From a6e825d46056a4a92473e52f1ea0bcb19210e67b Mon Sep 17 00:00:00 2001
From: Justin <drakefjustin@gmail.com>
Date: Sun, 5 May 2019 12:04:34 +0100
Subject: [PATCH 1/8] Update 0_beacon-chain.md

---
 specs/core/0_beacon-chain.md | 56 +++++++++++++++---------------------
 1 file changed, 23 insertions(+), 33 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 36ac927961..addaa865ee 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -279,6 +279,8 @@ The types are defined topologically to aid in facilitating an executable version
 
 ```python
 {
+    # Shard number
+    'shard': 'uint64',
     # Epoch number
     'epoch': 'uint64',
     # Root of the previous crosslink
@@ -315,9 +317,7 @@ The types are defined topologically to aid in facilitating an executable version
     'target_root': 'bytes32',
 
     # Crosslink vote
-    'shard': 'uint64',
-    'previous_crosslink_root': 'bytes32',
-    'crosslink_data_root': 'bytes32',
+    'crosslink': Crosslink,
 }
 ```
 
@@ -765,7 +765,7 @@ def get_epoch_start_shard(state: BeaconState, epoch: Epoch) -> Shard:
 def get_attestation_slot(state: BeaconState, attestation: Attestation) -> Slot:
     epoch = attestation.data.target_epoch
     committee_count = get_epoch_committee_count(state, epoch)
-    offset = (attestation.data.shard + SHARD_COUNT - get_epoch_start_shard(state, epoch)) % SHARD_COUNT
+    offset = (attestation.data.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, epoch)) % SHARD_COUNT
     return get_epoch_start_slot(epoch) + offset // (committee_count // SLOTS_PER_EPOCH)
 ```
 
@@ -927,7 +927,7 @@ def get_attesting_indices(state: BeaconState,
     """
     Return the sorted attesting indices corresponding to ``attestation_data`` and ``bitfield``.
     """
-    committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.shard)
+    committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.crosslink.shard)
     assert verify_bitfield(bitfield, len(committee))
     return sorted([index for i, index in enumerate(committee) if get_bitfield_bit(bitfield, i) == 0b1])
 ```
@@ -1296,28 +1296,18 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
     return get_total_balance(state, get_unslashed_attesting_indices(state, attestations))
 ```
 
-```python
-def get_crosslink_from_attestation_data(state: BeaconState, data: AttestationData) -> Crosslink:
-    return Crosslink(
-        epoch=min(data.target_epoch, state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
-        previous_crosslink_root=data.previous_crosslink_root,
-        crosslink_data_root=data.crosslink_data_root,
-    )
-```
-
 ```python
 def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
-    shard_attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.shard == shard]
-    shard_crosslinks = [get_crosslink_from_attestation_data(state, a.data) for a in shard_attestations]
+    shard_attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.crosslink.shard == shard]
     candidate_crosslinks = [
-        c for c in shard_crosslinks
+        c for c in [a.data.crosslink for a in shard_attestations]
         if hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c))
     ]
     if len(candidate_crosslinks) == 0:
         return Crosslink(), []
 
     def get_attestations_for(crosslink: Crosslink) -> List[PendingAttestation]:
-        return [a for a in shard_attestations if get_crosslink_from_attestation_data(state, a.data) == crosslink]
+        return [a for a in shard_attestations if a.data.crosslink == crosslink]
     # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
     winning_crosslink = max(candidate_crosslinks, key=lambda crosslink: (
         get_attesting_balance(state, get_attestations_for(crosslink)), crosslink.crosslink_data_root
@@ -1705,30 +1695,30 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     attestation_slot = get_attestation_slot(state, attestation)
     assert attestation_slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= attestation_slot + SLOTS_PER_EPOCH
 
