more checking that various functions match v0.1; some variable/etc renaming; fix is_double_vote to check epoch, not slot equivalence; finish verify_slashable_attestation; adjust is_surround_vote logic (#100)

beacon_chain/spec/beaconstate.nim

@@ -10,11 +10,10 @@ import
   ../extras, ../ssz,
   ./crypto, ./datatypes, ./digest, ./helpers, ./validator
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_effective_balance
 func get_effective_balance*(state: BeaconState, index: ValidatorIndex): uint64 =
-  # Validators collect rewards which increases their balance but not their
+  ## Return the effective balance (also known as "balance at stake") for a
-  # influence. Validators may also lose balance if they fail to do their duty
+  ## validator with the given ``index``.
-  # in which case their influence decreases. Once they drop below a certain
-  # balance, they're removed from the validator registry.
   min(state.validator_balances[index], MAX_DEPOSIT_AMOUNT)
 
 func sum_effective_balances*(
@@ -82,6 +81,7 @@ func process_deposit(state: var BeaconState,
 
     state.validator_balances[index] += amount
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_entry_exit_effect_epoch
 func get_entry_exit_effect_epoch*(epoch: EpochNumber): EpochNumber =
   ## An entry or exit triggered in the ``epoch`` given by the input takes effect at
   ## the epoch given by the output.
@@ -222,13 +222,15 @@ func get_block_root*(state: BeaconState,
   doAssert slot < state.slot
   state.latest_block_roots[slot mod LATEST_BLOCK_ROOTS_LENGTH]
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_attestation_participants
 func get_attestation_participants*(state: BeaconState,
                                    attestation_data: AttestationData,
-                                   aggregation_bitfield: seq[byte]): seq[ValidatorIndex] =
+                                   bitfield: seq[byte]): seq[ValidatorIndex] =
   ## Attestation participants in the attestation data are called out in a
   ## bit field that corresponds to the committee of the shard at the time - this
   ## function converts it to list of indices in to BeaconState.validators
   ## Returns empty list if the shard is not found
+  ## Return the participant indices at for the ``attestation_data`` and ``bitfield``.
   # TODO Linear search through shard list? borderline ok, it's a small list
   # TODO bitfield type needed, once bit order settles down
   # TODO iterator candidate
@@ -243,12 +245,13 @@ func get_attestation_participants*(state: BeaconState,
   let crosslink_committee = mapIt(
     filterIt(crosslink_committees, it.shard == attestation_data.shard),
     it.committee)[0]
-  assert len(aggregation_bitfield) == (len(crosslink_committee) + 7) div 8
+
+  assert verify_bitfield(bitfield, len(crosslink_committee))
 
   # Find the participating attesters in the committee
   result = @[]
   for i, validator_index in crosslink_committee:
-    let aggregation_bit = (aggregation_bitfield[i div 8] shr (7 - (i mod 8))) mod 2
+    let aggregation_bit = get_bitfield_bit(bitfield, i)
     if aggregation_bit == 1:
       result.add(validator_index)
 

beacon_chain/spec/crypto.nim

@@ -73,14 +73,25 @@ func bls_aggregate_pubkeys*(keys: openArray[ValidatorPubKey]): ValidatorPubKey =
     else:
       result.combine(key)
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/bls_signature.md#bls_verify
 func bls_verify*(
     pubkey: ValidatorPubKey, msg: openArray[byte], sig: ValidatorSig,
     domain: uint64): bool =
   # name from spec!
   sig.verify(msg, domain, pubkey)
 
-func bls_sign*(key: ValidatorPrivKey,
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/bls_signature.md#bls_verify_multiple
-               msg: openarray[byte], domain: uint64): ValidatorSig =
+func bls_verify_multiple*(
+    pubkeys: seq[ValidatorPubKey], messages: seq[array[0..31, byte]],
+    sig: ValidatorSig, domain: uint64): bool =
+  let L = len(pubkeys)
+  assert L == len(messages)
+
+  # TODO calculate product of ate pairings; check how sig.verify works
+  true
+
+func bls_sign*(key: ValidatorPrivKey, msg: openarray[byte],
+               domain: uint64): ValidatorSig =
   # name from spec!
   key.sign(domain, msg)
 

beacon_chain/spec/datatypes.nim

@@ -229,7 +229,7 @@ type
   # https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#attestationdata
   AttestationDataAndCustodyBit* = object
     data*: AttestationData
-    custody_bit: bool
+    custody_bit*: bool
 
