diff --git a/configs/constant_presets/mainnet.yaml b/configs/constant_presets/mainnet.yaml
index 2aa45cde3..f9acf5bf7 100644
--- a/configs/constant_presets/mainnet.yaml
+++ b/configs/constant_presets/mainnet.yaml
@@ -76,7 +76,7 @@ MIN_EPOCHS_TO_INACTIVITY_PENALTY: 4
 # 2**16 (= 65,536) epochs ~0.8 years
 EPOCHS_PER_HISTORICAL_VECTOR: 65536
 # 2**13 (= 8,192) epochs ~36 days
-EPOCHS_PER_SLASHED_BALANCES_VECTOR: 8192
+EPOCHS_PER_SLASHINGS_VECTOR: 8192
 # 2**24 (= 16,777,216) historical roots, ~26,131 years
 HISTORICAL_ROOTS_LIMIT: 16777216
 # 2**40 (= 1,099,511,627,776) validator spots
@@ -88,7 +88,7 @@ VALIDATOR_REGISTRY_LIMIT: 1099511627776
 # 2**5 (= 32)
 BASE_REWARD_FACTOR: 32
 # 2**9 (= 512)
-WHISTLEBLOWING_REWARD_QUOTIENT: 512
+WHISTLEBLOWER_REWARD_QUOTIENT: 512
 # 2**3 (= 8)
 PROPOSER_REWARD_QUOTIENT: 8
 # 2**25 (= 33,554,432)
diff --git a/configs/constant_presets/minimal.yaml b/configs/constant_presets/minimal.yaml
index 417f11c94..27ed9d15e 100644
--- a/configs/constant_presets/minimal.yaml
+++ b/configs/constant_presets/minimal.yaml
@@ -77,7 +77,7 @@ EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS: 4096
 # [customized] smaller state
 EPOCHS_PER_HISTORICAL_VECTOR: 64
 # [customized] smaller state
-EPOCHS_PER_SLASHED_BALANCES_VECTOR: 64
+EPOCHS_PER_SLASHINGS_VECTOR: 64
 # 2**24 (= 16,777,216) historical roots
 HISTORICAL_ROOTS_LIMIT: 16777216
 # 2**40 (= 1,099,511,627,776) validator spots
@@ -89,7 +89,7 @@ VALIDATOR_REGISTRY_LIMIT: 1099511627776
 # 2**5 (= 32)
 BASE_REWARD_FACTOR: 32
 # 2**9 (= 512)
-WHISTLEBLOWING_REWARD_QUOTIENT: 512
+WHISTLEBLOWER_REWARD_QUOTIENT: 512
 # 2**3 (= 8)
 PROPOSER_REWARD_QUOTIENT: 8
 # 2**25 (= 33,554,432)
diff --git a/specs/bls_signature.md b/specs/bls_signature.md
index 3fe1bcc0e..b901b9345 100644
--- a/specs/bls_signature.md
+++ b/specs/bls_signature.md
@@ -71,7 +71,7 @@ We require:
 G2_cofactor = 305502333931268344200999753193121504214466019254188142667664032982267604182971884026507427359259977847832272839041616661285803823378372096355777062779109
 q = 4002409555221667393417789825735904156556882819939007885332058136124031650490837864442687629129015664037894272559787
 
-def hash_to_G2(message_hash: Bytes32, domain: uint64) -> [uint384]:
+def hash_to_G2(message_hash: Bytes32, domain: uint64) -> Tuple[uint384, uint384]:
     # Initial candidate x coordinate
     x_re = int.from_bytes(hash(message_hash + bytes8(domain) + b'\x01'), 'big')
     x_im = int.from_bytes(hash(message_hash + bytes8(domain) + b'\x02'), 'big')
diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 490ac0c96..70a59c41d 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -24,6 +24,7 @@
     - [Containers](#containers)
         - [Misc dependencies](#misc-dependencies)
             - [`Fork`](#fork)
+            - [`Checkpoint`](#checkpoint)
             - [`Validator`](#validator)
             - [`Crosslink`](#crosslink)
             - [`AttestationData`](#attestationdata)
@@ -234,7 +235,7 @@ The following values are (non-configurable) constants used throughout the specif
 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
 | `EPOCHS_PER_HISTORICAL_VECTOR` | `2**16` (= 65,536) | epochs | ~0.8 years |
-| `EPOCHS_PER_SLASHED_BALANCES_VECTOR` | `2**13` (= 8,192) | epochs | ~36 days |
+| `EPOCHS_PER_SLASHINGS_VECTOR` | `2**13` (= 8,192) | epochs | ~36 days |
 | `HISTORICAL_ROOTS_LIMIT` | `2**24` (= 16,777,216) | historical roots | ~26,131 years |
 | `VALIDATOR_REGISTRY_LIMIT` | `2**40` (= 1,099,511,627,776) | validator spots | |
 
@@ -243,7 +244,7 @@ The following values are (non-configurable) constants used throughout the specif
 | Name | Value |
 | - | - |
 | `BASE_REWARD_FACTOR` | `2**6` (= 64) |
-| `WHISTLEBLOWING_REWARD_QUOTIENT` | `2**9` (= 512) |
+| `WHISTLEBLOWER_REWARD_QUOTIENT` | `2**9` (= 512) |
 | `PROPOSER_REWARD_QUOTIENT` | `2**3` (= 8) |
 | `INACTIVITY_PENALTY_QUOTIENT` | `2**25` (= 33,554,432) |
 | `MIN_SLASHING_PENALTY_QUOTIENT` | `2**5` (= 32) |
@@ -291,6 +292,14 @@ class Fork(Container):
     epoch: Epoch  # Epoch of latest fork
 ```
 
+#### `Checkpoint`
+
+```python
+class Checkpoint(Container):
+    epoch: Epoch
+    root: Hash
+```
+
 #### `Validator`
 
 ```python
@@ -325,10 +334,8 @@ class AttestationData(Container):
     # LMD GHOST vote
     beacon_block_root: Hash
     # FFG vote
-    source_epoch: Epoch
-    source_root: Hash
-    target_epoch: Epoch
-    target_root: Hash
+    source: Checkpoint
+    target: Checkpoint
     # Crosslink vote
     crosslink: Crosslink
 ```
@@ -522,22 +529,18 @@ class BeaconState(Container):
     randao_mixes: Vector[Hash, EPOCHS_PER_HISTORICAL_VECTOR]
     compact_committees_roots: Vector[Hash, EPOCHS_PER_HISTORICAL_VECTOR]  # Committee digests for light clients
     # Slashings
-    slashed_balances: Vector[Gwei, EPOCHS_PER_SLASHED_BALANCES_VECTOR]  # Sums of slashed effective balances
+    slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR]  # Per-epoch sums of slashed effective balances
     # Attestations
     previous_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
     current_epoch_attestations: List[PendingAttestation, MAX_ATTESTATIONS * SLOTS_PER_EPOCH]
     # Crosslinks
     previous_crosslinks: Vector[Crosslink, SHARD_COUNT]  # Previous epoch snapshot
     current_crosslinks: Vector[Crosslink, SHARD_COUNT]
-    # Justification
-    previous_justified_epoch: Epoch  # Previous epoch snapshot
-    previous_justified_root: Hash  # Previous epoch snapshot
-    current_justified_epoch: Epoch
-    current_justified_root: Hash
-    justification_bitfield: uint64  # Bit set for every recent justified epoch
     # Finality
-    finalized_epoch: Epoch
-    finalized_root: Hash
+    justification_bitfield: uint64  # Bit set for every recent justified epoch
+    previous_justified_checkpoint: Checkpoint  # Previous epoch snapshot
+    current_justified_checkpoint: Checkpoint
+    finalized_checkpoint: Checkpoint
 ```
 
 ## Helper functions
@@ -714,9 +717,9 @@ 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.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target_epoch)) % SHARD_COUNT
-    return Slot(get_epoch_start_slot(data.target_epoch) + offset // (committee_count // SLOTS_PER_EPOCH))
+    committee_count = get_epoch_committee_count(state, data.target.epoch)
+    offset = (data.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target.epoch)) % SHARD_COUNT
+    return Slot(get_epoch_start_slot(data.target.epoch) + offset // (committee_count // SLOTS_PER_EPOCH))
 ```
 
 ### `get_block_root_at_slot`
@@ -883,15 +886,13 @@ def get_crosslink_committee(state: BeaconState, epoch: Epoch, shard: Shard) -> S
 ### `get_attesting_indices`
 
 ```python
-def get_attesting_indices(state: BeaconState,
-                          attestation_data: AttestationData,
-                          bitfield: bytes) -> Sequence[ValidatorIndex]:
+def get_attesting_indices(state: BeaconState, data: AttestationData, bitfield: bytes) -> Set[ValidatorIndex]:
     """
-    Return the sorted attesting indices corresponding to ``attestation_data`` and ``bitfield``.
+    Return the set of attesting indices corresponding to ``data`` and ``bitfield``.
     """
-    committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.crosslink.shard)
+    committee = get_crosslink_committee(state, data.target.epoch, 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])
+    return set(index for i, index in enumerate(committee) if get_bitfield_bit(bitfield, i) == 0b1)
 ```
 
 ### `int_to_bytes`
@@ -969,12 +970,12 @@ def convert_to_indexed(state: BeaconState, attestation: Attestation) -> IndexedA
     """
     attesting_indices = get_attesting_indices(state, attestation.data, attestation.aggregation_bitfield)
     custody_bit_1_indices = get_attesting_indices(state, attestation.data, attestation.custody_bitfield)
-    assert set(custody_bit_1_indices).issubset(attesting_indices)
-    custody_bit_0_indices = [index for index in attesting_indices if index not in custody_bit_1_indices]
+    assert custody_bit_1_indices.issubset(attesting_indices)
+    custody_bit_0_indices = attesting_indices.difference(custody_bit_1_indices)
 
     return IndexedAttestation(
-        custody_bit_0_indices=custody_bit_0_indices,
-        custody_bit_1_indices=custody_bit_1_indices,
+        custody_bit_0_indices=sorted(custody_bit_0_indices),
+        custody_bit_1_indices=sorted(custody_bit_1_indices),
         data=attestation.data,
         signature=attestation.signature,
     )
@@ -1009,7 +1010,7 @@ def validate_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
             hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b1)),
         ],
         signature=indexed_attestation.signature,
-        domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.target_epoch),
+        domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.target.epoch),
     )
 ```
 