-    # Check target epoch, source epoch, source root, and source crosslink
     data = attestation.data
-    assert (data.target_epoch, data.source_epoch, data.source_root, data.previous_crosslink_root) in {
-        (get_current_epoch(state), state.current_justified_epoch, state.current_justified_root, hash_tree_root(state.current_crosslinks[data.shard])),
-        (get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root, hash_tree_root(state.previous_crosslinks[data.shard])),
-    }
-
-    # Check crosslink data root
-    assert data.crosslink_data_root == ZERO_HASH  # [to be removed in phase 1]
-
-    # Check signature and bitfields
-    assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
-
-    # Cache pending attestation
     pending_attestation = PendingAttestation(
         data=data,
         aggregation_bitfield=attestation.aggregation_bitfield,
         inclusion_delay=state.slot - attestation_slot,
         proposer_index=get_beacon_proposer_index(state),
     )
+
+    assert data.target_epoch in (get_previous_epoch(state), get_current_epoch(state))
+    if data.target_epoch == get_previous_epoch(state):
+        ffg_data = (state.previous_justified_epoch, state.previous_justified_root, get_previous_epoch(state))
+        previous_crosslink = state.previous_crosslinks[data.crosslink.shard]
+        state.previous_epoch_attestations.append(pending_attestation)
     if data.target_epoch == get_current_epoch(state):
+        ffg_data = (state.current_justified_epoch, state.current_justified_root, get_current_epoch(state))
+        previous_crosslink = state.current_crosslinks[data.crosslink.shard]
         state.current_epoch_attestations.append(pending_attestation)
-    else:
-        state.previous_epoch_attestations.append(pending_attestation)
+
+    # Check FFG data, crosslink data, and signature
+    assert ffg_data == (data.source_epoch, data.source_root, data.target_epoch)
+    assert data.crosslink.epoch == min(data.target_epoch, previous_crosslink.epoch + MAX_CROSSLINK_EPOCHS)
+    assert data.crosslink.previous_crosslink_root == hash_tree_root(previous_crosslink)
+    assert data.crosslink.crosslink_data_root == ZERO_HASH  # [to be removed in phase 1]
+    assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
 ```
 
 ##### Deposits

From 5fb32fd19b780d172e8738d887fd0675df7ec3ef Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Sun, 5 May 2019 12:10:39 +0100
Subject: [PATCH 2/8] Fix tests

---
 configs/constant_presets/mainnet.yaml            |  4 ++--
 configs/constant_presets/minimal.yaml            |  4 ++--
 specs/core/0_beacon-chain.md                     |  6 +++---
 specs/core/1_custody-game.md                     | 16 ++++++++--------
 specs/core/1_shard-data-chains.md                | 16 ++++++++--------
 specs/validator/0_beacon-chain-validator.md      |  4 ++--
 .../block_processing/test_process_attestation.py |  4 ++--
 .../epoch_processing/test_process_crosslinks.py  | 12 ++++++------
 test_libs/pyspec/tests/helpers.py                | 15 ++++++++++-----
 9 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/configs/constant_presets/mainnet.yaml b/configs/constant_presets/mainnet.yaml
index 72d0fdc8f2..6ac3f422f5 100644
--- a/configs/constant_presets/mainnet.yaml
+++ b/configs/constant_presets/mainnet.yaml
@@ -72,7 +72,7 @@ MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
 # 2**11 (= 2,048) epochs 9 days
 PERSISTENT_COMMITTEE_PERIOD: 2048
 # 2**6 (= 64) epochs ~7 hours
-MAX_CROSSLINK_EPOCHS: 64
+MAX_EPOCHS_PER_CROSSLINK: 64
 # 2**2 (= 4) epochs 25.6 minutes
 MIN_EPOCHS_TO_INACTIVITY_PENALTY: 4
 
@@ -124,4 +124,4 @@ DOMAIN_RANDAO: 1
 DOMAIN_ATTESTATION: 2
 DOMAIN_DEPOSIT: 3
 DOMAIN_VOLUNTARY_EXIT: 4
-DOMAIN_TRANSFER: 5
\ No newline at end of file
+DOMAIN_TRANSFER: 5
diff --git a/configs/constant_presets/minimal.yaml b/configs/constant_presets/minimal.yaml
index 0a6cab6872..caae4623ba 100644
--- a/configs/constant_presets/minimal.yaml
+++ b/configs/constant_presets/minimal.yaml
@@ -71,7 +71,7 @@ MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
 # 2**11 (= 2,048) epochs 9 days
 PERSISTENT_COMMITTEE_PERIOD: 2048
 # 2**6 (= 64) epochs ~7 hours
-MAX_CROSSLINK_EPOCHS: 64
+MAX_EPOCHS_PER_CROSSLINK: 64
 # 2**2 (= 4) epochs 25.6 minutes
 MIN_EPOCHS_TO_INACTIVITY_PENALTY: 4
 
@@ -123,4 +123,4 @@ DOMAIN_RANDAO: 1
 DOMAIN_ATTESTATION: 2
 DOMAIN_DEPOSIT: 3
 DOMAIN_VOLUNTARY_EXIT: 4
-DOMAIN_TRANSFER: 5
\ No newline at end of file
+DOMAIN_TRANSFER: 5
diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index addaa865ee..156a2523d2 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -206,10 +206,10 @@ These configurations are updated for releases, but may be out of sync during `de
 | `SLOTS_PER_HISTORICAL_ROOT` | `2**13` (= 8,192) | slots | ~13 hours |
 | `MIN_VALIDATOR_WITHDRAWABILITY_DELAY` | `2**8` (= 256) | epochs | ~27 hours |
 | `PERSISTENT_COMMITTEE_PERIOD` | `2**11` (= 2,048)  | epochs | 9 days  |
-| `MAX_CROSSLINK_EPOCHS` | `2**6` (= 64) | epochs | ~7 hours |
+| `MAX_EPOCHS_PER_CROSSLINK` | `2**6` (= 64) | epochs | ~7 hours |
 | `MIN_EPOCHS_TO_INACTIVITY_PENALTY` | `2**2` (= 4) | epochs | 25.6 minutes |
 
-* `MAX_CROSSLINK_EPOCHS` should be a small constant times `SHARD_COUNT // SLOTS_PER_EPOCH`
+* `MAX_EPOCHS_PER_CROSSLINK` should be a small constant times `SHARD_COUNT // SLOTS_PER_EPOCH`
 
 ### State list lengths
 
@@ -1715,7 +1715,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
 
     # Check FFG data, crosslink data, and signature
     assert ffg_data == (data.source_epoch, data.source_root, data.target_epoch)
-    assert data.crosslink.epoch == min(data.target_epoch, previous_crosslink.epoch + MAX_CROSSLINK_EPOCHS)
+    assert data.crosslink.epoch == min(data.target_epoch, previous_crosslink.epoch + MAX_EPOCHS_PER_CROSSLINK)
     assert data.crosslink.previous_crosslink_root == hash_tree_root(previous_crosslink)
     assert data.crosslink.crosslink_data_root == ZERO_HASH  # [to be removed in phase 1]
     assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index d565266110..f386ee76e5 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -265,7 +265,7 @@ The `empty` function accepts and SSZ type as input and returns an object of that
 def get_custody_chunk_count(attestation: Attestation) -> int:
     crosslink_start_epoch = attestation.data.latest_crosslink.epoch
     crosslink_end_epoch = slot_to_epoch(attestation.data.slot)
-    crosslink_crosslink_length = min(MAX_CROSSLINK_EPOCHS, end_epoch - start_epoch)
+    crosslink_crosslink_length = min(MAX_EPOCHS_PER_CROSSLINK, end_epoch - start_epoch)
     chunks_per_epoch = 2 * BYTES_PER_SHARD_BLOCK * SLOTS_PER_EPOCH // BYTES_PER_CUSTODY_CHUNK
     return crosslink_crosslink_length * chunks_per_epoch
 ```
@@ -426,10 +426,10 @@ def process_early_derived_secret_reveal(state: BeaconState,
         # round key
         slash_validator(state, reveal.revealed_index, reveal.masker_index)
     else:
-        # Only a small penalty proportional to proposer slot reward for RANDAO reveal 
+        # Only a small penalty proportional to proposer slot reward for RANDAO reveal
         # that does not interfere with the custody period
-        # The penalty is proportional to the max proposer reward 
-        
+        # The penalty is proportional to the max proposer reward
+
         # Calculate penalty
         max_proposer_slot_reward = (
             get_base_reward(state, reveal.revealed_index) *
@@ -448,7 +448,7 @@ def process_early_derived_secret_reveal(state: BeaconState,
         increase_balance(state, whistleblower_index, whistleblowing_reward - proposer_reward)
         decrease_balance(state, reveal.revealed_index, penalty)
 
-        # Mark this derived secret as exposed so validator cannot be punished repeatedly 
+        # Mark this derived secret as exposed so validator cannot be punished repeatedly
         state.exposed_derived_secrets[reveal.epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS].append(reveal.revealed_index)
 
 ```
@@ -474,7 +474,7 @@ def process_chunk_challenge(state: BeaconState,
     # Verify the challenge is not a duplicate
     for record in state.custody_chunk_challenge_records:
         assert (
-            record.crosslink_data_root != challenge.attestation.data.crosslink_data_root or
+            record.crosslink_data_root != challenge.attestation.data.crosslink.crosslink_data_root or
             record.chunk_index != challenge.chunk_index
         )
     # Verify depth
@@ -486,7 +486,7 @@ def process_chunk_challenge(state: BeaconState,
         challenger_index=get_beacon_proposer_index(state),
         responder_index=challenge.responder_index
         deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE,
-        crosslink_data_root=challenge.attestation.data.crosslink_data_root,
+        crosslink_data_root=challenge.attestation.data.crosslink.crosslink_data_root,
         depth=depth,
         chunk_index=challenge.chunk_index,
     )
@@ -564,7 +564,7 @@ def process_bit_challenge(state: BeaconState,
         challenger_index=challenge.challenger_index,
         responder_index=challenge.responder_index,
         deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE,
-        crosslink_data_root=challenge.attestation.data.crosslink_data_root,
+        crosslink_data_root=challenge.attestation.data.crosslink.crosslink_data_root,
         chunk_count=chunk_count,
         chunk_bits_merkle_root=merkle_root(pad_to_power_of_2((challenge.chunk_bits))),
         responder_key=challenge.responder_key,
diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md
index 33ef8632b0..673a64a4a7 100644
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@@ -215,7 +215,7 @@ def get_shard_header(block: ShardBlock) -> ShardBlockHeader:
 def verify_shard_attestation_signature(state: BeaconState,
                                        attestation: ShardAttestation) -> None:
     data = attestation.data
-    persistent_committee = get_persistent_committee(state, data.shard, data.slot)
+    persistent_committee = get_persistent_committee(state, data.crosslink.shard, data.slot)
     assert verify_bitfield(attestation.aggregation_bitfield, len(persistent_committee))
     pubkeys = []
     for i, index in enumerate(persistent_committee):
@@ -225,7 +225,7 @@ def verify_shard_attestation_signature(state: BeaconState,
             pubkeys.append(validator.pubkey)
     assert bls_verify(
         pubkey=bls_aggregate_pubkeys(pubkeys),
-        message_hash=data.shard_block_root,
+        message_hash=data.crosslink.shard_block_root,
         signature=attestation.aggregate_signature,
         domain=get_domain(state, slot_to_epoch(data.slot), DOMAIN_SHARD_ATTESTER)
     )
@@ -312,7 +312,7 @@ def is_valid_shard_block(beacon_blocks: List[BeaconBlock],
     for _, attestation in enumerate(block.attestations):
         assert max(GENESIS_SHARD_SLOT, block.slot - SLOTS_PER_EPOCH) <= attestation.data.slot
         assert attestation.data.slot <= block.slot - MIN_ATTESTATION_INCLUSION_DELAY
-        assert attestation.data.shard == block.shard
+        assert attestation.data.crosslink.shard == block.shard
         verify_shard_attestation_signature(beacon_state, attestation)
 
     # Check signature
@@ -343,11 +343,11 @@ def is_valid_shard_attestation(valid_shard_blocks: List[ShardBlock],
     # Check shard block
     shard_block = next(
         block for block in valid_shard_blocks if
-        signing_root(block) == candidate.attestation.data.shard_block_root
+        signing_root(block) == candidate.attestation.data.crosslink.shard_block_root
     , None)
     assert shard_block != None
     assert shard_block.slot == attestation.data.slot
-    assert shard_block.shard == attestation.data.shard
+    assert shard_block.shard == attestation.data.crosslink.shard
 
     # Check signature
     verify_shard_attestation_signature(beacon_state, attestation)
@@ -382,18 +382,18 @@ def is_valid_beacon_attestation(shard: Shard,
     else:
         previous_attestation = next(
             attestation for attestation in valid_attestations if
-            attestation.data.crosslink_data_root == candidate.data.previous_crosslink.crosslink_data_root
+            attestation.data.crosslink.crosslink_data_root == candidate.data.previous_crosslink.crosslink_data_root
         , None)
         assert previous_attestation != None
         assert candidate.data.previous_attestation.epoch < slot_to_epoch(candidate.data.slot)
 
     # Check crosslink data root
     start_epoch = state.latest_crosslinks[shard].epoch
-    end_epoch = min(slot_to_epoch(candidate.data.slot) - CROSSLINK_LOOKBACK, start_epoch + MAX_CROSSLINK_EPOCHS)
+    end_epoch = min(slot_to_epoch(candidate.data.slot) - CROSSLINK_LOOKBACK, start_epoch + MAX_EPOCHS_PER_CROSSLINK)
     blocks = []
     for slot in range(start_epoch * SLOTS_PER_EPOCH, end_epoch * SLOTS_PER_EPOCH):
         blocks.append(shard_blocks[slot])
-    assert candidate.data.crosslink_data_root == compute_crosslink_data_root(blocks)
+    assert candidate.data.crosslink.crosslink_data_root == compute_crosslink_data_root(blocks)
 
     return True
 ```
diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index ca7f0eb3b3..61f80f68e2 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -271,7 +271,7 @@ _Note:_ This can be looked up in the state using:
 
