Merge pull request #2030 from lsankar4033/more_gossip_validations

Two more gossip validations

specs/phase0/p2p-interface.md

@@ -383,6 +383,7 @@ The `beacon_attestation_{subnet_id}` topics are used to propagate unaggregated a
 to the subnet `subnet_id` (typically beacon and persistent committees) to be aggregated before being gossiped to `beacon_aggregate_and_proof`.
 
 The following validations MUST pass before forwarding the `attestation` on the subnet.
+- _[REJECT]_ The committee index is within the expected range -- i.e. `data.index < get_committee_count_per_slot(state, data.target.epoch)`.
 - _[REJECT]_ The attestation is for the correct subnet --
   i.e. `compute_subnet_for_attestation(committees_per_slot, attestation.data.slot, attestation.data.index) == subnet_id`,
   where `committees_per_slot = get_committee_count_per_slot(state, attestation.data.target.epoch)`,
@@ -395,6 +396,8 @@ The following validations MUST pass before forwarding the `attestation` on the s
   compute_epoch_at_slot(attestation.data.slot)`
 - _[REJECT]_ The attestation is unaggregated --
   that is, it has exactly one participating validator (`len([bit for bit in attestation.aggregation_bits if bit]) == 1`, i.e. exactly 1 bit is set).
+- _[REJECT]_ The number of aggregation bits matches the committee size -- i.e.
+  `len(attestation.aggregation_bits) == len(get_beacon_committee(state, data.slot, data.index))`.
 - _[IGNORE]_ There has been no other valid attestation seen on an attestation subnet
   that has an identical `attestation.data.target.epoch` and participating validator index.
 - _[REJECT]_ The signature of `attestation` is valid.
@@ -410,7 +413,6 @@ The following validations MUST pass before forwarding the `attestation` on the s
 
 
 
-
 #### Attestations and Aggregation
 
 Attestation broadcasting is grouped into subnets defined by a topic.