@@ -1022,9 +1023,9 @@ def is_slashable_attestation_data(data_1: AttestationData, data_2: AttestationDa
     """
     return (
         # Double vote
-        (data_1 != data_2 and data_1.target_epoch == data_2.target_epoch) or
+        (data_1 != data_2 and data_1.target.epoch == data_2.target.epoch) or
         # Surround vote
-        (data_1.source_epoch < data_2.source_epoch and data_2.target_epoch < data_1.target_epoch)
+        (data_1.source.epoch < data_2.source.epoch and data_2.target.epoch < data_1.target.epoch)
     )
 ```
 
@@ -1116,21 +1117,22 @@ def slash_validator(state: BeaconState,
     """
     Slash the validator with index ``slashed_index``.
     """
-    current_epoch = get_current_epoch(state)
+    epoch = get_current_epoch(state)
     initiate_validator_exit(state, slashed_index)
-    state.validators[slashed_index].slashed = True
-    state.validators[slashed_index].withdrawable_epoch = Epoch(current_epoch + EPOCHS_PER_SLASHED_BALANCES_VECTOR)
-    slashed_balance = state.validators[slashed_index].effective_balance
-    state.slashed_balances[current_epoch % EPOCHS_PER_SLASHED_BALANCES_VECTOR] += slashed_balance
+    validator = state.validators[slashed_index]
+    validator.slashed = True
+    validator.withdrawable_epoch = max(validator.withdrawable_epoch, Epoch(epoch + EPOCHS_PER_SLASHINGS_VECTOR))
+    state.slashings[epoch % EPOCHS_PER_SLASHINGS_VECTOR] += validator.effective_balance
+    decrease_balance(state, slashed_index, validator.effective_balance // MIN_SLASHING_PENALTY_QUOTIENT)
 
+    # Apply proposer and whistleblower rewards
     proposer_index = get_beacon_proposer_index(state)
     if whistleblower_index is None:
         whistleblower_index = proposer_index
-    whistleblowing_reward = Gwei(slashed_balance // WHISTLEBLOWING_REWARD_QUOTIENT)
-    proposer_reward = Gwei(whistleblowing_reward // PROPOSER_REWARD_QUOTIENT)
+    whistleblower_reward = Gwei(validator.effective_balance // WHISTLEBLOWER_REWARD_QUOTIENT)
+    proposer_reward = Gwei(whistleblower_reward // PROPOSER_REWARD_QUOTIENT)
     increase_balance(state, proposer_index, proposer_reward)
-    increase_balance(state, whistleblower_index, whistleblowing_reward - proposer_reward)
-    decrease_balance(state, slashed_index, whistleblowing_reward)
+    increase_balance(state, whistleblower_index, whistleblower_reward - proposer_reward)
 ```
 
 ## Genesis
@@ -1193,10 +1195,10 @@ def get_genesis_beacon_state(deposits: Sequence[Deposit], genesis_time: int, eth
             validator.activation_eligibility_epoch = GENESIS_EPOCH
             validator.activation_epoch = GENESIS_EPOCH
 
-    # Populate compact_committees_roots
+    # Populate active_index_roots
+    genesis_committee_root = get_compact_committees_root(state, GENESIS_EPOCH)
     for index in range(EPOCHS_PER_HISTORICAL_VECTOR):
-        state.compact_committees_roots[index] = get_compact_committees_root(state, GENESIS_EPOCH)
-
+        state.compact_committees_roots[index] = genesis_committee_root
     return state
 ```
 
@@ -1273,7 +1275,7 @@ def get_total_active_balance(state: BeaconState) -> Gwei:
 
 ```python
 def get_matching_source_attestations(state: BeaconState, epoch: Epoch) -> Sequence[PendingAttestation]:
-    assert epoch in (get_current_epoch(state), get_previous_epoch(state))
+    assert epoch in (get_previous_epoch(state), get_current_epoch(state))
     return state.current_epoch_attestations if epoch == get_current_epoch(state) else state.previous_epoch_attestations
 ```
 
@@ -1281,7 +1283,7 @@ def get_matching_source_attestations(state: BeaconState, epoch: Epoch) -> Sequen
 def get_matching_target_attestations(state: BeaconState, epoch: Epoch) -> Sequence[PendingAttestation]:
     return [
         a for a in get_matching_source_attestations(state, epoch)
-        if a.data.target_root == get_block_root(state, epoch)
+        if a.data.target.root == get_block_root(state, epoch)
     ]
 ```
 
@@ -1333,46 +1335,40 @@ def process_justification_and_finalization(state: BeaconState) -> None:
 
     previous_epoch = get_previous_epoch(state)
     current_epoch = get_current_epoch(state)
-    old_previous_justified_epoch = state.previous_justified_epoch
-    old_current_justified_epoch = state.current_justified_epoch
+    old_previous_justified_checkpoint = state.previous_justified_checkpoint
+    old_current_justified_checkpoint = state.current_justified_checkpoint
 
     # Process justifications
-    state.previous_justified_epoch = state.current_justified_epoch
-    state.previous_justified_root = state.current_justified_root
+    state.previous_justified_checkpoint = state.current_justified_checkpoint
     state.justification_bitfield = (state.justification_bitfield << 1) % 2**64
     previous_epoch_matching_target_balance = get_attesting_balance(
         state, get_matching_target_attestations(state, previous_epoch)
     )
     if previous_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_epoch = previous_epoch
-        state.current_justified_root = get_block_root(state, state.current_justified_epoch)
+        state.current_justified_checkpoint = Checkpoint(epoch=previous_epoch,
+                                                        root=get_block_root(state, previous_epoch))
         state.justification_bitfield |= (1 << 1)
     current_epoch_matching_target_balance = get_attesting_balance(
         state, get_matching_target_attestations(state, current_epoch)
     )
     if current_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_epoch = current_epoch
-        state.current_justified_root = get_block_root(state, state.current_justified_epoch)
+        state.current_justified_checkpoint = Checkpoint(epoch=current_epoch, root=get_block_root(state, current_epoch))
         state.justification_bitfield |= (1 << 0)
 
     # Process finalizations
     bitfield = state.justification_bitfield
     # The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th as source
-    if (bitfield >> 1) % 8 == 0b111 and old_previous_justified_epoch + 3 == current_epoch:
-        state.finalized_epoch = old_previous_justified_epoch
-        state.finalized_root = get_block_root(state, state.finalized_epoch)
+    if (bitfield >> 1) % 8 == 0b111 and old_previous_justified_checkpoint.epoch + 3 == current_epoch:
+        state.finalized_checkpoint = old_previous_justified_checkpoint
     # The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as source
-    if (bitfield >> 1) % 4 == 0b11 and old_previous_justified_epoch + 2 == current_epoch:
-        state.finalized_epoch = old_previous_justified_epoch
-        state.finalized_root = get_block_root(state, state.finalized_epoch)
+    if (bitfield >> 1) % 4 == 0b11 and old_previous_justified_checkpoint.epoch + 2 == current_epoch:
+        state.finalized_checkpoint = old_previous_justified_checkpoint
     # The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as source
-    if (bitfield >> 0) % 8 == 0b111 and old_current_justified_epoch + 2 == current_epoch:
-        state.finalized_epoch = old_current_justified_epoch
-        state.finalized_root = get_block_root(state, state.finalized_epoch)
+    if (bitfield >> 0) % 8 == 0b111 and old_current_justified_checkpoint.epoch + 2 == current_epoch:
+        state.finalized_checkpoint = old_current_justified_checkpoint
     # The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source
-    if (bitfield >> 0) % 4 == 0b11 and old_current_justified_epoch + 1 == current_epoch:
-        state.finalized_epoch = old_current_justified_epoch
-        state.finalized_root = get_block_root(state, state.finalized_epoch)
+    if (bitfield >> 0) % 4 == 0b11 and old_current_justified_checkpoint.epoch + 1 == current_epoch:
+        state.finalized_checkpoint = old_current_justified_checkpoint
 ```
 
 #### Crosslinks
@@ -1435,7 +1431,7 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence
         rewards[index] += Gwei(max_attester_reward * MIN_ATTESTATION_INCLUSION_DELAY // attestation.inclusion_delay)
 
     # Inactivity penalty
-    finality_delay = previous_epoch - state.finalized_epoch
+    finality_delay = previous_epoch - state.finalized_checkpoint.epoch
     if finality_delay > MIN_EPOCHS_TO_INACTIVITY_PENALTY:
         matching_target_attesting_indices = get_unslashed_attesting_indices(state, matching_target_attestations)
         for index in eligible_validator_indices:
@@ -1500,7 +1496,7 @@ def process_registry_updates(state: BeaconState) -> None:
     activation_queue = sorted([
         index for index, validator in enumerate(state.validators) if
         validator.activation_eligibility_epoch != FAR_FUTURE_EPOCH and
-        validator.activation_epoch >= get_delayed_activation_exit_epoch(state.finalized_epoch)
+        validator.activation_epoch >= get_delayed_activation_exit_epoch(state.finalized_checkpoint.epoch)
     ], key=lambda index: state.validators[index].activation_eligibility_epoch)
     # Dequeued validators for activation up to churn limit (without resetting activation epoch)
     for index in activation_queue[:get_churn_limit(state)]:
@@ -1515,18 +1511,9 @@ def process_registry_updates(state: BeaconState) -> None:
 def process_slashings(state: BeaconState) -> None:
     epoch = get_current_epoch(state)
     total_balance = get_total_active_balance(state)
-
-    # Compute slashed balances in the current epoch
-    total_at_start = state.slashed_balances[(epoch + 1) % EPOCHS_PER_SLASHED_BALANCES_VECTOR]
-    total_at_end = state.slashed_balances[epoch % EPOCHS_PER_SLASHED_BALANCES_VECTOR]
-    total_penalties = total_at_end - total_at_start
-
     for index, validator in enumerate(state.validators):
-        if validator.slashed and epoch + EPOCHS_PER_SLASHED_BALANCES_VECTOR // 2 == validator.withdrawable_epoch:
-            penalty = max(
-                validator.effective_balance * min(total_penalties * 3, total_balance) // total_balance,
-                validator.effective_balance // MIN_SLASHING_PENALTY_QUOTIENT
-            )
+        if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch:
+            penalty = validator.effective_balance * min(sum(state.slashings) * 3, total_balance) // total_balance
             decrease_balance(state, ValidatorIndex(index), penalty)
 ```
 
@@ -1548,12 +1535,10 @@ def process_final_updates(state: BeaconState) -> None:
     # Update start shard
     state.start_shard = Shard((state.start_shard + get_shard_delta(state, current_epoch)) % SHARD_COUNT)
     # Set active index root
-    index_root_position = (next_epoch + ACTIVATION_EXIT_DELAY) % EPOCHS_PER_HISTORICAL_VECTOR
-    state.compact_committees_roots[index_root_position] = get_compact_committees_root(state, next_epoch)
-    # Set total slashed balances
-    state.slashed_balances[next_epoch % EPOCHS_PER_SLASHED_BALANCES_VECTOR] = (
-        state.slashed_balances[current_epoch % EPOCHS_PER_SLASHED_BALANCES_VECTOR]
-    )
+    committee_root_position = (next_epoch + ACTIVATION_EXIT_DELAY) % EPOCHS_PER_HISTORICAL_VECTOR
+    state.compact_committees_roots[committee_root_position] = get_compact_committees_root(state, next_epoch)
+    # Reset slashings
+    state.slashings[next_epoch % EPOCHS_PER_SLASHINGS_VECTOR] = Gwei(0)
     # Set randao mix
     state.randao_mixes[next_epoch % EPOCHS_PER_HISTORICAL_VECTOR] = get_randao_mix(state, current_epoch)
     # Set historical root accumulator
@@ -1697,9 +1682,8 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     Process ``Attestation`` operation.
     """
     data = attestation.data
-
     assert data.crosslink.shard < SHARD_COUNT
-    assert data.target_epoch in (get_previous_epoch(state), get_current_epoch(state))
+    assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
 
     attestation_slot = get_attestation_data_slot(state, data)
     assert attestation_slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= attestation_slot + SLOTS_PER_EPOCH
@@ -1711,21 +1695,22 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
         proposer_index=get_beacon_proposer_index(state),
     )
 