 ##### Shard
 
-Set `attestation_data.shard = shard` where `shard` is the shard associated with the validator's committee defined by `get_crosslink_committees_at_slot`.
+Set `attestation_data.crosslink.shard = shard` where `shard` is the shard associated with the validator's committee defined by `get_crosslink_committees_at_slot`.
 
 ##### Previous crosslink root
 
@@ -279,7 +279,7 @@ Set `attestation_data.previous_crosslink_root = hash_tree_root(head_state.curren
 
 ##### Crosslink data root
 
-Set `attestation_data.crosslink_data_root = ZERO_HASH`.
+Set `attestation_data.crosslink.crosslink_data_root = ZERO_HASH`.
 
 _Note:_ This is a stub for phase 0.
 
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attestation.py b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
index bcf71376ce..24cafc2755 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@@ -113,7 +113,7 @@ def test_non_zero_crosslink_data_root(state):
     attestation = get_valid_attestation(state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.crosslink_data_root = b'\x42' * 32
+    attestation.data.crosslink.crosslink_data_root = b'\x42' * 32
 
     pre_state, post_state = run_attestation_processing(state, attestation, False)
 
@@ -126,7 +126,7 @@ def test_bad_previous_crosslink(state):
     for _ in range(spec.MIN_ATTESTATION_INCLUSION_DELAY):
         next_slot(state)
 
-    state.current_crosslinks[attestation.data.shard].epoch += 10
+    state.current_crosslinks[attestation.data.crosslink.shard].epoch += 10
 
     pre_state, post_state = run_attestation_processing(state, attestation, False)
 
diff --git a/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py b/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
index d6765e3a72..29e7347b12 100644
--- a/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
+++ b/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
@@ -64,7 +64,7 @@ def test_single_crosslink_update_from_current_epoch(state):
 
     pre_state, post_state = run_process_crosslinks(state)
 
-    shard = attestation.data.shard
+    shard = attestation.data.crosslink.shard
     assert post_state.previous_crosslinks[shard] != post_state.current_crosslinks[shard]
     assert pre_state.current_crosslinks[shard] != post_state.current_crosslinks[shard]
 
@@ -84,11 +84,11 @@ def test_single_crosslink_update_from_previous_epoch(state):
     pre_state, post_state = run_process_crosslinks(state)
     crosslink_deltas = get_crosslink_deltas(state)
 
-    shard = attestation.data.shard
+    shard = attestation.data.crosslink.shard
     assert post_state.previous_crosslinks[shard] != post_state.current_crosslinks[shard]
     assert pre_state.current_crosslinks[shard] != post_state.current_crosslinks[shard]
     # ensure rewarded
-    for index in get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.shard):
+    for index in get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.crosslink.shard):
         assert crosslink_deltas[0][index] > 0
         assert crosslink_deltas[1][index] == 0
 
@@ -108,7 +108,7 @@ def test_double_late_crosslink(state):
 
     for slot in range(spec.SLOTS_PER_EPOCH):
         attestation_2 = get_valid_attestation(state)
-        if attestation_2.data.shard == attestation_1.data.shard:
+        if attestation_2.data.crosslink.shard == attestation_1.data.crosslink.shard:
             break
         next_slot(state)
     fill_aggregate_attestation(state, attestation_2)
@@ -124,12 +124,12 @@ def test_double_late_crosslink(state):
     pre_state, post_state = run_process_crosslinks(state)
     crosslink_deltas = get_crosslink_deltas(state)
 
-    shard = attestation_2.data.shard
+    shard = attestation_2.data.crosslink.shard
 
     # ensure that the current crosslinks were not updated by the second attestation
     assert post_state.previous_crosslinks[shard] == post_state.current_crosslinks[shard]
     # ensure no reward, only penalties for the failed crosslink
-    for index in get_crosslink_committee(state, attestation_2.data.target_epoch, attestation_2.data.shard):
+    for index in get_crosslink_committee(state, attestation_2.data.target_epoch, attestation_2.data.crosslink.shard):
         assert crosslink_deltas[0][index] == 0
         assert crosslink_deltas[1][index] > 0
 
diff --git a/test_libs/pyspec/tests/helpers.py b/test_libs/pyspec/tests/helpers.py
index 3b9b6904d5..1ea299453d 100644
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@@ -10,6 +10,7 @@
 from eth2spec.phase0.spec import (
     # constants
     ZERO_HASH,
+    MAX_EPOCHS_PER_CROSSLINK,
     # SSZ
     Attestation,
     AttestationData,
@@ -17,6 +18,7 @@
     AttesterSlashing,
     BeaconBlock,
     BeaconBlockHeader,
+    Crosslink,
     Deposit,
     DepositData,
     Eth1Data,
@@ -174,14 +176,17 @@ def build_attestation_data(state, slot, shard):
 
     crosslinks = state.current_crosslinks if slot_to_epoch(slot) == get_current_epoch(state) else state.previous_crosslinks
     return AttestationData(
-        shard=shard,
         beacon_block_root=block_root,
         source_epoch=justified_epoch,
         source_root=justified_block_root,
         target_epoch=slot_to_epoch(slot),
         target_root=epoch_boundary_root,
-        crosslink_data_root=spec.ZERO_HASH,
-        previous_crosslink_root=hash_tree_root(crosslinks[shard]),
+        crosslink=Crosslink(
+            shard=shard,
+            epoch=min(slot_to_epoch(slot), crosslinks[shard].epoch + MAX_EPOCHS_PER_CROSSLINK),
+            crosslink_data_root=spec.ZERO_HASH,
+            previous_crosslink_root=hash_tree_root(crosslinks[shard]),
+        ),
     )
 
