash_with_participant_index::<D>(spec, txn, p, "invalid DkgConfirmer share");
                return;
              }
            };

          publish_serai_tx(
            spec.set(),
            SeraiValidatorSets::set_keys(spec.set().network, key_pair, Signature(sig)),
          )
          .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {
          panic!("wasn't a participant in DKG confirmination shares")
        }
        Accumulation::NotReady => {}
      }
    }

    Transaction::CosignSubstrateBlock(hash) => {
      AttemptDb::recognize_topic(
        txn,
        genesis,
        Topic::SubstrateSign(SubstrateSignableId::CosigningSubstrateBlock(hash)),
      );
      NonceDecider::handle_substrate_signable(
        txn,
        genesis,
        SubstrateSignableId::CosigningSubstrateBlock(hash),
      );

      let key = loop {
        let Some(key_pair) = KeyPairDb::get(txn, spec.set()) else {
          // This can happen based on a timing condition
          log::warn!("CosignSubstrateBlock yet keys weren't set yet");
          tokio::time::sleep(core::time::Duration::from_secs(1)).await;
          continue;
        };
        break key_pair.0.into();
      };
      let block_number = SeraiBlockNumber::get(txn, hash)
        .expect("CosignSubstrateBlock yet didn't save Serai block number");
      processors
        .send(
          spec.set().network,
          coordinator::CoordinatorMessage::CosignSubstrateBlock {
            id: SubstrateSignId {
              key,
              id: SubstrateSignableId::CosigningSubstrateBlock(hash),
              attempt: 0,
            },
            block_number,
          },
        )
        .await;
    }

    Transaction::Batch(_, batch) => {
      // Because this Batch has achieved synchrony, its batch ID should be authorized
      AttemptDb::recognize_topic(
        txn,
        genesis,
        Topic::SubstrateSign(SubstrateSignableId::Batch(batch)),
      );
      let nonce =
        NonceDecider::handle_substrate_signable(txn, genesis, SubstrateSignableId::Batch(batch));
      recognized_id(spec.set(), genesis, RecognizedIdType::Batch, batch.to_vec(), nonce).await;
    }

    Transaction::SubstrateBlock(block) => {
      let plan_ids = PlanIds::get(txn, &genesis, block).expect(
        "synced a tributary block finalizing a substrate block in a provided transaction \
          despite us not providing that transaction",
      );

      let nonces = NonceDecider::handle_substrate_block(txn, genesis, &plan_ids);
      for (nonce, id) in nonces.into_iter().zip(plan_ids.into_iter()) {
        AttemptDb::recognize_topic(txn, genesis, Topic::Sign(id));
        recognized_id(spec.set(), genesis, RecognizedIdType::Plan, id.to_vec(), nonce).await;
      }
    }

    Transaction::SubstratePreprocess(data) => {
      let Ok(_) = check_sign_data_len::<D>(txn, spec, data.signed.signer, data.data.len()) else {
        return;
      };
      match handle(
        txn,
        &DataSpecification {
          topic: Topic::SubstrateSign(data.plan),
          label: BATCH_PREPROCESS,
          attempt: data.attempt,
        },
        data.data.encode(),
        &data.signed,
      ) {
        Accumulation::Ready(DataSet::Participating(mut preprocesses)) => {
          unflatten(spec, &mut preprocesses);
          NonceDecider::selected_for_signing_substrate(txn, genesis, data.plan);
          let key = KeyPairDb::get(txn, spec.set()).unwrap().0 .0;
          processors
            .send(
              spec.set().network,
              coordinator::CoordinatorMessage::SubstratePreprocesses {
                id: SubstrateSignId { key, id: data.plan, attempt: data.attempt },
                preprocesses,
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {}
        Accumulation::NotReady => {}
      }
    }
    Transaction::SubstrateShare(data) => {
      let Ok(_) = check_sign_data_len::<D>(txn, spec, data.signed.signer, data.data.len()) else {
        return;
      };
      match handle(
        txn,
        &DataSpecification {
          topic: Topic::SubstrateSign(data.plan),
          label: BATCH_SHARE,
          attempt: data.attempt,
        },
        data.data.encode(),
        &data.signed,
      ) {
        Accumulation::Ready(DataSet::Participating(mut shares)) => {
          unflatten(spec, &mut shares);
          let key = KeyPairDb::get(txn, spec.set()).unwrap().0 .0;
          processors
            .send(
              spec.set().network,
              coordinator::CoordinatorMessage::SubstrateShares {
                id: SubstrateSignId { key, id: data.plan, attempt: data.attempt },
                shares: shares
                  .into_iter()
                  .map(|(validator, share)| (validator, share.try_into().unwrap()))
                  .collect(),
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {}
        Accumulation::NotReady => {}
      }
    }

