nimbus-eth2/beacon_chain/spec/signatures_batch.nim

# beacon_chain
# Copyright (c) 2018-2022 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.

{.push raises: [Defect].}

## This module contains signature verification helpers corresponding to those
## in signatures.nim, for use with signature sets / batch signature verification
## The functions follow the same structure and use the same arguments, except
## that the flow is split into separate collection and verification steps.

import
  # Status lib
  blscurve,
  stew/[byteutils, results],
  taskpools,
  bearssl/rand,
  # Internal
  "."/[helpers, beaconstate, forks, signatures],
  "."/datatypes/[altair, bellatrix, phase0]

export results, rand, altair, phase0, taskpools, signatures

type
  TaskPoolPtr* = Taskpool

  BatchVerifier* = object
    sigVerifCache*: BatchedBLSVerifierCache ##\
    ## A cache for batch BLS signature verification contexts
    rng*: ref HmacDrbgContext  ##\
    ## A reference to the Nimbus application-wide RNG

    taskpool*: TaskPoolPtr

func `$`*(s: SignatureSet): string =
  "(pubkey: 0x" & s.pubkey.toHex() &
    ", signing_root: 0x" & s.message.toHex() &
    ", signature: 0x" & s.signature.toHex() & ')'

# Important:
#   - Due to lazy loading, when we do crypto verification
#     and only then state-transition verification,
#     there is no guarantee that pubkeys and signatures received are valid
#     unlike when Nimbus did eager loading which ensured they were correct beforehand

template loadOrExit(signature: ValidatorSig, error: cstring):
    untyped =
  ## Load a BLS signature from a raw signature
  ## Exits the **caller** with false if the signature is invalid
  let sig = signature.load()
  if sig.isNone:
    return err(error) # this exits the calling scope, as templates are inlined.
  sig.unsafeGet()

func init(T: type SignatureSet,
    pubkey: CookedPubKey, signing_root: Eth2Digest,
    signature: CookedSig): T =
  ## Add a new signature set triplet (pubkey, message, signature)
  ## to a collection of signature sets for batch verification.
  (
    blscurve.PublicKey(pubkey),
    signing_root.data,
    blscurve.Signature(signature)
  )

proc aggregateAttesters(
      validatorIndices: openArray[uint64|ValidatorIndex],
      validatorKeys: auto,
     ): Result[CookedPubKey, cstring] =
  if validatorIndices.len == 0:
    # Aggregation spec requires non-empty collection
    # - https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04
    # Eth2 spec requires at least one attesting index in attestation
    # - https://github.com/ethereum/consensus-specs/blob/v1.2.0-rc.1/specs/phase0/beacon-chain.md#is_valid_indexed_attestation
    return err("aggregateAttesters: no attesting indices")

  let
    firstKey = validatorKeys.load(validatorIndices[0])

  if not firstKey.isSome():
    return err("aggregateAttesters: invalid attesting index")

  var attestersAgg{.noinit.}: AggregatePublicKey

  attestersAgg.init(firstKey.get())
  for i in 1 ..< validatorIndices.len:
    let key = validatorKeys.load(validatorIndices[i])
    if not key.isSome():
      return err("aggregateAttesters: invalid attesting index")
    attestersAgg.aggregate(key.get())

  ok(finish(attestersAgg))

proc aggregateAttesters(
      validatorIndices: openArray[uint64|ValidatorIndex],
      bits: auto,
      validatorKeys: auto,
     ): Result[CookedPubKey, cstring] =
  if validatorIndices.len == 0:
    # Aggregation spec requires non-empty collection
    # - https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04
    # Eth2 spec requires at least one attesting index in attestation
    # - https://github.com/ethereum/consensus-specs/blob/v1.2.0-rc.1/specs/phase0/beacon-chain.md#is_valid_indexed_attestation
    return err("aggregateAttesters: no attesting indices")

  var attestersAgg{.noinit.}: AggregatePublicKey

  var inited = false
  for i in 0..<bits.len:
    if bits[i]:
      let key = validatorKeys.load(validatorIndices[i])
      if not key.isSome():
        return err("aggregateAttesters: invalid attesting index")
      if inited:
        attestersAgg.aggregate(key.get())
      else:
        attestersAgg = AggregatePublicKey.init(key.get)
        inited = true

  if not inited:
    return err("aggregateAttesters:no attesting indices")

  ok(finish(attestersAgg))