 
@@ -288,7 +293,7 @@ def get_valid_attestation(state, slot=None):
 
     attestation_data = build_attestation_data(state, slot, shard)
 
-    crosslink_committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.shard)
+    crosslink_committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.crosslink.shard)
 
     committee_size = len(crosslink_committee)
     bitfield_length = (committee_size + 7) // 8
@@ -381,7 +386,7 @@ def get_attestation_signature(state, attestation_data, privkey, custody_bit=0b0)
 
 
 def fill_aggregate_attestation(state, attestation):
-    crosslink_committee = get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.shard)
+    crosslink_committee = get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.crosslink.shard)
     for i in range(len(crosslink_committee)):
         attestation.aggregation_bitfield = set_bitfield_bit(attestation.aggregation_bitfield, i)
 

From b15105e1cbb4a597fea233b16eac23ae911570a6 Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Mon, 6 May 2019 17:34:03 +0100
Subject: [PATCH 3/8] Address Danny's comment

---
 specs/core/0_beacon-chain.md | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 156a2523d2..0bd85478ec 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1298,22 +1298,17 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
 
 ```python
 def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
-    shard_attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.crosslink.shard == shard]
-    candidate_crosslinks = [
-        c for c in [a.data.crosslink for a in shard_attestations]
-        if hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c))
-    ]
-    if len(candidate_crosslinks) == 0:
-        return Crosslink(), []
-
-    def get_attestations_for(crosslink: Crosslink) -> List[PendingAttestation]:
-        return [a for a in shard_attestations if a.data.crosslink == crosslink]
-    # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
-    winning_crosslink = max(candidate_crosslinks, key=lambda crosslink: (
-        get_attesting_balance(state, get_attestations_for(crosslink)), crosslink.crosslink_data_root
+    attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.crosslink.shard == shard]
+    crosslinks = list(filter(
+        lambda c: hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c)),
+        [a.data.crosslink for a in attestations]
     ))
-
-    return winning_crosslink, get_unslashed_attesting_indices(state, get_attestations_for(winning_crosslink))
+    # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
+    winning_crosslink = max(crosslinks, key=lambda c: (
+        get_attesting_balance(state, [a for a in attestations if a.data.crosslink == c]), c.crosslink_data_root
+    ), default=Crosslink())
+    winning_attestations = [a for a in attestations if a.data.crosslink == winning_crosslink]
+    return winning_crosslink, get_unslashed_attesting_indices(state, winning_attestations)
 ```
 
 #### Justification and finalization

From 8b1a2edb7c650e0e0205e11c44f44a2a578ce392 Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Mon, 6 May 2019 17:53:49 +0100
Subject: [PATCH 4/8] Fix genesis bug

---
 specs/core/0_beacon-chain.md | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 9aed2001a8..04ab38e18f 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -767,7 +767,7 @@ def get_epoch_start_shard(state: BeaconState, epoch: Epoch) -> Shard:
 ```python
 def get_attestation_data_slot(state: BeaconState, data: AttestationData) -> Slot:
     committee_count = get_epoch_committee_count(state, data.target_epoch)
-    offset = (data.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target_epoch)) % SHARD_COUNT
+    offset = (data.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target_epoch)) % SHARD_COUNT
     return get_epoch_start_slot(data.target_epoch) + offset // (committee_count // SLOTS_PER_EPOCH)
 ```
 
@@ -1705,14 +1705,14 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     )
 
     assert data.target_epoch in (get_previous_epoch(state), get_current_epoch(state))
-    if data.target_epoch == get_previous_epoch(state):
-        ffg_data = (state.previous_justified_epoch, state.previous_justified_root, get_previous_epoch(state))
-        previous_crosslink = state.previous_crosslinks[data.crosslink.shard]
-        state.previous_epoch_attestations.append(pending_attestation)
     if data.target_epoch == get_current_epoch(state):
         ffg_data = (state.current_justified_epoch, state.current_justified_root, get_current_epoch(state))
         previous_crosslink = state.current_crosslinks[data.crosslink.shard]
         state.current_epoch_attestations.append(pending_attestation)
+    else:
+        ffg_data = (state.previous_justified_epoch, state.previous_justified_root, get_previous_epoch(state))
+        previous_crosslink = state.previous_crosslinks[data.crosslink.shard]
+        state.previous_epoch_attestations.append(pending_attestation)
 
     # Check FFG data, crosslink data, and signature
     assert ffg_data == (data.source_epoch, data.source_root, data.target_epoch)

From f4db9ebae00338ba336943a08271012099bcef1d Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Mon, 6 May 2019 18:26:14 +0100
Subject: [PATCH 5/8] Renamings triggered by HW comment

---
 specs/core/0_beacon-chain.md                  | 26 +++++++++----------
 specs/core/0_fork-choice.md                   |  2 +-
 specs/core/1_custody-game.md                  | 14 +++++-----
 specs/core/1_shard-data-chains.md             | 16 ++++++------
 specs/validator/0_beacon-chain-validator.md   |  6 ++---
 .../test_process_attestation.py               |  2 +-
 .../test_process_block_header.py              |  4 +--
 test_libs/pyspec/tests/helpers.py             | 12 ++++-----
 test_libs/pyspec/tests/test_sanity.py         |  6 ++---
 9 files changed, 44 insertions(+), 44 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 04ab38e18f..afca9eb1ba 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -287,9 +287,9 @@ The types are defined topologically to aid in facilitating an executable version
     # Epoch number
     'epoch': 'uint64',
     # Root of the previous crosslink
-    'previous_crosslink_root': 'bytes32',
+    'parent_crosslink_root': 'bytes32',
     # Root of the crosslinked shard data since the previous crosslink
-    'crosslink_data_root': 'bytes32',
+    'data_root': 'bytes32',
 }
 ```
 
@@ -369,7 +369,7 @@ The types are defined topologically to aid in facilitating an executable version
 ```python
 {
     'slot': 'uint64',
-    'previous_block_root': 'bytes32',
+    'parent_block_root': 'bytes32',
     'state_root': 'bytes32',
     'block_body_root': 'bytes32',
     'signature': 'bytes96',
@@ -536,7 +536,7 @@ The types are defined topologically to aid in facilitating an executable version
 {
     # Header
     'slot': 'uint64',
-    'previous_block_root': 'bytes32',
+    'parent_block_root': 'bytes32',
     'state_root': 'bytes32',
     'body': BeaconBlockBody,
     'signature': 'bytes96',
@@ -1306,12 +1306,12 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
 def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
     attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.crosslink.shard == shard]
     crosslinks = list(filter(
-        lambda c: hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c)),
+        lambda c: hash_tree_root(state.current_crosslinks[shard]) in (c.parent_crosslink_root, hash_tree_root(c)),
         [a.data.crosslink for a in attestations]
     ))
     # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
     winning_crosslink = max(crosslinks, key=lambda c: (
-        get_attesting_balance(state, [a for a in attestations if a.data.crosslink == c]), c.crosslink_data_root
+        get_attesting_balance(state, [a for a in attestations if a.data.crosslink == c]), c.data_root
     ), default=Crosslink())
     winning_attestations = [a for a in attestations if a.data.crosslink == winning_crosslink]
     return winning_crosslink, get_unslashed_attesting_indices(state, winning_attestations)
@@ -1586,11 +1586,11 @@ def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
     # Verify that the slots match
     assert block.slot == state.slot
     # Verify that the parent matches
-    assert block.previous_block_root == signing_root(state.latest_block_header)
+    assert block.parent_block_root == signing_root(state.latest_block_header)
     # Save current block as the new latest block
     state.latest_block_header = BeaconBlockHeader(
         slot=block.slot,
-        previous_block_root=block.previous_block_root,
+        parent_block_root=block.parent_block_root,
         block_body_root=hash_tree_root(block.body),
     )
     # Verify proposer is not slashed
@@ -1707,18 +1707,18 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     assert data.target_epoch in (get_previous_epoch(state), get_current_epoch(state))
     if data.target_epoch == get_current_epoch(state):
         ffg_data = (state.current_justified_epoch, state.current_justified_root, get_current_epoch(state))
-        previous_crosslink = state.current_crosslinks[data.crosslink.shard]
+        parent_crosslink = state.current_crosslinks[data.crosslink.shard]
         state.current_epoch_attestations.append(pending_attestation)
     else:
         ffg_data = (state.previous_justified_epoch, state.previous_justified_root, get_previous_epoch(state))
-        previous_crosslink = state.previous_crosslinks[data.crosslink.shard]
+        parent_crosslink = state.previous_crosslinks[data.crosslink.shard]
         state.previous_epoch_attestations.append(pending_attestation)
 