-    if data.target_epoch == get_current_epoch(state):
-        ffg_data = (state.current_justified_epoch, state.current_justified_root, get_current_epoch(state))
+    if data.target.epoch == get_current_epoch(state):
+        assert data.source == state.current_justified_checkpoint
         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))
+        assert data.source == state.previous_justified_checkpoint
         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.start_epoch == parent_crosslink.end_epoch
-    assert data.crosslink.end_epoch == min(data.target_epoch, parent_crosslink.end_epoch + MAX_EPOCHS_PER_CROSSLINK)
+    # Check crosslink against expected parent crosslink
     assert data.crosslink.parent_root == hash_tree_root(parent_crosslink)
+    assert data.crosslink.start_epoch == parent_crosslink.end_epoch
+    assert data.crosslink.end_epoch == min(data.target.epoch, parent_crosslink.end_epoch + MAX_EPOCHS_PER_CROSSLINK)
     assert data.crosslink.data_root == ZERO_HASH  # [to be removed in phase 1]
+    
+    # Check signature
     validate_indexed_attestation(state, convert_to_indexed(state, attestation))
 ```
 
@@ -1808,8 +1793,8 @@ def process_transfer(state: BeaconState, transfer: Transfer) -> None:
     """
     Process ``Transfer`` operation.
     """
-    # Verify the amount and fee are not individually too big (for anti-overflow purposes)
-    assert state.balances[transfer.sender] >= max(transfer.amount, transfer.fee)
+    # Verify the balance the covers amount and fee (with overflow protection)
+    assert state.balances[transfer.sender] >= max(transfer.amount + transfer.fee, transfer.amount, transfer.fee)
     # A transfer is valid in only one slot
     assert state.slot == transfer.slot
     # Sender must satisfy at least one of the following conditions in the parenthesis:
diff --git a/specs/core/0_fork-choice.md b/specs/core/0_fork-choice.md
index f896caa3b..c54824f3b 100644
--- a/specs/core/0_fork-choice.md
+++ b/specs/core/0_fork-choice.md
@@ -12,7 +12,7 @@
         - [Time parameters](#time-parameters)
     - [Fork choice](#fork-choice)
         - [Helpers](#helpers)
-            - [`Target`](#target)
+            - [`Checkpoint`](#checkpoint)
             - [`Store`](#store)
             - [`get_genesis_store`](#get_genesis_store)
             - [`get_ancestor`](#get_ancestor)
@@ -55,11 +55,11 @@ The head block root associated with a `store` is defined as `get_head(store)`. A
 
 ### Helpers
 
-#### `Target`
+#### `LatestMessage`
 
 ```python
-@dataclass
-class Target(object):
+@dataclass(eq=True, frozen=True)
+class LatestMessage(object):
     epoch: Epoch
     root: Hash
 ```
@@ -69,12 +69,13 @@ class Target(object):
 ```python
 @dataclass
 class Store(object):
+    time: int
+    justified_checkpoint: Checkpoint
+    finalized_checkpoint: Checkpoint
     blocks: Dict[Hash, BeaconBlock] = field(default_factory=dict)
-    states: Dict[Hash, BeaconState] = field(default_factory=dict)
-    time: int = 0
-    latest_targets: Dict[ValidatorIndex, Target] = field(default_factory=dict)
-    justified_root: Hash = ZERO_HASH
-    finalized_root: Hash = ZERO_HASH
+    block_states: Dict[Hash, BeaconState] = field(default_factory=dict)
+    checkpoint_states: Dict[Checkpoint, BeaconState] = field(default_factory=dict)
+    latest_messages: Dict[ValidatorIndex, LatestMessage] = field(default_factory=dict)
 ```
 
 #### `get_genesis_store`
@@ -83,12 +84,15 @@ class Store(object):
 def get_genesis_store(genesis_state: BeaconState) -> Store:
     genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state))
     root = signing_root(genesis_block)
+    justified_checkpoint = Checkpoint(epoch=GENESIS_EPOCH, root=root)
+    finalized_checkpoint = Checkpoint(epoch=GENESIS_EPOCH, root=root)
     return Store(
-        blocks={root: genesis_block},
-        states={root: genesis_state},
         time=genesis_state.genesis_time,
-        justified_root=root,
-        finalized_root=root,
+        justified_checkpoint=justified_checkpoint,
+        finalized_checkpoint=finalized_checkpoint,
+        blocks={root: genesis_block},
+        block_states={root: genesis_state.copy()},
+        checkpoint_states={justified_checkpoint: genesis_state.copy()},
     )
 ```
 
@@ -105,11 +109,12 @@ def get_ancestor(store: Store, root: Hash, slot: Slot) -> Hash:
 
 ```python
 def get_latest_attesting_balance(store: Store, root: Hash) -> Gwei:
-    state = store.states[store.justified_root]
-    active_indices = get_active_validator_indices(state.validator_registry, get_current_epoch(state))
+    state = store.checkpoint_states[store.justified_checkpoint]
+    active_indices = get_active_validator_indices(state, get_current_epoch(state))
     return Gwei(sum(
-        state.validator_registry[i].effective_balance for i in active_indices
-        if get_ancestor(store, store.latest_targets[i].root, store.blocks[root].slot) == root
+        state.validators[i].effective_balance for i in active_indices
+        if (i in store.latest_messages and
+            get_ancestor(store, store.latest_messages[i].root, store.blocks[root].slot) == root)
     ))
 ```
 
@@ -118,9 +123,13 @@ def get_latest_attesting_balance(store: Store, root: Hash) -> Gwei:
 ```python
 def get_head(store: Store) -> Hash:
     # Execute the LMD-GHOST fork choice
-    head = store.justified_root
+    head = store.justified_checkpoint.root
+    justified_slot = get_epoch_start_slot(store.justified_checkpoint.epoch)
     while True:
-        children = [root for root in store.blocks.keys() if store.blocks[root].parent_root == head]
+        children = [
+            root for root in store.blocks.keys()
+            if store.blocks[root].parent_root == head and store.blocks[root].slot > justified_slot
+        ]
         if len(children) == 0:
             return head
         # Sort by latest attesting balance with ties broken lexicographically
@@ -141,35 +150,65 @@ def on_tick(store: Store, time: int) -> None:
 ```python
 def on_block(store: Store, block: BeaconBlock) -> None:
     # Make a copy of the state to avoid mutability issues
-    pre_state = store.states[block.parent_root].copy()
+    assert block.parent_root in store.block_states
+    pre_state = store.block_states[block.parent_root].copy()
     # Blocks cannot be in the future. If they are, their consideration must be delayed until the are in the past.
     assert store.time >= pre_state.genesis_time + block.slot * SECONDS_PER_SLOT
     # Add new block to the store
     store.blocks[signing_root(block)] = block
     # Check block is a descendant of the finalized block
-    assert get_ancestor(store, signing_root(block), store.blocks[store.finalized_root].slot) == store.finalized_root
+    assert (
+        get_ancestor(store, signing_root(block), store.blocks[store.finalized_checkpoint.root].slot) ==
+        store.finalized_checkpoint.root
+    )
+    # Check that block is later than the finalized epoch slot
+    assert block.slot > get_epoch_start_slot(store.finalized_checkpoint.epoch)
     # Check the block is valid and compute the post-state
     state = state_transition(pre_state, block)
-    # Add new state to the store
-    store.states[signing_root(block)] = state
-    # Update justified block root
-    if state.current_justified_epoch > slot_to_epoch(store.blocks[store.justified_root].slot):
-        store.justified_root = state.current_justified_root
-    elif state.previous_justified_epoch > slot_to_epoch(store.blocks[store.justified_root].slot):
-        store.justified_root = state.previous_justified_root
-    # Update finalized block root
-    if state.finalized_epoch > slot_to_epoch(store.blocks[store.finalized_root].slot):
-        store.finalized_root = state.finalized_root
+    # Add new state for this block to the store
+    store.block_states[signing_root(block)] = state
+
+    # Update justified checkpoint
+    if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
+        store.justified_checkpoint = state.current_justified_checkpoint
+    elif state.previous_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
+        store.justified_checkpoint = state.previous_justified_checkpoint
+
+    # Update finalized checkpoint
+    if state.finalized_checkpoint.epoch > store.finalized_checkpoint.epoch:
+        store.finalized_checkpoint = state.finalized_checkpoint
 ```
 
 #### `on_attestation`
 
 ```python
 def on_attestation(store: Store, attestation: Attestation) -> None:
-    state = store.states[get_head(store)]
-    indexed_attestation = convert_to_indexed(state, attestation)
-    validate_indexed_attestation(state, indexed_attestation)
+    target = attestation.data.target
+
+    # Cannot calculate the current shuffling if have not seen the target
+    assert target.root in store.blocks
+
+    # Attestations cannot be from future epochs. If they are, delay consideration until the epoch arrivesr
+    base_state = store.block_states[target.root].copy()
+    assert store.time >= base_state.genesis_time + get_epoch_start_slot(target.epoch) * SECONDS_PER_SLOT
+
+    # Store target checkpoint state if not yet seen
+    if target not in store.checkpoint_states:
+        process_slots(base_state, get_epoch_start_slot(target.epoch))
+        store.checkpoint_states[target] = base_state
+    target_state = store.checkpoint_states[target]
+
+    # Attestations can only affect the fork choice of subsequent slots.
+    # Delay consideration in the fork choice until their slot is in the past.
+    attestation_slot = get_attestation_data_slot(target_state, attestation.data)
+    assert store.time >= (attestation_slot + 1) * SECONDS_PER_SLOT
+
+    # Get state at the `target` to validate attestation and calculate the committees
+    indexed_attestation = convert_to_indexed(target_state, attestation)
+    validate_indexed_attestation(target_state, indexed_attestation)
+
+    # Update latest messages
     for i in indexed_attestation.custody_bit_0_indices + indexed_attestation.custody_bit_1_indices:
-        if i not in store.latest_targets or attestation.data.target_epoch > store.latest_targets[i].epoch:
-            store.latest_targets[i] = Target(attestation.data.target_epoch, attestation.data.target_root)
+        if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch:
+            store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=attestation.data.beacon_block_root)
 ```
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index 07f6ec698..9b17b39ed 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -36,7 +36,7 @@
         - [`get_custody_chunk_bit`](#get_custody_chunk_bit)
         - [`get_chunk_bits_root`](#get_chunk_bits_root)
         - [`get_randao_epoch_for_custody_period`](#get_randao_epoch_for_custody_period)
-        - [`get_validators_custody_reveal_period`](#get_validators_custody_reveal_period)
+        - [`get_reveal_period`](#get_reveal_period)
         - [`replace_empty_or_append`](#replace_empty_or_append)
     - [Per-block processing](#per-block-processing)
         - [Operations](#operations)
@@ -211,7 +211,7 @@ class EarlyDerivedSecretReveal(Container):
     # Index of the validator who revealed (whistleblower)
     masker_index: ValidatorIndex
     # Mask used to hide the actual reveal signature (prevent reveal from being stolen)
-    mask: Bytes32
+    mask: Hash
 ```
 