# Public API
# ------------------------------------------------------

# See also: verify_slot_signature
proc slot_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest, slot: Slot,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_slot_signing_root(
    fork, genesis_validators_root, slot)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_epoch_signature
proc epoch_signature_set*(
   fork: Fork, genesis_validators_root: Eth2Digest, epoch: Epoch,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_epoch_signing_root(
    fork, genesis_validators_root, epoch)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_block_signature
proc block_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest, slot: Slot,
    blck: Eth2Digest | SomeForkyBeaconBlock | BeaconBlockHeader,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_block_signing_root(
    fork, genesis_validators_root, slot, blck)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_aggregate_and_proof_signature
proc aggregate_and_proof_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    aggregate_and_proof: AggregateAndProof,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_aggregate_and_proof_signing_root(
    fork, genesis_validators_root, aggregate_and_proof)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_attestation_signature
proc attestation_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    attestation_data: AttestationData,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_attestation_signing_root(
    fork, genesis_validators_root, attestation_data)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_voluntary_exit_signature
proc voluntary_exit_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    voluntary_exit: VoluntaryExit,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_voluntary_exit_signing_root(
    fork, genesis_validators_root, voluntary_exit)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_sync_committee_message_signature
proc sync_committee_message_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    slot: Slot, block_root: Eth2Digest,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_sync_committee_message_signing_root(
    fork, genesis_validators_root, slot, block_root)

  SignatureSet.init(pubkey, signing_root, signature)

# See also: verify_sync_committee_selection_proof
proc sync_committee_selection_proof_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    slot: Slot, subcommittee_index: SyncSubcommitteeIndex,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_sync_committee_selection_proof_signing_root(
    fork, genesis_validators_root, slot, subcommittee_index)

  SignatureSet.init(pubkey, signing_root, signature)

proc contribution_and_proof_signature_set*(
    fork: Fork, genesis_validators_root: Eth2Digest,
    msg: ContributionAndProof,
    pubkey: CookedPubKey, signature: CookedSig): SignatureSet =
  let signing_root = compute_contribution_and_proof_signing_root(
    fork, genesis_validators_root, msg)

  SignatureSet.init(pubkey, signing_root, signature)

proc collectSignatureSets*(
       sigs: var seq[SignatureSet],
       signed_block: ForkySignedBeaconBlock,
       validatorKeys: auto,
       state: ForkedHashedBeaconState,
       cache: var StateCache): Result[void, cstring] =
  ## Collect all signature verifications that process_block would normally do
  ## except deposits, in one go.
  ##
  ## This includes
  ## - Block proposer
  ## - Randao Reaveal
  ## - Proposer slashings
  ## - Attester slashings
  ## - Attestations
  ## - VoluntaryExits
  ## - SyncCommittee (altair+)
  ##
  ## We do not include deposits as they can be invalid while still leaving the
  ## block valid

  # Metadata
  # ----------------------------------------------------
  mixin load

  let
    fork = getStateField(state, fork)
    genesis_validators_root = getStateField(state, genesis_validators_root)

  let
    proposer_index = signed_block.message.proposer_index
    proposer_key = validatorKeys.load(proposer_index)
  if not proposer_key.isSome():
    return err("collectSignatureSets: invalid proposer index")

  let epoch = signed_block.message.slot.epoch()

  # 1. Block proposer
  # ----------------------------------------------------
  sigs.add block_signature_set(
    fork, genesis_validators_root,
    signed_block.message.slot, signed_block.root,
    proposer_key.get(), signed_block.signature.loadOrExit(
      "collectSignatureSets: cannot load signature"))

  # 2. Randao Reveal
  # ----------------------------------------------------
  sigs.add epoch_signature_set(
    fork, genesis_validators_root, epoch, proposer_key.get(),
    signed_block.message.body.randao_reveal.loadOrExit(
      "collectSignatureSets: cannot load randao"))

  # 3. Proposer slashings
  # ----------------------------------------------------
  # Denial-of-service:
  #   SSZ deserialization guarantees that blocks received from random sources
  #   including peer or RPC
  #   have at most MAX_PROPOSER_SLASHINGS proposer slashings.
  for i in 0 ..< signed_block.message.body.proposer_slashings.len:
    # don't use "items" for iterating over large type
    # due to https://github.com/nim-lang/Nim/issues/14421
    # fixed in 1.4.2

    # Alias
    template slashing: untyped = signed_block.message.body.proposer_slashings[i]

    # Proposed block 1
    block:
      let
        header = slashing.signed_header_1
        key = validatorKeys.load(header.message.proposer_index)
      if not key.isSome():
        return err("collectSignatureSets: invalid slashing proposer index 1")

      sigs.add block_signature_set(
        fork, genesis_validators_root, header.message.slot, header.message,
        key.get(), header.signature.loadOrExit(
          "collectSignatureSets: cannot load proposer slashing 1 signature"))

    # Conflicting block 2
    block:
      let
        header = slashing.signed_header_2
        key = validatorKeys.load(header.message.proposer_index)
      if not key.isSome():
        return err("collectSignatureSets: invalid slashing proposer index 2")

      sigs.add block_signature_set(
        fork, genesis_validators_root, header.message.slot, header.message,
        key.get(), header.signature.loadOrExit(
          "collectSignatureSets: cannot load proposer slashing 2 signature"))