     # Check FFG data, crosslink data, and signature
     assert ffg_data == (data.source_epoch, data.source_root, data.target_epoch)
-    assert data.crosslink.epoch == min(data.target_epoch, previous_crosslink.epoch + MAX_EPOCHS_PER_CROSSLINK)
-    assert data.crosslink.previous_crosslink_root == hash_tree_root(previous_crosslink)
-    assert data.crosslink.crosslink_data_root == ZERO_HASH  # [to be removed in phase 1]
+    assert data.crosslink.epoch == min(data.target_epoch, parent_crosslink.epoch + MAX_EPOCHS_PER_CROSSLINK)
+    assert data.crosslink.parent_crosslink_root == hash_tree_root(parent_crosslink)
+    assert data.crosslink.data_root == ZERO_HASH  # [to be removed in phase 1]
     assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
 ```
 
diff --git a/specs/core/0_fork-choice.md b/specs/core/0_fork-choice.md
index 549e9e2077..891120de8e 100644
--- a/specs/core/0_fork-choice.md
+++ b/specs/core/0_fork-choice.md
@@ -38,7 +38,7 @@ All terminology, constants, functions, and protocol mechanics defined in the [Ph
 
 Processing the beacon chain is similar to processing the Ethereum 1.0 chain. Clients download and process blocks and maintain a view of what is the current "canonical chain", terminating at the current "head". For a beacon block, `block`, to be processed by a node, the following conditions must be met:
 
-* The parent block with root `block.previous_block_root` has been processed and accepted.
+* The parent block with root `block.parent_block_root` has been processed and accepted.
 * An Ethereum 1.0 block pointed to by the `state.latest_eth1_data.block_hash` has been processed and accepted.
 * The node's Unix time is greater than or equal to `state.genesis_time + block.slot * SECONDS_PER_SLOT`.
 
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index e259b82a55..a030c577bf 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -147,7 +147,7 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
     'challenger_index': ValidatorIndex,
     'responder_index': ValidatorIndex,
     'deadline': Epoch,
-    'crosslink_data_root': Hash,
+    'data_root': Hash,
     'depth': 'uint64',
     'chunk_index': 'uint64',
 }
@@ -161,7 +161,7 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
     'challenger_index': ValidatorIndex,
     'responder_index': ValidatorIndex,
     'deadline': Epoch,
-    'crosslink_data_root': Hash,
+    'data_root': Hash,
     'chunk_count': 'uint64',
     'chunk_bits_merkle_root': Hash,
     'responder_key': BLSSignature,
@@ -474,7 +474,7 @@ def process_chunk_challenge(state: BeaconState,
     # Verify the challenge is not a duplicate
     for record in state.custody_chunk_challenge_records:
         assert (
-            record.crosslink_data_root != challenge.attestation.data.crosslink.crosslink_data_root or
+            record.data_root != challenge.attestation.data.crosslink.data_root or
             record.chunk_index != challenge.chunk_index
         )
     # Verify depth
@@ -486,7 +486,7 @@ def process_chunk_challenge(state: BeaconState,
         challenger_index=get_beacon_proposer_index(state),
         responder_index=challenge.responder_index
         deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE,
-        crosslink_data_root=challenge.attestation.data.crosslink.crosslink_data_root,
+        data_root=challenge.attestation.data.crosslink.data_root,
         depth=depth,
         chunk_index=challenge.chunk_index,
     )
@@ -564,7 +564,7 @@ def process_bit_challenge(state: BeaconState,
         challenger_index=challenge.challenger_index,
         responder_index=challenge.responder_index,
         deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE,
-        crosslink_data_root=challenge.attestation.data.crosslink.crosslink_data_root,
+        data_root=challenge.attestation.data.crosslink.data_root,
         chunk_count=chunk_count,
         chunk_bits_merkle_root=merkle_root(pad_to_power_of_2((challenge.chunk_bits))),
         responder_key=challenge.responder_key,
@@ -610,7 +610,7 @@ def process_chunk_challenge_response(state: BeaconState,
         branch=response.data_branch,
         depth=challenge.depth,
         index=response.chunk_index,
-        root=challenge.crosslink_data_root,
+        root=challenge.data_root,
     )
     # Clear the challenge
     records = state.custody_chunk_challenge_records
@@ -632,7 +632,7 @@ def process_bit_challenge_response(state: BeaconState,
         branch=response.data_branch,
         depth=math.log2(next_power_of_two(challenge.chunk_count)),
         index=response.chunk_index,
-        root=challenge.crosslink_data_root,
+        root=challenge.data_root,
     )
     # Verify the chunk bit leaf matches the challenge data
     assert verify_merkle_branch(
diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md
index 9fbc696929..316bd0068f 100644
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@@ -78,7 +78,7 @@ This document describes the shard data layer and the shard fork choice rule in P
     'slot': Slot,
     'shard': Shard,
     'beacon_chain_root': Hash,
-    'previous_block_root': Hash,
+    'parent_block_root': Hash,
     'data': ShardBlockBody,
     'state_root': Hash,
     'attestations': [ShardAttestation],
@@ -93,7 +93,7 @@ This document describes the shard data layer and the shard fork choice rule in P
     'slot': Slot,
     'shard': Shard,
     'beacon_chain_root': Hash,
-    'previous_block_root': Hash,
+    'parent_block_root': Hash,
     'body_root': Hash,
     'state_root': Hash,
     'attestations': [ShardAttestation],
@@ -201,7 +201,7 @@ def get_shard_header(block: ShardBlock) -> ShardBlockHeader:
         slot: block.slot,
         shard: block.shard,
         beacon_chain_root: block.beacon_chain_root,
-        previous_block_root: block.previous_block_root,
+        parent_block_root: block.parent_block_root,
         body_root: hash_tree_root(block.body),
         state_root: block.state_root,
         attestations: block.attestations,
@@ -296,11 +296,11 @@ def is_valid_shard_block(beacon_blocks: List[BeaconBlock],
 
     # Check parent block
     if block.slot == PHASE_1_GENESIS_SLOT:
-        assert candidate.previous_block_root == ZERO_HASH
+        assert candidate.parent_block_root == ZERO_HASH
     else:
         parent_block = next(
             block for block in valid_shard_blocks if
-            signing_root(block) == candidate.previous_block_root
+            signing_root(block) == candidate.parent_block_root
         , None)
         assert parent_block != None
         assert parent_block.shard == block.shard
@@ -378,11 +378,11 @@ def is_valid_beacon_attestation(shard: Shard,
 
     # Check previous attestation
     if candidate.data.previous_crosslink.epoch <= PHASE_1_GENESIS_EPOCH:
-        assert candidate.data.previous_crosslink.crosslink_data_root == ZERO_HASH
+        assert candidate.data.previous_crosslink.data_root == ZERO_HASH
     else:
         previous_attestation = next(
             attestation for attestation in valid_attestations if
-            attestation.data.crosslink.crosslink_data_root == candidate.data.previous_crosslink.crosslink_data_root
+            attestation.data.crosslink.data_root == candidate.data.previous_crosslink.data_root
         , None)
         assert previous_attestation != None
         assert candidate.data.previous_attestation.epoch < slot_to_epoch(candidate.data.slot)
@@ -393,7 +393,7 @@ def is_valid_beacon_attestation(shard: Shard,
     blocks = []
     for slot in range(start_epoch * SLOTS_PER_EPOCH, end_epoch * SLOTS_PER_EPOCH):
         blocks.append(shard_blocks[slot])
-    assert candidate.data.crosslink.crosslink_data_root == compute_crosslink_data_root(blocks)
+    assert candidate.data.crosslink.data_root == compute_crosslink_data_root(blocks)
 
     return True
 ```
diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index cfe6a8f1ff..dae9ac85f4 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -152,7 +152,7 @@ Set `block.slot = slot` where `slot` is the current slot at which the validator
 