 ### Phase 0 container updates
@@ -224,7 +224,7 @@ Add the following fields to the end of the specified container objects. Fields w
 class Validator(Container):
     # next_custody_reveal_period is initialised to the custody period
     # (of the particular validator) in which the validator is activated
-    # = get_validators_custody_reveal_period(...)
+    # = get_reveal_period(...)
     next_custody_reveal_period: uint64
     max_reveal_lateness: uint64
 ```
@@ -299,17 +299,12 @@ def get_randao_epoch_for_custody_period(period: int, validator_index: ValidatorI
     return Epoch(next_period_start + CUSTODY_PERIOD_TO_RANDAO_PADDING)
 ```
 
-### `get_validators_custody_reveal_period`
+### `get_reveal_period`
 
 ```python
-def get_validators_custody_reveal_period(state: BeaconState,
-                                         validator_index: ValidatorIndex,
-                                         epoch: Epoch=None) -> int:
+def get_reveal_period(state: BeaconState, validator_index: ValidatorIndex, epoch: Epoch=None) -> int:
     '''
-    This function returns the reveal period for a given validator.
-    If no epoch is supplied, the current epoch is assumed.
-    Note: This function implicitly requires that validators are not removed from the
-    validator set in fewer than EPOCHS_PER_CUSTODY_PERIOD epochs
+    Return the reveal period for a given validator.
     '''
     epoch = get_current_epoch(state) if epoch is None else epoch
     return (epoch + validator_index % EPOCHS_PER_CUSTODY_PERIOD) // EPOCHS_PER_CUSTODY_PERIOD
@@ -340,17 +335,15 @@ Verify that `len(block.body.custody_key_reveals) <= MAX_CUSTODY_KEY_REVEALS`.
 For each `reveal` in `block.body.custody_key_reveals`, run the following function:
 
 ```python
-def process_custody_key_reveal(state: BeaconState,
-                               reveal: CustodyKeyReveal) -> None:
+def process_custody_key_reveal(state: BeaconState, reveal: CustodyKeyReveal) -> None:
     """
     Process ``CustodyKeyReveal`` operation.
     Note that this function mutates ``state``.
     """
-
     revealer = state.validators[reveal.revealer_index]
     epoch_to_sign = get_randao_epoch_for_custody_period(revealer.next_custody_reveal_period, reveal.revealed_index)
 
-    assert revealer.next_custody_reveal_period < get_validators_custody_reveal_period(state, reveal.revealed_index)
+    assert revealer.next_custody_reveal_period < get_reveal_period(state, reveal.revealed_index)
 
     # Revealed validator is active or exited, but not withdrawn
     assert is_slashable_validator(revealer, get_current_epoch(state))
@@ -368,11 +361,11 @@ def process_custody_key_reveal(state: BeaconState,
     )
 
     # Decrement max reveal lateness if response is timely
-    if revealer.next_custody_reveal_period == get_validators_custody_reveal_period(state, reveal.revealer_index) - 2:
+    if revealer.next_custody_reveal_period == get_reveal_period(state, reveal.revealer_index) - 2:
         revealer.max_reveal_lateness -= MAX_REVEAL_LATENESS_DECREMENT
     revealer.max_reveal_lateness = max(
         revealer.max_reveal_lateness,
-        get_validators_custody_reveal_period(state, reveal.revealed_index) - revealer.next_custody_reveal_period
+        get_reveal_period(state, reveal.revealed_index) - revealer.next_custody_reveal_period
     )
 
     # Process reveal
@@ -394,13 +387,11 @@ Verify that `len(block.body.early_derived_secret_reveals) <= MAX_EARLY_DERIVED_S
 For each `reveal` in `block.body.early_derived_secret_reveals`, run the following function:
 
 ```python
-def process_early_derived_secret_reveal(state: BeaconState,
-                                        reveal: EarlyDerivedSecretReveal) -> None:
+def process_early_derived_secret_reveal(state: BeaconState, reveal: EarlyDerivedSecretReveal) -> None:
     """
     Process ``EarlyDerivedSecretReveal`` operation.
     Note that this function mutates ``state``.
     """
-
     revealed_validator = state.validators[reveal.revealed_index]
     derived_secret_location = reveal.epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS
 
@@ -453,7 +444,7 @@ def process_early_derived_secret_reveal(state: BeaconState,
         # Apply penalty
         proposer_index = get_beacon_proposer_index(state)
         whistleblower_index = reveal.masker_index
-        whistleblowing_reward = Gwei(penalty // WHISTLEBLOWING_REWARD_QUOTIENT)
+        whistleblowing_reward = Gwei(penalty // WHISTLEBLOWER_REWARD_QUOTIENT)
         proposer_reward = Gwei(whistleblowing_reward // PROPOSER_REWARD_QUOTIENT)
         increase_balance(state, proposer_index, proposer_reward)
         increase_balance(state, whistleblower_index, whistleblowing_reward - proposer_reward)
@@ -470,8 +461,7 @@ Verify that `len(block.body.custody_chunk_challenges) <= MAX_CUSTODY_CHUNK_CHALL
 For each `challenge` in `block.body.custody_chunk_challenges`, run the following function:
 
 ```python
-def process_chunk_challenge(state: BeaconState,
-                            challenge: CustodyChunkChallenge) -> None:
+def process_chunk_challenge(state: BeaconState, challenge: CustodyChunkChallenge) -> None:
     # Verify the attestation
     validate_indexed_attestation(state, convert_to_indexed(state, challenge.attestation))
     # Verify it is not too late to challenge
@@ -514,59 +504,41 @@ Verify that `len(block.body.custody_bit_challenges) <= MAX_CUSTODY_BIT_CHALLENGE
 For each `challenge` in `block.body.custody_bit_challenges`, run the following function:
 
 ```python
-def process_bit_challenge(state: BeaconState,
-                          challenge: CustodyBitChallenge) -> None:
+def process_bit_challenge(state: BeaconState, challenge: CustodyBitChallenge) -> None:
+    attestation = challenge.attestation
+    epoch = slot_to_epoch(attestation.data.slot)
+    shard = attestation.data.crosslink.shard
 
     # Verify challenge signature
     challenger = state.validators[challenge.challenger_index]
-    assert bls_verify(
-        pubkey=challenger.pubkey,
-        message_hash=signing_root(challenge),
-        signature=challenge.signature,
-        domain=get_domain(state, DOMAIN_CUSTODY_BIT_CHALLENGE, get_current_epoch(state)),
-    )
+    domain = get_domain(state, DOMAIN_CUSTODY_BIT_CHALLENGE, get_current_epoch(state))
+    assert bls_verify(challenger.pubkey, signing_root(challenge), challenge.signature, domain)
+    # Verify challenger is slashable
     assert is_slashable_validator(challenger, get_current_epoch(state))
-
-    # Verify the attestation
-    attestation = challenge.attestation
+    # Verify attestation
     validate_indexed_attestation(state, convert_to_indexed(state, attestation))
-    # Verify the attestation is eligible for challenging
+    # Verify attestation is eligible for challenging
     responder = state.validators[challenge.responder_index]
-    assert (slot_to_epoch(attestation.data.slot) + responder.max_reveal_lateness <=
-            get_validators_custody_reveal_period(state, challenge.responder_index))
-
-    # Verify the responder participated in the attestation
+    assert epoch + responder.max_reveal_lateness <= get_reveal_period(state, challenge.responder_index)
+    # Verify responder participated in the attestation
     attesters = get_attesting_indices(state, attestation.data, attestation.aggregation_bitfield)
     assert challenge.responder_index in attesters
-
-    # A validator can be the challenger for at most one challenge at a time
+    # Verifier challenger is not already challenging
     for record in state.custody_bit_challenge_records:
         assert record.challenger_index != challenge.challenger_index
-
-    # Verify the responder is a valid custody key
+    # Verify the responder custody key
     epoch_to_sign = get_randao_epoch_for_custody_period(
-        get_validators_custody_reveal_period(
-            state,
-            challenge.responder_index,
-            epoch=slot_to_epoch(attestation.data.slot)),
-        challenge.responder_index
+        get_reveal_period(state, challenge.responder_index, epoch),
+        challenge.responder_index,
     )
-    assert bls_verify(
-        pubkey=responder.pubkey,
-        message_hash=hash_tree_root(epoch_to_sign),
-        signature=challenge.responder_key,
-        domain=get_domain(
-            state=state,
-            domain_type=DOMAIN_RANDAO,
-            message_epoch=epoch_to_sign,
-        ),
-    )
-
+    domain = get_domain(state, DOMAIN_RANDAO, epoch_to_sign)
+    assert bls_verify(responder.pubkey, hash_tree_root(epoch_to_sign), challenge.responder_key, domain)
     # Verify the chunk count
     chunk_count = get_custody_chunk_count(attestation.data.crosslink)
     assert verify_bitfield(challenge.chunk_bits, chunk_count)
     # Verify the first bit of the hash of the chunk bits does not equal the custody bit
-    custody_bit = get_bitfield_bit(attestation.custody_bitfield, attesters.index(challenge.responder_index))
+    committee = get_crosslink_committee(state, epoch, shard)
+    custody_bit = get_bitfield_bit(attestation.custody_bitfield, committee.index(challenge.responder_index))
     assert custody_bit != get_bitfield_bit(get_chunk_bits_root(challenge.chunk_bits), 0)
     # Add new bit challenge record
     new_record = CustodyBitChallengeRecord(
@@ -581,7 +553,6 @@ def process_bit_challenge(state: BeaconState,
     )
     replace_empty_or_append(state.custody_bit_challenge_records, new_record)
     state.custody_challenge_index += 1
-
     # Postpone responder withdrawability
     responder.withdrawable_epoch = FAR_FUTURE_EPOCH
 ```
@@ -593,8 +564,7 @@ Verify that `len(block.body.custody_responses) <= MAX_CUSTODY_RESPONSES`.
 For each `response` in `block.body.custody_responses`, run the following function:
 
 ```python
-def process_custody_response(state: BeaconState,
-                             response: CustodyResponse) -> None:
+def process_custody_response(state: BeaconState, response: CustodyResponse) -> None:
     chunk_challenge = next((record for record in state.custody_chunk_challenge_records
                             if record.challenge_index == response.challenge_index), None)
     if chunk_challenge is not None:
@@ -682,7 +652,7 @@ Run `process_reveal_deadlines(state)` immediately after `process_registry_update
 def process_reveal_deadlines(state: BeaconState) -> None:
     for index, validator in enumerate(state.validators):
         deadline = validator.next_custody_reveal_period + (CUSTODY_RESPONSE_DEADLINE // EPOCHS_PER_CUSTODY_PERIOD)
-        if get_validators_custody_reveal_period(state, ValidatorIndex(index)) > deadline:
+        if get_reveal_period(state, ValidatorIndex(index)) > deadline:
             slash_validator(state, ValidatorIndex(index))
 ```
 
diff --git a/specs/validator/0_beacon-chain-validator.md b/specs/validator/0_beacon-chain-validator.md
index aa8350b66..44b5e2a3c 100644
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@@ -221,19 +221,26 @@ epoch_signature = bls_sign(
 