  # 4. Attester slashings
  # ----------------------------------------------------
  # Denial-of-service:
  #   SSZ deserialization guarantees that blocks received from random sources
  #   including peer or RPC
  #   have at most MAX_ATTESTER_SLASHINGS attester slashings.
  for i in 0 ..< signed_block.message.body.attester_slashings.len:
    # don't use "items" for iterating over large type
    # due to https://github.com/nim-lang/Nim/issues/14421
    # fixed in 1.4.2

    # Alias
    template slashing: untyped = signed_block.message.body.attester_slashings[i]

    # Attestation 1
    block:
      let
        key = ? aggregateAttesters(
          slashing.attestation_1.attesting_indices.asSeq(), validatorKeys)
        sig = slashing.attestation_1.signature.loadOrExit("")
      sigs.add attestation_signature_set(
        fork, genesis_validators_root, slashing.attestation_1.data, key, sig)

    # Conflicting attestation 2
    block:
      let
        key = ? aggregateAttesters(
          slashing.attestation_2.attesting_indices.asSeq(), validatorKeys)
        sig = slashing.attestation_2.signature.loadOrExit("")
      sigs.add attestation_signature_set(
        fork, genesis_validators_root, slashing.attestation_2.data, key, sig)

  # 5. Attestations
  # ----------------------------------------------------
  # Denial-of-service:
  #   SSZ deserialization guarantees that blocks received from random sources
  #   including peer or RPC
  #   have at most MAX_ATTESTATIONS attestations.
  for i in 0 ..< signed_block.message.body.attestations.len:
    # don't use "items" for iterating over large type
    # due to https://github.com/nim-lang/Nim/issues/14421
    # fixed in 1.4.2
    template attestation: untyped = signed_block.message.body.attestations[i]

    let
      key = ? aggregateAttesters(
        get_attesting_indices(
          state, attestation.data, attestation.aggregation_bits, cache),
        validatorKeys)
      sig = attestation.signature.loadOrExit("")

    sigs.add attestation_signature_set(
      fork, genesis_validators_root, attestation.data, key, sig)

  # 6. VoluntaryExits
  # ----------------------------------------------------
  # Denial-of-service:
  #   SSZ deserialization guarantees that blocks received from random sources
  #   including peer or RPC
  #   have at most MAX_VOLUNTARY_EXITS voluntary exits.
  for i in 0 ..< signed_block.message.body.voluntary_exits.len:
    # don't use "items" for iterating over large type
    # due to https://github.com/nim-lang/Nim/issues/14421
    # fixed in 1.4.2
    template volex: untyped = signed_block.message.body.voluntary_exits[i]
    let key = validatorKeys.load(volex.message.validator_index)
    if not key.isSome():
      return err("collectSignatureSets: invalid voluntary exit")

    sigs.add voluntary_exit_signature_set(
      fork, genesis_validators_root, volex.message, key.get(),
      volex.signature.loadOrExit(
        "collectSignatureSets: cannot load voluntary exit signature"))

  block:
    # 7. SyncAggregate
    # ----------------------------------------------------
    withState(state):
      when stateFork >= BeaconStateFork.Altair and
          (signed_block is altair.SignedBeaconBlock or
            signed_block is bellatrix.SignedBeaconBlock):
        if signed_block.message.body.sync_aggregate.sync_committee_bits.countOnes() == 0:
          if signed_block.message.body.sync_aggregate.sync_committee_signature != ValidatorSig.infinity():
            return err("collectSignatureSets: empty sync aggregates need signature of point at infinity")
        else:
          let
            current_sync_committee =
              state.data.get_sync_committee_cache(cache).current_sync_committee
            previous_slot = max(state.data.slot, Slot(1)) - 1
            beacon_block_root = get_block_root_at_slot(state.data, previous_slot)
            pubkey = ? aggregateAttesters(
              current_sync_committee,
              signed_block.message.body.sync_aggregate.sync_committee_bits,
              validatorKeys)

          sigs.add sync_committee_message_signature_set(
            fork, genesis_validators_root, previous_slot, beacon_block_root,
            pubkey,
            signed_block.message.body.sync_aggregate.sync_committee_signature.loadOrExit(
              "collectSignatureSets: cannot load signature"))

  ok()

proc batchVerify*(verifier: var BatchVerifier, sigs: openArray[SignatureSet]): bool =
  let bytes = verifier.rng[].generate(array[32, byte])
  try:
    verifier.taskpool.batchVerify(verifier.sigVerifCache, sigs, bytes)
  except Exception as exc:
    raiseAssert exc.msg # Shouldn't happen