 ##### Parent root
 
-Set `block.previous_block_root = signing_root(parent)`.
+Set `block.parent_block_root = signing_root(parent)`.
 
 ##### State root
 
@@ -275,11 +275,11 @@ Set `attestation_data.crosslink.shard = shard` where `shard` is the shard associ
 
 ##### Previous crosslink root
 
-Set `attestation_data.previous_crosslink_root = hash_tree_root(head_state.current_crosslinks[shard])`.
+Set `attestation_data.parent_crosslink_root = hash_tree_root(head_state.current_crosslinks[shard])`.
 
 ##### Crosslink data root
 
-Set `attestation_data.crosslink.crosslink_data_root = ZERO_HASH`.
+Set `attestation_data.crosslink.data_root = ZERO_HASH`.
 
 *Note*: This is a stub for Phase 0.
 
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attestation.py b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
index 24cafc2755..fcbc68fe9b 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@@ -113,7 +113,7 @@ def test_non_zero_crosslink_data_root(state):
     attestation = get_valid_attestation(state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.crosslink.crosslink_data_root = b'\x42' * 32
+    attestation.data.crosslink.data_root = b'\x42' * 32
 
     pre_state, post_state = run_attestation_processing(state, attestation, False)
 
diff --git a/test_libs/pyspec/tests/block_processing/test_process_block_header.py b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
index b35b0a9c11..e4fa516b1e 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_block_header.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
@@ -53,9 +53,9 @@ def test_invalid_slot(state):
     return pre_state, block, None
 
 
-def test_invalid_previous_block_root(state):
+def test_invalid_parent_block_root(state):
     block = build_empty_block_for_next_slot(state)
-    block.previous_block_root = b'\12' * 32  # invalid prev root
+    block.parent_block_root = b'\12' * 32  # invalid prev root
 
     pre_state, post_state = run_block_header_processing(state, block, valid=False)
     return pre_state, block, None
diff --git a/test_libs/pyspec/tests/helpers.py b/test_libs/pyspec/tests/helpers.py
index 1ea299453d..e7ee826db4 100644
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@@ -128,7 +128,7 @@ def build_empty_block_for_next_slot(state):
     previous_block_header = deepcopy(state.latest_block_header)
     if previous_block_header.state_root == spec.ZERO_HASH:
         previous_block_header.state_root = state.hash_tree_root()
-    empty_block.previous_block_root = signing_root(previous_block_header)
+    empty_block.parent_block_root = signing_root(previous_block_header)
     return empty_block
 
 
@@ -155,7 +155,7 @@ def build_attestation_data(state, slot, shard):
     assert state.slot >= slot
 
     if slot == state.slot:
-        block_root = build_empty_block_for_next_slot(state).previous_block_root
+        block_root = build_empty_block_for_next_slot(state).parent_block_root
     else:
         block_root = get_block_root_at_slot(state, slot)
 
@@ -184,8 +184,8 @@ def build_attestation_data(state, slot, shard):
         crosslink=Crosslink(
             shard=shard,
             epoch=min(slot_to_epoch(slot), crosslinks[shard].epoch + MAX_EPOCHS_PER_CROSSLINK),
-            crosslink_data_root=spec.ZERO_HASH,
-            previous_crosslink_root=hash_tree_root(crosslinks[shard]),
+            data_root=spec.ZERO_HASH,
+            parent_crosslink_root=hash_tree_root(crosslinks[shard]),
         ),
     )
 
@@ -240,12 +240,12 @@ def get_valid_proposer_slashing(state):
 
     header_1 = BeaconBlockHeader(
         slot=slot,
-        previous_block_root=ZERO_HASH,
+        parent_block_root=ZERO_HASH,
         state_root=ZERO_HASH,
         block_body_root=ZERO_HASH,
     )
     header_2 = deepcopy(header_1)
-    header_2.previous_block_root = b'\x02' * 32
+    header_2.parent_block_root = b'\x02' * 32
     header_2.slot = slot + 1
 
     domain = get_domain(
diff --git a/test_libs/pyspec/tests/test_sanity.py b/test_libs/pyspec/tests/test_sanity.py
index 1b4d20f4c5..83ba9cc113 100644
--- a/test_libs/pyspec/tests/test_sanity.py
+++ b/test_libs/pyspec/tests/test_sanity.py
@@ -68,7 +68,7 @@ def test_empty_block_transition(state):
     state_transition(test_state, block)
 
     assert len(test_state.eth1_data_votes) == len(state.eth1_data_votes) + 1
-    assert get_block_root_at_slot(test_state, state.slot) == block.previous_block_root
+    assert get_block_root_at_slot(test_state, state.slot) == block.parent_block_root
 
     return state, [block], test_state
 
@@ -82,7 +82,7 @@ def test_skipped_slots(state):
 
     assert test_state.slot == block.slot
     for slot in range(state.slot, test_state.slot):
-        assert get_block_root_at_slot(test_state, slot) == block.previous_block_root
+        assert get_block_root_at_slot(test_state, slot) == block.parent_block_root
 
     return state, [block], test_state
 
@@ -96,7 +96,7 @@ def test_empty_epoch_transition(state):
 
     assert test_state.slot == block.slot
     for slot in range(state.slot, test_state.slot):
-        assert get_block_root_at_slot(test_state, slot) == block.previous_block_root
+        assert get_block_root_at_slot(test_state, slot) == block.parent_block_root
 
     return state, [block], test_state
 

From ea60fb632c3a07d2dae29b6ca8d37cea204bc6e7 Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Mon, 6 May 2019 20:49:46 +0100
Subject: [PATCH 6/8] More renaming