 ##### Eth1 Data
 
-`block.eth1_data` is a mechanism used by block proposers vote on a recent Ethereum 1.0 block hash and an associated deposit root found in the Ethereum 1.0 deposit contract. When consensus is formed, `state.eth1_data` is updated, and validator deposits up to this root can be processed. The deposit root can be calculated by calling the `get_deposit_root()` function of the deposit contract using the post-state of the block hash.
+The `block.eth1_data` field is for block proposers to vote on recent Eth 1.0 data. This recent data contains an Eth 1.0 block hash as well as the associated deposit root (as calculated by the `get_deposit_root()` method of the deposit contract) and deposit count after execution of the corresponding Eth 1.0 block. If over half of the block proposers in the current Eth 1.0 voting period vote for the same `eth1_data` then `state.eth1_data` updates at the end of the voting period. Each deposit in `block.body.deposits` must verify against `state.eth1_data.eth1_deposit_root`.
 
-* Let `D` be the list of `Eth1DataVote` objects `vote` in `state.eth1_data_votes` where:
-    * `vote.eth1_data.block_hash` is the hash of an Eth 1.0 block that is (i) part of the canonical chain, (ii) >= `ETH1_FOLLOW_DISTANCE` blocks behind the head, and (iii) newer than `state.eth1_data.block_hash`.
-    * `vote.eth1_data.deposit_count` is the deposit count of the Eth 1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
-    * `vote.eth1_data.deposit_root` is the deposit root of the Eth 1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
-* If `D` is empty:
-    * Let `block_hash` be the block hash of the `ETH1_FOLLOW_DISTANCE`'th ancestor of the head of the canonical Eth 1.0 chain.
-    * Let `deposit_root` and `deposit_count` be the deposit root and deposit count of the Eth 1.0 deposit contract in the post-state of the block referenced by `block_hash`
-    * Let `best_vote_data = Eth1Data(block_hash=block_hash, deposit_root=deposit_root, deposit_count=deposit_count)`.
-* If `D` is nonempty:
-    * Let `best_vote_data` be the `eth1_data` member of `D` that has the highest vote count (`D.count(eth1_data)`), breaking ties by favoring block hashes with higher associated block height.
-* Set `block.eth1_data = best_vote_data`.
+Let `get_eth1_data(distance: int) -> Eth1Data` be the (subjective) function that returns the Eth 1.0 data at distance `distance` relative to the Eth 1.0 head at the start of the current Eth 1.0 voting period. Let `previous_eth1_distance` be the distance relative to the Eth 1.0 block corresponding to `state.eth1_data.block_hash` at the start of the current Eth 1.0 voting period. An honest block proposer sets `block.eth1_data = get_eth1_vote(state, previous_eth1_distance)` where:
+
+```python
+def get_eth1_vote(state: BeaconState, previous_eth1_distance: uint64) -> Eth1Data:
+    new_eth1_data = [get_eth1_data(distance) for distance in range(ETH1_FOLLOW_DISTANCE, 2 * ETH1_FOLLOW_DISTANCE)]
+    all_eth1_data = [get_eth1_data(distance) for distance in range(ETH1_FOLLOW_DISTANCE, previous_eth1_distance)]
+
+    valid_votes = []
+    for slot, vote in enumerate(state.eth1_data_votes):
+        period_tail = slot % SLOTS_PER_ETH1_VOTING_PERIOD >= integer_square_root(SLOTS_PER_ETH1_VOTING_PERIOD)
+        if vote in new_eth1_data or (period_tail and vote in all_eth1_data):
+            valid_votes.append(vote)
+
+    return max(valid_votes,
+        key=lambda v: (valid_votes.count(v), -all_eth1_data.index(v)),  # Tiebreak by smallest distance
+        default=get_eth1_data(ETH1_FOLLOW_DISTANCE),
+    )
+```
 
 ##### Signature
 
diff --git a/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py b/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py
new file mode 100644
index 000000000..6ac46ba6c
--- /dev/null
+++ b/test_libs/pyspec/eth2spec/test/fork_choice/test_get_head.py
@@ -0,0 +1,118 @@
+from eth2spec.test.context import with_all_phases, with_state, bls_switch
+from eth2spec.test.helpers.attestations import get_valid_attestation
+from eth2spec.test.helpers.block import build_empty_block_for_next_slot
+from eth2spec.test.helpers.state import state_transition_and_sign_block
+
+
+def add_block_to_store(spec, store, block):
+    pre_state = store.block_states[block.parent_root]
+    block_time = pre_state.genesis_time + block.slot * spec.SECONDS_PER_SLOT
+
+    if store.time < block_time:
+        spec.on_tick(store, block_time)
+
+    spec.on_block(store, block)
+
+
+def add_attestation_to_store(spec, store, attestation):
+    parent_block = store.blocks[attestation.data.beacon_block_root]
+    pre_state = store.block_states[spec.signing_root(parent_block)]
+    block_time = pre_state.genesis_time + parent_block.slot * spec.SECONDS_PER_SLOT
+    next_epoch_time = block_time + spec.SLOTS_PER_EPOCH * spec.SECONDS_PER_SLOT
+
+    if store.time < next_epoch_time:
+        spec.on_tick(store, next_epoch_time)
+
+    spec.on_attestation(store, attestation)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_genesis(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    genesis_block = spec.BeaconBlock(state_root=state.hash_tree_root())
+    assert spec.get_head(store) == spec.signing_root(genesis_block)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_chain_no_attestations(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    genesis_block = spec.BeaconBlock(state_root=state.hash_tree_root())
+    assert spec.get_head(store) == spec.signing_root(genesis_block)
+
+    # On receiving a block of `GENESIS_SLOT + 1` slot
+    block_1 = build_empty_block_for_next_slot(spec, state)
+    state_transition_and_sign_block(spec, state, block_1)
+    add_block_to_store(spec, store, block_1)
+
+    # On receiving a block of next epoch
+    block_2 = build_empty_block_for_next_slot(spec, state)
+    state_transition_and_sign_block(spec, state, block_2)
+    add_block_to_store(spec, store, block_2)
+
+    assert spec.get_head(store) == spec.signing_root(block_2)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_split_tie_breaker_no_attestations(spec, state):
+    genesis_state = state.copy()
+
+    # Initialization
+    store = spec.get_genesis_store(state)
+    genesis_block = spec.BeaconBlock(state_root=state.hash_tree_root())
+    assert spec.get_head(store) == spec.signing_root(genesis_block)
+
+    # block at slot 1
+    block_1_state = genesis_state.copy()
+    block_1 = build_empty_block_for_next_slot(spec, block_1_state)
+    state_transition_and_sign_block(spec, block_1_state, block_1)
+    add_block_to_store(spec, store, block_1)
+
+    # additional block at slot 1
+    block_2_state = genesis_state.copy()
+    block_2 = build_empty_block_for_next_slot(spec, block_2_state)
+    block_2.body.graffiti = b'\x42' * 32
+    state_transition_and_sign_block(spec, block_2_state, block_2)
+    add_block_to_store(spec, store, block_2)
+
+    highest_root = max(spec.signing_root(block_1), spec.signing_root(block_2))
+
+    assert spec.get_head(store) == highest_root
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_shorter_chain_but_heavier_weight(spec, state):
+    genesis_state = state.copy()
+
+    # Initialization
+    store = spec.get_genesis_store(state)
+    genesis_block = spec.BeaconBlock(state_root=state.hash_tree_root())
+    assert spec.get_head(store) == spec.signing_root(genesis_block)
+
+    # build longer tree
+    long_state = genesis_state.copy()
+    for i in range(3):
+        long_block = build_empty_block_for_next_slot(spec, long_state)
+        state_transition_and_sign_block(spec, long_state, long_block)
+        add_block_to_store(spec, store, long_block)
+
+    # build short tree
+    short_state = genesis_state.copy()
+    short_block = build_empty_block_for_next_slot(spec, short_state)
+    short_block.body.graffiti = b'\x42' * 32
+    state_transition_and_sign_block(spec, short_state, short_block)
+    add_block_to_store(spec, store, short_block)
+
+    short_attestation = get_valid_attestation(spec, short_state, short_block.slot, signed=True)
+    add_attestation_to_store(spec, store, short_attestation)
+
+    assert spec.get_head(store) == spec.signing_root(short_block)
diff --git a/test_libs/pyspec/eth2spec/test/fork_choice/test_on_attestation.py b/test_libs/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
new file mode 100644
index 000000000..eb1e9a9ed
--- /dev/null
+++ b/test_libs/pyspec/eth2spec/test/fork_choice/test_on_attestation.py
@@ -0,0 +1,122 @@
+from eth2spec.test.context import with_all_phases, with_state, bls_switch
+
+from eth2spec.test.helpers.block import build_empty_block_for_next_slot
+from eth2spec.test.helpers.attestations import get_valid_attestation
+from eth2spec.test.helpers.state import next_slot
+
+
+def run_on_attestation(spec, state, store, attestation, valid=True):
+    if not valid:
+        try:
+            spec.on_attestation(store, attestation)
+        except AssertionError:
+            return
+        else:
+            assert False
+
+    indexed_attestation = spec.convert_to_indexed(state, attestation)
+    spec.on_attestation(store, attestation)
+    assert (
+        store.latest_messages[indexed_attestation.custody_bit_0_indices[0]] ==
+        spec.LatestMessage(
+            epoch=attestation.data.target.epoch,
+            root=attestation.data.beacon_block_root,
+        )
+    )
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_attestation(spec, state):
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    block = build_empty_block_for_next_slot(spec, state, signed=True)
+
+    # store block in store
+    spec.on_block(store, block)
+
+    next_slot(spec, state)
+
+    attestation = get_valid_attestation(spec, state, slot=block.slot)
+    run_on_attestation(spec, state, store, attestation)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_attestation_target_not_in_store(spec, state):
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    # move to next epoch to make block new target
+    state.slot += spec.SLOTS_PER_EPOCH
+
+    block = build_empty_block_for_next_slot(spec, state, signed=True)
+
+    # do not add block to store
+
+    next_slot(spec, state)
+    attestation = get_valid_attestation(spec, state, slot=block.slot)
+    run_on_attestation(spec, state, store, attestation, False)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_attestation_future_epoch(spec, state):
+    store = spec.get_genesis_store(state)
+    time = 3 * spec.SECONDS_PER_SLOT
+    spec.on_tick(store, time)
+
+    block = build_empty_block_for_next_slot(spec, state, signed=True)
+
+    # store block in store
+    spec.on_block(store, block)
+    next_slot(spec, state)
+
+    # move state forward but not store
+    attestation_slot = block.slot + spec.SLOTS_PER_EPOCH
+    state.slot = attestation_slot
+
+    attestation = get_valid_attestation(spec, state, slot=state.slot)
+    run_on_attestation(spec, state, store, attestation, False)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_attestation_same_slot(spec, state):
+    store = spec.get_genesis_store(state)
+    time = 1 * spec.SECONDS_PER_SLOT
+    spec.on_tick(store, time)
+
+    block = build_empty_block_for_next_slot(spec, state, signed=True)
+
+    spec.on_block(store, block)
+    next_slot(spec, state)
+
+    attestation = get_valid_attestation(spec, state, slot=block.slot)
+    run_on_attestation(spec, state, store, attestation, False)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_attestation_invalid_attestation(spec, state):
+    store = spec.get_genesis_store(state)
+    time = 3 * spec.SECONDS_PER_SLOT
+    spec.on_tick(store, time)
+
+    block = build_empty_block_for_next_slot(spec, state, signed=True)
+
+    spec.on_block(store, block)
+    next_slot(spec, state)
+
+    attestation = get_valid_attestation(spec, state, slot=block.slot)
+    # make attestation invalid
+    attestation.custody_bitfield = b'\xf0' + attestation.custody_bitfield[1:]
+    run_on_attestation(spec, state, store, attestation, False)
diff --git a/test_libs/pyspec/eth2spec/test/fork_choice/test_on_block.py b/test_libs/pyspec/eth2spec/test/fork_choice/test_on_block.py
new file mode 100644
index 000000000..158ee1a58
--- /dev/null
+++ b/test_libs/pyspec/eth2spec/test/fork_choice/test_on_block.py
@@ -0,0 +1,89 @@
+from eth2spec.utils.ssz.ssz_impl import signing_root
+
+from eth2spec.test.context import with_all_phases, with_state, bls_switch
+from eth2spec.test.helpers.block import build_empty_block_for_next_slot
+
+
+def run_on_block(spec, state, store, block, valid=True):
+    if not valid:
+        try:
+            spec.on_block(store, block)
+        except AssertionError:
+            return
+        else:
+            assert False
+
+    spec.on_block(store, block)
+    assert store.blocks[signing_root(block)] == block
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_basic(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+    assert store.time == time
+
+    # On receiving a block of `GENESIS_SLOT + 1` slot
+    block = build_empty_block_for_next_slot(spec, state)
+    run_on_block(spec, state, store, block)
+
+    # On receiving a block of next epoch
+    store.time = time + spec.SECONDS_PER_SLOT * spec.SLOTS_PER_EPOCH
+    block = build_empty_block_for_next_slot(spec, state)
+    block.slot += spec.SLOTS_PER_EPOCH
+
+    run_on_block(spec, state, store, block)
+
+    # TODO: add tests for justified_root and finalized_root
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_block_future_block(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+
+    # do not tick time
+
+    # Fail receiving block of `GENESIS_SLOT + 1` slot
+    block = build_empty_block_for_next_slot(spec, state)
+    run_on_block(spec, state, store, block, False)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_block_bad_parent_root(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    # Fail receiving block of `GENESIS_SLOT + 1` slot
+    block = build_empty_block_for_next_slot(spec, state)
+    block.parent_root = b'\x45' * 32
+    run_on_block(spec, state, store, block, False)
+
+
+@with_all_phases
+@with_state
+@bls_switch
+def test_on_block_before_finalized(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    store.finalized_checkpoint = spec.Checkpoint(
+        epoch=store.finalized_checkpoint.epoch + 2,
+        root=store.finalized_checkpoint.root
+    )
+
+    # Fail receiving block of `GENESIS_SLOT + 1` slot
+    block = build_empty_block_for_next_slot(spec, state)
+    run_on_block(spec, state, store, block, False)
diff --git a/test_libs/pyspec/eth2spec/test/helpers/attestations.py b/test_libs/pyspec/eth2spec/test/helpers/attestations.py
index 4c8b5c7eb..d717bdc0d 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/attestations.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/attestations.py
@@ -24,11 +24,11 @@ def build_attestation_data(spec, state, slot, shard):
         epoch_boundary_root = spec.get_block_root(state, spec.get_current_epoch(state))
 