    Transaction::SignPreprocess(data) => {
      let Ok(_) = check_sign_data_len::<D>(txn, spec, data.signed.signer, data.data.len()) else {
        return;
      };
      let key_pair = KeyPairDb::get(txn, spec.set());
      match handle(
        txn,
        &DataSpecification {
          topic: Topic::Sign(data.plan),
          label: SIGN_PREPROCESS,
          attempt: data.attempt,
        },
        data.data.encode(),
        &data.signed,
      ) {
        Accumulation::Ready(DataSet::Participating(mut preprocesses)) => {
          unflatten(spec, &mut preprocesses);
          NonceDecider::selected_for_signing_plan(txn, genesis, data.plan);
          processors
            .send(
              spec.set().network,
              sign::CoordinatorMessage::Preprocesses {
                id: SignId {
                  key: key_pair
                    .expect("completed SignPreprocess despite not setting the key pair")
                    .1
                    .into(),
                  id: data.plan,
                  attempt: data.attempt,
                },
                preprocesses,
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {}
        Accumulation::NotReady => {}
      }
    }
    Transaction::SignShare(data) => {
      let Ok(_) = check_sign_data_len::<D>(txn, spec, data.signed.signer, data.data.len()) else {
        return;
      };
      let key_pair = KeyPairDb::get(txn, spec.set());
      match handle(
        txn,
        &DataSpecification {
          topic: Topic::Sign(data.plan),
          label: SIGN_SHARE,
          attempt: data.attempt,
        },
        data.data.encode(),
        &data.signed,
      ) {
        Accumulation::Ready(DataSet::Participating(mut shares)) => {
          unflatten(spec, &mut shares);
          processors
            .send(
              spec.set().network,
              sign::CoordinatorMessage::Shares {
                id: SignId {
                  key: key_pair
                    .expect("completed SignShares despite not setting the key pair")
                    .1
                    .into(),
                  id: data.plan,
                  attempt: data.attempt,
                },
                shares,
              },
            )
            .await;
        }
        Accumulation::Ready(DataSet::NotParticipating) => {}
        Accumulation::NotReady => {}
      }
    }
    Transaction::SignCompleted { plan, tx_hash, first_signer, signature: _ } => {
      log::info!(
        "on-chain SignCompleted claims {} completes {}",
        hex::encode(&tx_hash),
        hex::encode(plan)
      );

      if AttemptDb::attempt(txn, genesis, Topic::Sign(plan)).is_none() {
        fatal_slash::<D>(
          txn,
          genesis,
          first_signer.to_bytes(),
          "claimed an unrecognized plan was completed",
        );
        return;
      };

      // TODO: Confirm this signer hasn't prior published a completion
      let Some(key_pair) = KeyPairDb::get(txn, spec.set()) else {
        panic!("SignCompleted for recognized plan ID despite not having a key pair for this set")
      };
      processors
        .send(
          spec.set().network,
          sign::CoordinatorMessage::Completed { key: key_pair.1.to_vec(), id: plan, tx: tx_hash },
        )
        .await;
    }
  }
}