---
 specs/core/0_beacon-chain.md                       | 14 +++++++-------
 specs/core/0_fork-choice.md                        |  2 +-
 specs/core/1_shard-data-chains.md                  | 10 +++++-----
 specs/validator/0_beacon-chain-validator.md        |  4 ++--
 .../block_processing/test_process_block_header.py  |  2 +-
 test_libs/pyspec/tests/helpers.py                  | 12 ++++++------
 test_libs/pyspec/tests/test_sanity.py              |  6 +++---
 7 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index afca9eb1ba..ccba4c817d 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -287,7 +287,7 @@ The types are defined topologically to aid in facilitating an executable version
     # Epoch number
     'epoch': 'uint64',
     # Root of the previous crosslink
-    'parent_crosslink_root': 'bytes32',
+    'parent_root': 'bytes32',
     # Root of the crosslinked shard data since the previous crosslink
     'data_root': 'bytes32',
 }
@@ -369,7 +369,7 @@ The types are defined topologically to aid in facilitating an executable version
 ```python
 {
     'slot': 'uint64',
-    'parent_block_root': 'bytes32',
+    'parent_root': 'bytes32',
     'state_root': 'bytes32',
     'block_body_root': 'bytes32',
     'signature': 'bytes96',
@@ -536,7 +536,7 @@ The types are defined topologically to aid in facilitating an executable version
 {
     # Header
     'slot': 'uint64',
-    'parent_block_root': 'bytes32',
+    'parent_root': 'bytes32',
     'state_root': 'bytes32',
     'body': BeaconBlockBody,
     'signature': 'bytes96',
@@ -1306,7 +1306,7 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
 def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
     attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.crosslink.shard == shard]
     crosslinks = list(filter(
-        lambda c: hash_tree_root(state.current_crosslinks[shard]) in (c.parent_crosslink_root, hash_tree_root(c)),
+        lambda c: hash_tree_root(state.current_crosslinks[shard]) in (c.parent_root, hash_tree_root(c)),
         [a.data.crosslink for a in attestations]
     ))
     # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
@@ -1586,11 +1586,11 @@ def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
     # Verify that the slots match
     assert block.slot == state.slot
     # Verify that the parent matches
-    assert block.parent_block_root == signing_root(state.latest_block_header)
+    assert block.parent_root == signing_root(state.latest_block_header)
     # Save current block as the new latest block
     state.latest_block_header = BeaconBlockHeader(
         slot=block.slot,
-        parent_block_root=block.parent_block_root,
+        parent_root=block.parent_root,
         block_body_root=hash_tree_root(block.body),
     )
     # Verify proposer is not slashed
@@ -1717,7 +1717,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     # Check FFG data, crosslink data, and signature
     assert ffg_data == (data.source_epoch, data.source_root, data.target_epoch)
     assert data.crosslink.epoch == min(data.target_epoch, parent_crosslink.epoch + MAX_EPOCHS_PER_CROSSLINK)
-    assert data.crosslink.parent_crosslink_root == hash_tree_root(parent_crosslink)
+    assert data.crosslink.parent_root == hash_tree_root(parent_crosslink)
     assert data.crosslink.data_root == ZERO_HASH  # [to be removed in phase 1]
     assert verify_indexed_attestation(state, convert_to_indexed(state, attestation))
 ```
diff --git a/specs/core/0_fork-choice.md b/specs/core/0_fork-choice.md
index 891120de8e..91c3e27ee4 100644
--- a/specs/core/0_fork-choice.md
+++ b/specs/core/0_fork-choice.md
@@ -38,7 +38,7 @@ All terminology, constants, functions, and protocol mechanics defined in the [Ph
 
 Processing the beacon chain is similar to processing the Ethereum 1.0 chain. Clients download and process blocks and maintain a view of what is the current "canonical chain", terminating at the current "head". For a beacon block, `block`, to be processed by a node, the following conditions must be met:
 
-* The parent block with root `block.parent_block_root` has been processed and accepted.
+* The parent block with root `block.parent_root` has been processed and accepted.
 * An Ethereum 1.0 block pointed to by the `state.latest_eth1_data.block_hash` has been processed and accepted.
 * The node's Unix time is greater than or equal to `state.genesis_time + block.slot * SECONDS_PER_SLOT`.
 
diff --git a/specs/core/1_shard-data-chains.md b/specs/core/1_shard-data-chains.md
index 316bd0068f..ca59c3ebc4 100644
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@@ -78,7 +78,7 @@ This document describes the shard data layer and the shard fork choice rule in P
     'slot': Slot,
     'shard': Shard,
     'beacon_chain_root': Hash,
-    'parent_block_root': Hash,
+    'parent_root': Hash,
     'data': ShardBlockBody,
     'state_root': Hash,
     'attestations': [ShardAttestation],
@@ -93,7 +93,7 @@ This document describes the shard data layer and the shard fork choice rule in P
     'slot': Slot,
     'shard': Shard,
     'beacon_chain_root': Hash,
-    'parent_block_root': Hash,
+    'parent_root': Hash,
     'body_root': Hash,
     'state_root': Hash,
     'attestations': [ShardAttestation],
@@ -201,7 +201,7 @@ def get_shard_header(block: ShardBlock) -> ShardBlockHeader:
         slot: block.slot,
         shard: block.shard,
         beacon_chain_root: block.beacon_chain_root,
-        parent_block_root: block.parent_block_root,
+        parent_root: block.parent_root,
         body_root: hash_tree_root(block.body),
         state_root: block.state_root,
         attestations: block.attestations,
@@ -296,11 +296,11 @@ def is_valid_shard_block(beacon_blocks: List[BeaconBlock],
 
     # Check parent block
     if block.slot == PHASE_1_GENESIS_SLOT:
-        assert candidate.parent_block_root == ZERO_HASH
+        assert candidate.parent_root == ZERO_HASH
     else:
         parent_block = next(
             block for block in valid_shard_blocks if
-            signing_root(block) == candidate.parent_block_root
+            signing_root(block) == candidate.parent_root
         , None)
         assert parent_block != None
         assert parent_block.shard == block.shard
diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index dae9ac85f4..a0173ebe92 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -152,7 +152,7 @@ Set `block.slot = slot` where `slot` is the current slot at which the validator
 
 ##### Parent root
 
-Set `block.parent_block_root = signing_root(parent)`.
+Set `block.parent_root = signing_root(parent)`.
 
 ##### State root
 
@@ -275,7 +275,7 @@ Set `attestation_data.crosslink.shard = shard` where `shard` is the shard associ
 
 ##### Previous crosslink root
 
-Set `attestation_data.parent_crosslink_root = hash_tree_root(head_state.current_crosslinks[shard])`.
+Set `attestation_data.parent_root = hash_tree_root(head_state.current_crosslinks[shard])`.
 
 ##### Crosslink data root
 
diff --git a/test_libs/pyspec/tests/block_processing/test_process_block_header.py b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
index e4fa516b1e..36c7298210 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_block_header.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
@@ -55,7 +55,7 @@ def test_invalid_slot(state):
 
 def test_invalid_parent_block_root(state):
     block = build_empty_block_for_next_slot(state)
-    block.parent_block_root = b'\12' * 32  # invalid prev root
+    block.parent_root = b'\12' * 32  # invalid prev root
 
     pre_state, post_state = run_block_header_processing(state, block, valid=False)
     return pre_state, block, None
diff --git a/test_libs/pyspec/tests/helpers.py b/test_libs/pyspec/tests/helpers.py
index e7ee826db4..2024885763 100644
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@@ -128,7 +128,7 @@ def build_empty_block_for_next_slot(state):
     previous_block_header = deepcopy(state.latest_block_header)
     if previous_block_header.state_root == spec.ZERO_HASH:
         previous_block_header.state_root = state.hash_tree_root()
-    empty_block.parent_block_root = signing_root(previous_block_header)
+    empty_block.parent_root = signing_root(previous_block_header)
     return empty_block
 
 
@@ -155,7 +155,7 @@ def build_attestation_data(state, slot, shard):
     assert state.slot >= slot
 
     if slot == state.slot:
-        block_root = build_empty_block_for_next_slot(state).parent_block_root
+        block_root = build_empty_block_for_next_slot(state).parent_root
     else:
         block_root = get_block_root_at_slot(state, slot)
 