     if slot < current_epoch_start_slot:
-        justified_epoch = state.previous_justified_epoch
-        justified_block_root = state.previous_justified_root
+        source_epoch = state.previous_justified_checkpoint.epoch
+        source_root = state.previous_justified_checkpoint.root
     else:
-        justified_epoch = state.current_justified_epoch
-        justified_block_root = state.current_justified_root
+        source_epoch = state.current_justified_checkpoint.epoch
+        source_root = state.current_justified_checkpoint.root
 
     if spec.slot_to_epoch(slot) == spec.get_current_epoch(state):
         parent_crosslink = state.current_crosslinks[shard]
@@ -37,10 +37,8 @@ def build_attestation_data(spec, state, slot, shard):
 
     return spec.AttestationData(
         beacon_block_root=block_root,
-        source_epoch=justified_epoch,
-        source_root=justified_block_root,
-        target_epoch=spec.slot_to_epoch(slot),
-        target_root=epoch_boundary_root,
+        source=spec.Checkpoint(epoch=source_epoch, root=source_root),
+        target=spec.Checkpoint(epoch=spec.slot_to_epoch(slot), root=epoch_boundary_root),
         crosslink=spec.Crosslink(
             shard=shard,
             start_epoch=parent_crosslink.end_epoch,
@@ -64,8 +62,8 @@ def get_valid_attestation(spec, state, slot=None, signed=False):
 
     crosslink_committee = spec.get_crosslink_committee(
         state,
-        attestation_data.target_epoch,
-        attestation_data.crosslink.shard
+        attestation_data.target.epoch,
+        attestation_data.crosslink.shard,
     )
 
     committee_size = len(crosslink_committee)
@@ -126,7 +124,7 @@ def get_attestation_signature(spec, state, attestation_data, privkey, custody_bi
         domain=spec.get_domain(
             state=state,
             domain_type=spec.DOMAIN_ATTESTATION,
-            message_epoch=attestation_data.target_epoch,
+            message_epoch=attestation_data.target.epoch,
         )
     )
 
@@ -134,7 +132,7 @@ def get_attestation_signature(spec, state, attestation_data, privkey, custody_bi
 def fill_aggregate_attestation(spec, state, attestation):
     crosslink_committee = spec.get_crosslink_committee(
         state,
-        attestation.data.target_epoch,
+        attestation.data.target.epoch,
         attestation.data.crosslink.shard,
     )
     for i in range(len(crosslink_committee)):
diff --git a/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py b/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
index 9fd34520c..9c68b7bbe 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
@@ -7,7 +7,7 @@ def get_valid_attester_slashing(spec, state, signed_1=False, signed_2=False):
     attestation_1 = get_valid_attestation(spec, state, signed=signed_1)
 
     attestation_2 = deepcopy(attestation_1)
-    attestation_2.data.target_root = b'\x01' * 32
+    attestation_2.data.target.root = b'\x01' * 32
 
     if signed_2:
         sign_attestation(spec, state, attestation_2)
diff --git a/test_libs/pyspec/eth2spec/test/helpers/custody.py b/test_libs/pyspec/eth2spec/test/helpers/custody.py
index cd34ee4c8..36f23ad1c 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/custody.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/custody.py
@@ -1,5 +1,6 @@
 from eth2spec.test.helpers.keys import privkeys
-from eth2spec.utils.bls import bls_sign
+from eth2spec.utils.bls import bls_sign, bls_aggregate_signatures
+from eth2spec.utils.hash_function import hash
 
 
 def get_valid_early_derived_secret_reveal(spec, state, epoch=None):
@@ -10,6 +11,7 @@ def get_valid_early_derived_secret_reveal(spec, state, epoch=None):
     if epoch is None:
         epoch = current_epoch + spec.CUSTODY_PERIOD_TO_RANDAO_PADDING
 
+    # Generate the secret that is being revealed
     reveal = bls_sign(
         message_hash=spec.hash_tree_root(spec.Epoch(epoch)),
         privkey=privkeys[revealed_index],
@@ -19,20 +21,24 @@ def get_valid_early_derived_secret_reveal(spec, state, epoch=None):
             message_epoch=epoch,
         ),
     )
-    mask = bls_sign(
-        message_hash=spec.hash_tree_root(spec.Epoch(epoch)),
+    # Generate the mask (any random 32 bytes that don't reveal the masker's secret will do)
+    mask = hash(reveal)
+    # Generate masker's signature on the mask
+    masker_signature = bls_sign(
+        message_hash=mask,
         privkey=privkeys[masker_index],
         domain=spec.get_domain(
             state=state,
             domain_type=spec.DOMAIN_RANDAO,
             message_epoch=epoch,
         ),
-    )[:32]  # TODO(Carl): mask is 32 bytes, and signature is 96? Correct to slice the first 32 out?
+    )
+    masked_reveal = bls_aggregate_signatures([reveal, masker_signature])
 
     return spec.EarlyDerivedSecretReveal(
         revealed_index=revealed_index,
         epoch=epoch,
-        reveal=reveal,
+        reveal=masked_reveal,
         masker_index=masker_index,
         mask=mask,
     )
diff --git a/test_libs/pyspec/eth2spec/test/helpers/genesis.py b/test_libs/pyspec/eth2spec/test/helpers/genesis.py
index c793254c8..7ffacd7d0 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/genesis.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/genesis.py
@@ -28,7 +28,9 @@ def create_genesis_state(spec, num_validators):
             deposit_root=deposit_root,
             deposit_count=num_validators,
             block_hash=spec.ZERO_HASH,
-        ))
+        ),
+        latest_block_header=spec.BeaconBlockHeader(body_root=spec.hash_tree_root(spec.BeaconBlockBody())),
+    )
 
     # We "hack" in the initial validators,
     #  as it is much faster than creating and processing genesis deposits for every single test case.
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
index 2b34ab405..d4e22decf 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
@@ -38,7 +38,7 @@ def run_attestation_processing(spec, state, attestation, valid=True):
     spec.process_attestation(state, attestation)
 