   # https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#deposit
   Deposit* = object

beacon_chain/spec/helpers.nim

@@ -14,13 +14,13 @@ import ./datatypes, ./digest, sequtils, math
 func bitSet*(bitfield: var openArray[byte], index: int) =
   bitfield[index div 8] = bitfield[index div 8] or 1'u8 shl (7 - (index mod 8))
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_bitfield_bit
 func get_bitfield_bit*(bitfield: openarray[byte], i: int): byte =
-  # https://github.com/ethereum/eth2.0-specs/blob/dev/specs/core/0_beacon-chain.md#get_bitfield_bit
   # Extract the bit in ``bitfield`` at position ``i``.
   (bitfield[i div 8] shr (7 - (i mod 8))) mod 2
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#verify_bitfield
 func verify_bitfield*(bitfield: openarray[byte], committee_size: int): bool =
-  # https://github.com/ethereum/eth2.0-specs/blob/dev/specs/core/0_beacon-chain.md#verify_bitfield
   # Verify ``bitfield`` against the ``committee_size``.
   if len(bitfield) != (committee_size + 7) div 8:
     return false
@@ -113,6 +113,7 @@ func repeat_hash*(v: Eth2Digest, n: SomeInteger): Eth2Digest =
     result = eth2hash(result.data)
     dec n
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#integer_squareroot
 func integer_squareroot*(n: SomeInteger): SomeInteger =
   ## The largest integer ``x`` such that ``x**2`` is less than ``n``.
   var
@@ -123,12 +124,15 @@ func integer_squareroot*(n: SomeInteger): SomeInteger =
     y = (x + n div x) div 2
   x
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_fork_version
 func get_fork_version*(fork: Fork, epoch: EpochNumber): uint64 =
+  ## Return the fork version of the given ``epoch``.
   if epoch < fork.epoch:
     fork.previous_version
   else:
     fork.current_version
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_domain
 func get_domain*(
     fork: Fork, epoch: EpochNumber, domain_type: SignatureDomain): uint64 =
   # TODO Slot overflow? Or is slot 32 bits for all intents and purposes?
@@ -151,37 +155,31 @@ func merkle_root*(values: openArray[Eth2Digest]): Eth2Digest =
   #TODO
   discard
 
-proc is_double_vote*(attestation_data_1: AttestationData,
-                     attestation_data_2: AttestationData): bool =
-  ## Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``.
-  ## Returns True if the provided ``AttestationData`` are slashable
-  ## due to a 'double vote'.
-  ## A double vote is when a validator votes for two attestations within the
-  ## same slot - doing so means risking getting slashed.
-  attestation_data_1.slot == attestation_data_2.slot
-
 # https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#slot_to_epoch
 func slot_to_epoch*(slot: SlotNumber): EpochNumber =
   slot div EPOCH_LENGTH
 
-proc is_surround_vote*(attestation_data_1: AttestationData,
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#is_double_vote
+func is_double_vote*(attestation_data_1: AttestationData,
+                     attestation_data_2: AttestationData): bool =
+  ## Check if ``attestation_data_1`` and ``attestation_data_2`` have the same
+  ## target.
+  let
+    target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
+    target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
+  target_epoch_1 == target_epoch_2
+
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#is_surround_vote
+func is_surround_vote*(attestation_data_1: AttestationData,
                        attestation_data_2: AttestationData): bool =
-  ## Assumes ``attestation_data_1`` is distinct from ``attestation_data_2``.
+  ## Check if ``attestation_data_1`` surrounds ``attestation_data_2``.
-  ## Returns True if the provided ``AttestationData`` are slashable
-  ## due to a 'surround vote'.
-  ## Note: parameter order matters as this function only checks
-  ## that ``attestation_data_1`` surrounds ``attestation_data_2``.
   let
     source_epoch_1 = attestation_data_1.justified_epoch
     source_epoch_2 = attestation_data_2.justified_epoch
     target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
     target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
 
-  (
+  source_epoch_1 < source_epoch_2 and target_epoch_2 < target_epoch_1
-    (source_epoch_1 < source_epoch_2) and
-    (source_epoch_2 + 1 == target_epoch_2) and
-    (target_epoch_2 < target_epoch_1)
-  )
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#is_active_validator
 func is_active_validator*(validator: Validator, epoch: EpochNumber): bool =

beacon_chain/state_transition.nim

@@ -184,8 +184,8 @@ proc processProposerSlashings(
 
   return true
 
+# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#verify_slashable_attestation
 func verify_slashable_attestation(state: BeaconState, slashable_attestation: SlashableAttestation): bool =
-  # https://github.com/ethereum/eth2.0-specs/blob/dev/specs/core/0_beacon-chain.md#verify_slashable_attestation
   # Verify validity of ``slashable_attestation`` fields.
 
   if anyIt(slashable_attestation.custody_bitfield, it != 0):   # [TO BE REMOVED IN PHASE 1]
@@ -208,7 +208,31 @@ func verify_slashable_attestation(state: BeaconState, slashable_attestation: Sla
     custody_bit_0_indices: seq[uint64] = @[]
     custody_bit_1_indices: seq[uint64] = @[]
 
-  return true
+  for i, validator_index in slashable_attestation.validator_indices:
+    if get_bitfield_bit(slashable_attestation.custody_bitfield, i) == 0b0:
+      custody_bit_0_indices.add(validator_index)
+    else:
+      custody_bit_1_indices.add(validator_index)
+
+  # bug in 0.1 version of spec, fixed later; bls_verify is what works
+  bls_verify_multiple(
+    @[
+      bls_aggregate_pubkeys(mapIt(custody_bit_0_indices, state.validator_registry[it.int].pubkey)),
+      bls_aggregate_pubkeys(mapIt(custody_bit_1_indices, state.validator_registry[it.int].pubkey)),
+    ],
+    @[
+      hash_tree_root(AttestationDataAndCustodyBit(
+        data: slashable_attestation.data, custody_bit: false)),
+      hash_tree_root(AttestationDataAndCustodyBit(
+        data: slashable_attestation.data, custody_bit: true)),
+    ],
+    slashable_attestation.aggregate_signature,
+    get_domain(
+      state.fork,
+      slot_to_epoch(slashable_attestation.data.slot),
+      DOMAIN_ATTESTATION,
+    ),
+  )
 
 proc processAttesterSlashings(state: var BeaconState, blck: BeaconBlock): bool =
   ## https://github.com/ethereum/eth2.0-specs/blob/dev/specs/core/0_beacon-chain.md#attester-slashings-1