@@ -185,7 +185,7 @@ def build_attestation_data(state, slot, shard):
             shard=shard,
             epoch=min(slot_to_epoch(slot), crosslinks[shard].epoch + MAX_EPOCHS_PER_CROSSLINK),
             data_root=spec.ZERO_HASH,
-            parent_crosslink_root=hash_tree_root(crosslinks[shard]),
+            parent_root=hash_tree_root(crosslinks[shard]),
         ),
     )
 
@@ -240,12 +240,12 @@ def get_valid_proposer_slashing(state):
 
     header_1 = BeaconBlockHeader(
         slot=slot,
-        parent_block_root=ZERO_HASH,
+        parent_root=ZERO_HASH,
         state_root=ZERO_HASH,
-        block_body_root=ZERO_HASH,
+        body_root=ZERO_HASH,
     )
     header_2 = deepcopy(header_1)
-    header_2.parent_block_root = b'\x02' * 32
+    header_2.parent_root = b'\x02' * 32
     header_2.slot = slot + 1
 
     domain = get_domain(
diff --git a/test_libs/pyspec/tests/test_sanity.py b/test_libs/pyspec/tests/test_sanity.py
index 83ba9cc113..0cb1b9be3b 100644
--- a/test_libs/pyspec/tests/test_sanity.py
+++ b/test_libs/pyspec/tests/test_sanity.py
@@ -68,7 +68,7 @@ def test_empty_block_transition(state):
     state_transition(test_state, block)
 
     assert len(test_state.eth1_data_votes) == len(state.eth1_data_votes) + 1
-    assert get_block_root_at_slot(test_state, state.slot) == block.parent_block_root
+    assert get_block_root_at_slot(test_state, state.slot) == block.parent_root
 
     return state, [block], test_state
 
@@ -82,7 +82,7 @@ def test_skipped_slots(state):
 
     assert test_state.slot == block.slot
     for slot in range(state.slot, test_state.slot):
-        assert get_block_root_at_slot(test_state, slot) == block.parent_block_root
+        assert get_block_root_at_slot(test_state, slot) == block.parent_root
 
     return state, [block], test_state
 
@@ -96,7 +96,7 @@ def test_empty_epoch_transition(state):
 
     assert test_state.slot == block.slot
     for slot in range(state.slot, test_state.slot):
-        assert get_block_root_at_slot(test_state, slot) == block.parent_block_root
+        assert get_block_root_at_slot(test_state, slot) == block.parent_root
 
     return state, [block], test_state
 

From 964e55cd4a8b8bfecbd70e279c13e69c6c977e22 Mon Sep 17 00:00:00 2001
From: Justin Drake <drakefjustin@gmail.com>
Date: Tue, 7 May 2019 08:52:56 +0100
Subject: [PATCH 7/8] block_body_root => body_root

---
 specs/core/0_beacon-chain.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index ccba4c817d..9f80fe1736 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -371,7 +371,7 @@ The types are defined topologically to aid in facilitating an executable version
     'slot': 'uint64',
     'parent_root': 'bytes32',
     'state_root': 'bytes32',
-    'block_body_root': 'bytes32',
+    'body_root': 'bytes32',
     'signature': 'bytes96',
 }
 ```
@@ -1591,7 +1591,7 @@ def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
     state.latest_block_header = BeaconBlockHeader(
         slot=block.slot,
         parent_root=block.parent_root,
-        block_body_root=hash_tree_root(block.body),
+        body_root=hash_tree_root(block.body),
     )
     # Verify proposer is not slashed
     proposer = state.validator_registry[get_beacon_proposer_index(state)]

From 13d2ee696939e192534c0278eb271fe53510caf7 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Tue, 7 May 2019 11:49:45 -0600
Subject: [PATCH 8/8] cleanup validator guide for crosslinks

---
 specs/validator/0_beacon-chain-validator.md | 53 +++++++--------------
 1 file changed, 17 insertions(+), 36 deletions(-)

diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index a0173ebe92..a95052b860 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -37,14 +37,9 @@
                 - [Voluntary exits](#voluntary-exits)
         - [Attestations](#attestations-1)
             - [Attestation data](#attestation-data)
-                - [Slot](#slot-1)
-                - [Beacon block root](#beacon-block-root)
-                - [Source epoch](#source-epoch)
-                - [Source root](#source-root)
-                - [Target root](#target-root)
-                - [Shard](#shard)
-                - [Previous crosslink root](#previous-crosslink-root)
-                - [Crosslink data root](#crosslink-data-root)
+                - [LMD GHOST vote](#lmd-ghost-vote)
+                - [FFG vote](#ffg-vote)
+                - [Crosslink vote](#crosslink-vote)
             - [Construct attestation](#construct-attestation)
                 - [Data](#data)
                 - [Aggregation bitfield](#aggregation-bitfield)
@@ -245,43 +240,29 @@ First the validator should construct `attestation_data`, an [`AttestationData`](
 * Let `head_block` be the result of running the fork choice during the assigned slot.
 * Let `head_state` be the state of `head_block` processed through any empty slots up to the assigned slot.
 
-##### Slot
-
-Set `attestation_data.slot = head_state.slot`.
-
-##### Beacon block root
+##### LMD GHOST vote
 
 Set `attestation_data.beacon_block_root = signing_root(head_block)`.
 
-##### Source epoch
-
-Set `attestation_data.source_epoch = head_state.justified_epoch`.
-
-##### Source root
-
-Set `attestation_data.source_root = head_state.current_justified_root`.
+##### FFG vote
 
-##### Target root
+* Set `attestation_data.source_epoch = head_state.justified_epoch`.
+* Set `attestation_data.source_root = head_state.current_justified_root`.
+* Set `attestation_data.target_epoch = get_current_epoch(head_state)`
+* Set `attestation_data.target_root = signing_root(epoch_boundary_block)` where `epoch_boundary_block` is the block at the most recent epoch boundary.
 
-Set `attestation_data.target_root = signing_root(epoch_boundary)` where `epoch_boundary` is the block at the most recent epoch boundary.
-
-*Note*: This can be looked up in the state using:
+*Note*: `epoch_boundary_block` can be looked up in the state using:
 * Let `epoch_start_slot = get_epoch_start_slot(get_current_epoch(head_state))`.
-* Set `epoch_boundary = head if epoch_start_slot == head_state.slot else get_block_root(state, epoch_start_slot)`.
-
-##### Shard
-
-Set `attestation_data.crosslink.shard = shard` where `shard` is the shard associated with the validator's committee defined by `get_crosslink_committees_at_slot`.
+* Let `epoch_boundary_block = head if epoch_start_slot == head_state.slot else get_block_root(state, epoch_start_slot)`.
 
-##### Previous crosslink root
+##### Crosslink vote
 
-Set `attestation_data.parent_root = hash_tree_root(head_state.current_crosslinks[shard])`.
+Construct `attestation_data.crosslink` via the following
 
-##### Crosslink data root
-
-Set `attestation_data.crosslink.data_root = ZERO_HASH`.
-
-*Note*: This is a stub for Phase 0.
+* Set `attestation_data.crosslink.shard = shard` where `shard` is the shard associated with the validator's committee defined by `get_crosslink_committees_at_slot`.
+* Set `attestation_data.crosslink.epoch = min(attestation_data.target_epoch, head_state.current_crosslinks[shard].epoch + MAX_EPOCHS_PER_CROSSLINK)`.
+* Set `attestation_data.crosslink.parent_root = hash_tree_root(head_state.current_crosslinks[shard])`.
+* Set `attestation_data.crosslink.data_root = ZERO_HASH`. *Note*: This is a stub for Phase 0.
 
 #### Construct attestation