     # Make sure the attestation has been processed
-    if attestation.data.target_epoch == spec.get_current_epoch(state):
+    if attestation.data.target.epoch == spec.get_current_epoch(state):
         assert len(state.current_epoch_attestations) == current_epoch_count + 1
     else:
         assert len(state.previous_epoch_attestations) == previous_epoch_count + 1
@@ -119,16 +119,16 @@ def test_after_epoch_slots(spec, state):
 @spec_state_test
 def test_old_source_epoch(spec, state):
     state.slot = spec.SLOTS_PER_EPOCH * 5
-    state.finalized_epoch = 2
-    state.previous_justified_epoch = 3
-    state.current_justified_epoch = 4
+    state.finalized_checkpoint.epoch = 2
+    state.previous_justified_checkpoint.epoch = 3
+    state.current_justified_checkpoint.epoch = 4
     attestation = get_valid_attestation(spec, state, slot=(spec.SLOTS_PER_EPOCH * 3) + 1)
 
     # test logic sanity check: make sure the attestation is pointing to oldest known source epoch
-    assert attestation.data.source_epoch == state.previous_justified_epoch
+    assert attestation.data.source.epoch == state.previous_justified_checkpoint.epoch
 
     # Now go beyond that, it will be invalid
-    attestation.data.source_epoch -= 1
+    attestation.data.source.epoch -= 1
 
     sign_attestation(spec, state, attestation)
 
@@ -154,7 +154,7 @@ def test_new_source_epoch(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_epoch += 1
+    attestation.data.source.epoch += 1
 
     sign_attestation(spec, state, attestation)
 
@@ -167,7 +167,7 @@ def test_source_root_is_target_root(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_root = attestation.data.target_root
+    attestation.data.source.root = attestation.data.target.root
 
     sign_attestation(spec, state, attestation)
 
@@ -178,23 +178,20 @@ def test_source_root_is_target_root(spec, state):
 @spec_state_test
 def test_invalid_current_source_root(spec, state):
     state.slot = spec.SLOTS_PER_EPOCH * 5
-    state.finalized_epoch = 2
+    state.finalized_checkpoint.epoch = 2
 
-    state.previous_justified_epoch = 3
-    state.previous_justified_root = b'\x01' * 32
-
-    state.current_justified_epoch = 4
-    state.current_justified_root = b'\xff' * 32
+    state.previous_justified_checkpoint = spec.Checkpoint(epoch=3, root=b'\x01' * 32)
+    state.current_justified_checkpoint = spec.Checkpoint(epoch=4, root=b'\x32' * 32)
 
     attestation = get_valid_attestation(spec, state, slot=(spec.SLOTS_PER_EPOCH * 3) + 1)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
     # Test logic sanity checks:
-    assert state.current_justified_root != state.previous_justified_root
-    assert attestation.data.source_root == state.previous_justified_root
+    assert state.current_justified_checkpoint.root != state.previous_justified_checkpoint.root
+    assert attestation.data.source.root == state.previous_justified_checkpoint.root
 
     # Make attestation source root invalid: should be previous justified, not current one
-    attestation.data.source_root = state.current_justified_root
+    attestation.data.source.root = state.current_justified_checkpoint.root
 
     sign_attestation(spec, state, attestation)
 
@@ -207,7 +204,7 @@ def test_bad_source_root(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_root = b'\x42' * 32
+    attestation.data.source.root = b'\x42' * 32
 
     sign_attestation(spec, state, attestation)
 
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
index c51f5a8a9..e78e1a866 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
@@ -25,31 +25,56 @@ def run_attester_slashing_processing(spec, state, attester_slashing, valid=True)
         yield 'post', None
         return
 
-    slashed_index = attester_slashing.attestation_1.custody_bit_0_indices[0]
-    pre_slashed_balance = get_balance(state, slashed_index)
+    slashed_indices = (
+        attester_slashing.attestation_1.custody_bit_0_indices
+        + attester_slashing.attestation_1.custody_bit_1_indices
+    )
 
     proposer_index = spec.get_beacon_proposer_index(state)
     pre_proposer_balance = get_balance(state, proposer_index)
+    pre_slashings = {slashed_index: get_balance(state, slashed_index) for slashed_index in slashed_indices}
+    pre_withdrawalable_epochs = {
+        slashed_index: state.validators[slashed_index].withdrawable_epoch
+        for slashed_index in slashed_indices
+    }
+
+    total_proposer_rewards = sum(
+        balance // spec.WHISTLEBLOWER_REWARD_QUOTIENT
+        for balance in pre_slashings.values()
+    )
 
     # Process slashing
     spec.process_attester_slashing(state, attester_slashing)
 
-    slashed_validator = state.validators[slashed_index]
+    for slashed_index in slashed_indices:
+        pre_withdrawalable_epoch = pre_withdrawalable_epochs[slashed_index]
+        slashed_validator = state.validators[slashed_index]
 
-    # Check slashing
-    assert slashed_validator.slashed
-    assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
-    assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
+        # Check slashing
+        assert slashed_validator.slashed
+        assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
+        if pre_withdrawalable_epoch < spec.FAR_FUTURE_EPOCH:
+            expected_withdrawable_epoch = max(
+                pre_withdrawalable_epoch,
+                spec.get_current_epoch(state) + spec.EPOCHS_PER_SLASHINGS_VECTOR
+            )
+            assert slashed_validator.withdrawable_epoch == expected_withdrawable_epoch
+        else:
+            assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
+        assert get_balance(state, slashed_index) < pre_slashings[slashed_index]
 
-    if slashed_index != proposer_index:
-        # lost whistleblower reward
-        assert get_balance(state, slashed_index) < pre_slashed_balance
+    if proposer_index not in slashed_indices:
         # gained whistleblower reward
-        assert get_balance(state, proposer_index) > pre_proposer_balance
+        assert get_balance(state, proposer_index) == pre_proposer_balance + total_proposer_rewards
     else:
         # gained rewards for all slashings, which may include others. And only lost that of themselves.
-        # Netto at least 0, if more people where slashed, a balance increase.
-        assert get_balance(state, slashed_index) >= pre_slashed_balance
+        expected_balance = (
+            pre_proposer_balance
+            + total_proposer_rewards
+            - pre_slashings[proposer_index] // spec.MIN_SLASHING_PENALTY_QUOTIENT
+        )
+
+        assert get_balance(state, proposer_index) == expected_balance
 
     yield 'post', state
 
@@ -68,18 +93,51 @@ def test_success_surround(spec, state):
     next_epoch(spec, state)
     apply_empty_block(spec, state)
 
-    state.current_justified_epoch += 1
+    state.current_justified_checkpoint.epoch += 1
     attester_slashing = get_valid_attester_slashing(spec, state, signed_1=False, signed_2=True)
+    attestation_1 = attester_slashing.attestation_1
+    attestation_2 = attester_slashing.attestation_2
 
     # set attestion1 to surround attestation 2
-    attester_slashing.attestation_1.data.source_epoch = attester_slashing.attestation_2.data.source_epoch - 1
-    attester_slashing.attestation_1.data.target_epoch = attester_slashing.attestation_2.data.target_epoch + 1
+    attestation_1.data.source.epoch = attestation_2.data.source.epoch - 1
+    attestation_1.data.target.epoch = attestation_2.data.target.epoch + 1
 
     sign_indexed_attestation(spec, state, attester_slashing.attestation_1)
 
     yield from run_attester_slashing_processing(spec, state, attester_slashing)
 
 
+@with_all_phases
+@always_bls
+@spec_state_test
+def test_success_already_exited_recent(spec, state):
+    attester_slashing = get_valid_attester_slashing(spec, state, signed_1=True, signed_2=True)
+    slashed_indices = (
+        attester_slashing.attestation_1.custody_bit_0_indices
+        + attester_slashing.attestation_1.custody_bit_1_indices
+    )
+    for index in slashed_indices:
+        spec.initiate_validator_exit(state, index)
+
+    yield from run_attester_slashing_processing(spec, state, attester_slashing)
+
+
+@with_all_phases
+@always_bls
+@spec_state_test
+def test_success_already_exited_long_ago(spec, state):
+    attester_slashing = get_valid_attester_slashing(spec, state, signed_1=True, signed_2=True)
+    slashed_indices = (
+        attester_slashing.attestation_1.custody_bit_0_indices
+        + attester_slashing.attestation_1.custody_bit_1_indices
+    )
+    for index in slashed_indices:
+        spec.initiate_validator_exit(state, index)
+        state.validators[index].withdrawable_epoch = spec.get_current_epoch(state) + 2
+
+    yield from run_attester_slashing_processing(spec, state, attester_slashing)
+
+
 @with_all_phases
 @always_bls
 @spec_state_test
@@ -120,7 +178,7 @@ def test_same_data(spec, state):
 def test_no_double_or_surround(spec, state):
     attester_slashing = get_valid_attester_slashing(spec, state, signed_1=False, signed_2=True)
 
-    attester_slashing.attestation_1.data.target_epoch += 1
+    attester_slashing.attestation_1.data.target.epoch += 1
     sign_indexed_attestation(spec, state, attester_slashing.attestation_1)
 
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_transfer.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_transfer.py
index e9d282b3a..89246cc51 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_transfer.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_transfer.py
@@ -114,7 +114,7 @@ def test_incorrect_slot(spec, state):
 
 @with_all_phases
 @spec_state_test
-def test_insufficient_balance_for_fee(spec, state):
+def test_insufficient_balance_for_fee_result_dust(spec, state):
     sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
     state.balances[sender_index] = spec.MAX_EFFECTIVE_BALANCE
     transfer = get_valid_transfer(spec, state, sender_index=sender_index, amount=0, fee=1, signed=True)
@@ -127,7 +127,20 @@ def test_insufficient_balance_for_fee(spec, state):
 
 @with_all_phases
 @spec_state_test
-def test_insufficient_balance(spec, state):
+def test_insufficient_balance_for_fee_result_full(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=0, fee=state.balances[sender_index] + 1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_amount_result_dust(spec, state):
     sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
     state.balances[sender_index] = spec.MAX_EFFECTIVE_BALANCE
     transfer = get_valid_transfer(spec, state, sender_index=sender_index, amount=1, fee=0, signed=True)
@@ -138,6 +151,127 @@ def test_insufficient_balance(spec, state):
     yield from run_transfer_processing(spec, state, transfer, False)
 
 
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_amount_result_full(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=state.balances[sender_index] + 1, fee=0, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_combined_result_dust(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee without dust, and amount without dust, but not both.
+    state.balances[sender_index] = spec.MIN_DEPOSIT_AMOUNT + 1
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index, amount=1, fee=1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_combined_result_full(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    state.balances[sender_index] = spec.MIN_DEPOSIT_AMOUNT * 2 + 1
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=spec.MIN_DEPOSIT_AMOUNT + 1,
+                                  fee=spec.MIN_DEPOSIT_AMOUNT + 1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_combined_big_amount(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    # Try to create a dust balance (off by 1) with combination of fee and amount.
+    state.balances[sender_index] = spec.MIN_DEPOSIT_AMOUNT * 2 + 1
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=spec.MIN_DEPOSIT_AMOUNT + 1, fee=1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_for_combined_big_fee(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    # Try to create a dust balance (off by 1) with combination of fee and amount.
+    state.balances[sender_index] = spec.MIN_DEPOSIT_AMOUNT * 2 + 1
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=1, fee=spec.MIN_DEPOSIT_AMOUNT + 1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_off_by_1_fee(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    # Try to print money by using the full balance as amount, plus 1 for fee.
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=state.balances[sender_index], fee=1, signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_off_by_1_amount(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    # Try to print money by using the full balance as fee, plus 1 for amount.
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index, amount=1,
+                                  fee=state.balances[sender_index], signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_insufficient_balance_duplicate_as_fee_and_amount(spec, state):
+    sender_index = spec.get_active_validator_indices(state, spec.get_current_epoch(state))[-1]
+    # Enough to pay fee fully without dust left, and amount fully without dust left, but not both.
+    # Try to print money by using the full balance, twice.
+    transfer = get_valid_transfer(spec, state, sender_index=sender_index,
+                                  amount=state.balances[sender_index],
+                                  fee=state.balances[sender_index], signed=True)
+
+    # un-activate so validator can transfer
+    state.validators[transfer.sender].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+
+    yield from run_transfer_processing(spec, state, transfer, False)
+
+
 @with_all_phases
 @spec_state_test
 def test_no_dust_sender(spec, state):
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
index d51191efb..090858a2e 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
@@ -96,7 +96,7 @@ def test_single_crosslink_update_from_previous_epoch(spec, state):
     # ensure rewarded
     for index in spec.get_crosslink_committee(
             state,
-            attestation.data.target_epoch,
+            attestation.data.target.epoch,
             attestation.data.crosslink.shard):
         assert crosslink_deltas[0][index] > 0
         assert crosslink_deltas[1][index] == 0
@@ -148,7 +148,7 @@ def test_double_late_crosslink(spec, state):
     # ensure no reward, only penalties for the failed crosslink
     for index in spec.get_crosslink_committee(
             state,
-            attestation_2.data.target_epoch,
+            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/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py b/test_libs/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
index 87297d443..831ad35a5 100644
--- a/test_libs/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
+++ b/test_libs/pyspec/eth2spec/test/phase_1/block_processing/test_process_early_derived_secret_reveal.py
@@ -1,7 +1,13 @@
 from eth2spec.test.helpers.custody import get_valid_early_derived_secret_reveal
 from eth2spec.test.helpers.block import apply_empty_block
 from eth2spec.test.helpers.state import next_epoch, get_balance
-from eth2spec.test.context import with_all_phases_except, spec_state_test, expect_assertion_error
+from eth2spec.test.context import (
+    with_all_phases_except,
+    spec_state_test,
+    expect_assertion_error,
+    always_bls,
+    never_bls,
+)
 
 
 def run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, valid=True):
@@ -36,6 +42,7 @@ def run_early_derived_secret_reveal_processing(spec, state, randao_key_reveal, v
 
 
 @with_all_phases_except(['phase0'])
+@always_bls
 @spec_state_test
 def test_success(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(spec, state)
@@ -44,6 +51,7 @@ def test_success(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@never_bls
 @spec_state_test
 def test_reveal_from_current_epoch(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(spec, state, spec.get_current_epoch(state))
@@ -52,6 +60,7 @@ def test_reveal_from_current_epoch(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@never_bls
 @spec_state_test
 def test_reveal_from_past_epoch(spec, state):
     next_epoch(spec, state)
@@ -62,6 +71,7 @@ def test_reveal_from_past_epoch(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@always_bls
 @spec_state_test
 def test_reveal_with_custody_padding(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(
@@ -73,6 +83,7 @@ def test_reveal_with_custody_padding(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@always_bls
 @spec_state_test
 def test_reveal_with_custody_padding_minus_one(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(
@@ -84,6 +95,7 @@ def test_reveal_with_custody_padding_minus_one(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@never_bls
 @spec_state_test
 def test_double_reveal(spec, state):
     randao_key_reveal1 = get_valid_early_derived_secret_reveal(
@@ -108,6 +120,7 @@ def test_double_reveal(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@never_bls
 @spec_state_test
 def test_revealer_is_slashed(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(spec, state, spec.get_current_epoch(state))
@@ -117,6 +130,7 @@ def test_revealer_is_slashed(spec, state):
 
 
 @with_all_phases_except(['phase0'])
+@never_bls
 @spec_state_test
 def test_far_future_epoch(spec, state):
     randao_key_reveal = get_valid_early_derived_secret_reveal(
diff --git a/test_libs/pyspec/eth2spec/test/test_finality.py b/test_libs/pyspec/eth2spec/test/test_finality.py
index cf9e94a71..2d86ef523 100644
--- a/test_libs/pyspec/eth2spec/test/test_finality.py
+++ b/test_libs/pyspec/eth2spec/test/test_finality.py
@@ -13,25 +13,22 @@ def check_finality(spec,
                    previous_justified_changed,
                    finalized_changed):
     if current_justified_changed:
-        assert state.current_justified_epoch > prev_state.current_justified_epoch
-        assert state.current_justified_root != prev_state.current_justified_root
+        assert state.current_justified_checkpoint.epoch > prev_state.current_justified_checkpoint.epoch
+        assert state.current_justified_checkpoint.root != prev_state.current_justified_checkpoint.root
     else:
-        assert state.current_justified_epoch == prev_state.current_justified_epoch
-        assert state.current_justified_root == prev_state.current_justified_root
+        assert state.current_justified_checkpoint == prev_state.current_justified_checkpoint
 
     if previous_justified_changed:
-        assert state.previous_justified_epoch > prev_state.previous_justified_epoch
-        assert state.previous_justified_root != prev_state.previous_justified_root
+        assert state.previous_justified_checkpoint.epoch > prev_state.previous_justified_checkpoint.epoch
+        assert state.previous_justified_checkpoint.root != prev_state.previous_justified_checkpoint.root
     else:
-        assert state.previous_justified_epoch == prev_state.previous_justified_epoch
-        assert state.previous_justified_root == prev_state.previous_justified_root
+        assert state.previous_justified_checkpoint == prev_state.previous_justified_checkpoint
 
     if finalized_changed:
-        assert state.finalized_epoch > prev_state.finalized_epoch
-        assert state.finalized_root != prev_state.finalized_root
+        assert state.finalized_checkpoint.epoch > prev_state.finalized_checkpoint.epoch
+        assert state.finalized_checkpoint.root != prev_state.finalized_checkpoint.root
     else:
-        assert state.finalized_epoch == prev_state.finalized_epoch
-        assert state.finalized_root == prev_state.finalized_root
+        assert state.finalized_checkpoint == prev_state.finalized_checkpoint
 
 
 def next_epoch_with_attestations(spec,
@@ -107,8 +104,7 @@ def test_finality_rule_4(spec, state):
         elif epoch == 1:
             # rule 4 of finality
             check_finality(spec, state, prev_state, True, True, True)
-            assert state.finalized_epoch == prev_state.current_justified_epoch
-            assert state.finalized_root == prev_state.current_justified_root
+            assert state.finalized_checkpoint == prev_state.current_justified_checkpoint
 
     yield 'blocks', blocks
     yield 'post', state
@@ -138,8 +134,7 @@ def test_finality_rule_1(spec, state):
         elif epoch == 2:
             # finalized by rule 1
             check_finality(spec, state, prev_state, True, True, True)
-            assert state.finalized_epoch == prev_state.previous_justified_epoch
-            assert state.finalized_root == prev_state.previous_justified_root
+            assert state.finalized_checkpoint == prev_state.previous_justified_checkpoint
 
     yield 'blocks', blocks
     yield 'post', state
@@ -169,8 +164,7 @@ def test_finality_rule_2(spec, state):
             prev_state, new_blocks, state = next_epoch_with_attestations(spec, state, False, True)
             # finalized by rule 2
             check_finality(spec, state, prev_state, True, False, True)
-            assert state.finalized_epoch == prev_state.previous_justified_epoch
-            assert state.finalized_root == prev_state.previous_justified_root
+            assert state.finalized_checkpoint == prev_state.previous_justified_checkpoint
 
         blocks += new_blocks
 
@@ -221,8 +215,7 @@ def test_finality_rule_3(spec, state):
     blocks += new_blocks
     # rule 3
     check_finality(spec, state, prev_state, True, True, True)
-    assert state.finalized_epoch == prev_state.current_justified_epoch
-    assert state.finalized_root == prev_state.current_justified_root
+    assert state.finalized_checkpoint == prev_state.current_justified_checkpoint
 
     yield 'blocks', blocks
     yield 'post', state
diff --git a/test_libs/pyspec/eth2spec/test/test_fork_choice.py b/test_libs/pyspec/eth2spec/test/test_fork_choice.py
deleted file mode 100644
index 4706f0eaf..000000000
--- a/test_libs/pyspec/eth2spec/test/test_fork_choice.py
+++ /dev/null
@@ -1,60 +0,0 @@
-from eth2spec.utils.ssz.ssz_impl import signing_root, hash_tree_root
-
-from eth2spec.test.context import with_all_phases, with_state, bls_switch
-
-from eth2spec.test.helpers.block import build_empty_block_for_next_slot
-from eth2spec.test.helpers.attestations import get_valid_attestation
-from eth2spec.test.helpers.state import next_slot
-
-
-@with_all_phases
-@with_state
-@bls_switch
-def test_basic(spec, state):
-    state.latest_block_header = spec.BeaconBlockHeader(body_root=hash_tree_root(spec.BeaconBlockBody()))
-
-    # Initialization
-    store = spec.get_genesis_store(state)
-    blocks = []
-    time = 100
-    spec.on_tick(store, time)
-    assert store.time == time
-
-    # On receiving a block of `GENESIS_SLOT + 1` slot
-    block = build_empty_block_for_next_slot(spec, state)
-    blocks.append(block)
-    spec.on_block(store, block)
-    assert store.blocks[signing_root(block)] == block
-
-    # On receiving a block of next epoch
-    store.time = time + spec.SECONDS_PER_SLOT * spec.SLOTS_PER_EPOCH
-    block = build_empty_block_for_next_slot(spec, state)
-    block.slot += spec.SLOTS_PER_EPOCH
-    blocks.append(block)
-
-    spec.on_block(store, block)
-    assert store.blocks[signing_root(block)] == block
-
-    # TODO: add tests for justified_root and finalized_root
-
-
-@with_all_phases
-@with_state
-@bls_switch
-def test_on_attestation(spec, state):
-    store = spec.get_genesis_store(state)
-    time = 100
-    spec.on_tick(store, time)
-
-    next_slot(spec, state)
-
-    attestation = get_valid_attestation(spec, state, slot=1)
-    indexed_attestation = spec.convert_to_indexed(state, attestation)
-    spec.on_attestation(store, attestation)
-    assert (
-        store.latest_targets[indexed_attestation.custody_bit_0_indices[0]] ==
-        spec.Target(
-            epoch=attestation.data.target_epoch,
-            root=attestation.data.target_root,
-        )
-    )