From 56309342c05d324e359591b902abc355fba82fb1 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <jacek@status.im>
Date: Thu, 21 May 2020 15:33:47 +0200
Subject: [PATCH 01/31] Use `Bytes32` for `error_message`

`ErrorMessage.error_message` is a leftover from an older version of SSZ
that was able to encode unbounded lists. This is no longer the case -
all collection types now have a fixed upper bound on length.

In general, the `error_message`, just like the `graffitti` field, should
not be interpreted in any particular way except for debugging and vanity
- as such, using the same type, a `Bytes32`, seems reasonable.

An alternative would be `List[byte, 256]` which maybe could be
"reasonably backwards compatible" with whatever clients are are doing
now - depending on how they are dealing with this field type that no
longer exists in the SSZ spec :) It would however be the only place
where `List[uintN, N]` is used in the current spec.

As an exercise, this could be considered a security issue since it's
essentially unbounded and undefined behaviour.
---
 specs/phase0/p2p-interface.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index 118be8839a..84db361c93 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -391,11 +391,11 @@ The `ErrorMessage` schema is:
 
 ```
 (
-  error_message: String
+  error_message: Bytes32
 )
 ```
 
-*Note*: The String type is encoded as UTF-8 bytes without NULL terminator when SSZ-encoded. As the `ErrorMessage` is not an SSZ-container, only the UTF-8 bytes will be sent when SSZ-encoded.
+*Note*: By convention, the `error_message` is a sequence of bytes that can be interpreted as a UTF-8 string up to 32 bytes - a 0 byte shortens the string in this interpretation. Clients MUST treat as valid any bytes.
 
 ### Encoding strategies
 

From 5e8457e62d1272e36de0f55ce3e83543258cddf1 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Sat, 23 May 2020 21:53:55 +0800
Subject: [PATCH 02/31] Fix phase1 on-time sign_indexed_attestation

---
 tests/core/pyspec/eth2spec/test/helpers/attestations.py      | 5 ++++-
 .../block_processing/test_process_attester_slashing.py       | 3 +--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/tests/core/pyspec/eth2spec/test/helpers/attestations.py b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
index 79f752411a..4d246c8c67 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attestations.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
@@ -211,7 +211,10 @@ def sign_indexed_attestation(spec, state, indexed_attestation):
             indexed_attestation.attestation.aggregation_bits,
         )
         data = indexed_attestation.attestation.data
-        indexed_attestation.attestation.signature = sign_aggregate_attestation(spec, state, data, participants)
+        if any(indexed_attestation.attestation.custody_bits_blocks):
+            sign_on_time_attestation(spec, state, indexed_attestation.attestation)
+        else:
+            indexed_attestation.attestation.signature = sign_aggregate_attestation(spec, state, data, participants)
 
 
 def sign_on_time_attestation(spec, state, attestation):
diff --git a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
index 8d7638f518..11ead60337 100644
--- a/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
+++ b/tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
@@ -1,6 +1,6 @@
 from eth2spec.test.context import (
     PHASE0, PHASE1,
-    spec_state_test, expect_assertion_error, always_bls, never_bls, with_all_phases, with_phases
+    spec_state_test, expect_assertion_error, always_bls, with_all_phases, with_phases
 )
 from eth2spec.test.helpers.attestations import sign_indexed_attestation
 from eth2spec.test.helpers.attester_slashings import get_valid_attester_slashing, \
@@ -89,7 +89,6 @@ def test_success_double(spec, state):
 
 @with_all_phases
 @spec_state_test
-@never_bls
 def test_success_surround(spec, state):
     next_epoch_via_block(spec, state)
 

From ce1d22d71c3758b77d3b2e3a0b00efc9d5c5d4cd Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Sat, 23 May 2020 15:22:49 -0700
Subject: [PATCH 03/31] Use helper `compute_previous_slot`

---
 specs/phase1/beacon-chain.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 3bb01e2629..d14e3bce4a 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -801,7 +801,7 @@ def apply_shard_transition(state: BeaconState, shard: Shard, transition: ShardTr
 
     # Save updated state
     state.shard_states[shard] = transition.shard_states[len(transition.shard_states) - 1]
-    state.shard_states[shard].slot = state.slot - 1
+    state.shard_states[shard].slot = compute_previous_slot(state.slot)
 ```
 
 ###### `process_crosslink_for_shard`
@@ -953,7 +953,7 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
 def verify_shard_transition_false_positives(state: BeaconState, block_body: BeaconBlockBody) -> None:
     # Verify that a `shard_transition` in a block is empty if an attestation was not processed for it
     for shard in range(get_active_shard_count(state)):
-        if state.shard_states[shard].slot != state.slot - 1:
+        if state.shard_states[shard].slot != compute_previous_slot(state.slot):
             assert block_body.shard_transitions[shard] == ShardTransition()
 ```
 

From d3c26d6b8b16f130a340568b3caf93a31ae2203e Mon Sep 17 00:00:00 2001
From: ericsson <avv49@mail.ru>
Date: Mon, 25 May 2020 18:45:38 +0300
Subject: [PATCH 04/31] `compute_shard_transition_digest` expects `Root` as a
 fourth parameter

---
 specs/phase1/shard-transition.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 55b867faa9..da3aa648c8 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -81,7 +81,7 @@ def shard_state_transition(beacon_state: BeaconState,
         beacon_state,
         shard_state,
         block.beacon_parent_root,
-        block.body,
+        hash_tree_root(block.body),
     )
     shard_state.gasprice = compute_updated_gasprice(prev_gasprice, len(block.body))
     shard_state.slot = block.slot

From 75787d92a8645751338350ea7d95cf27cb8119fa Mon Sep 17 00:00:00 2001
From: Ali Atiia <42751398+aliatiia@users.noreply.github.com>
Date: Mon, 25 May 2020 16:45:44 -0400
Subject: [PATCH 05/31] broken link

broken link to custory-game.md
---
 specs/phase1/beacon-chain.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 3bb01e2629..321b828cc1 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -997,7 +997,7 @@ def process_epoch(state: BeaconState) -> None:
 
 #### Custody game updates
 
-`process_reveal_deadlines` and `process_custody_final_updates` are defined in [the Custody Game spec](./1_custody-game.md), 
+`process_reveal_deadlines` and `process_custody_final_updates` are defined in [the Custody Game spec](./custody-game.md), 
 
 #### Online-tracking
 

From 75633cfcf1139858d002fe01c68d5f37d22bc28b Mon Sep 17 00:00:00 2001
From: Alex Stokes <r.alex.stokes@gmail.com>
Date: Tue, 26 May 2020 11:00:02 -0700
Subject: [PATCH 06/31] Update link so gossipsub encodings match the correct
 section

---
 specs/phase0/p2p-interface.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index 118be8839a..a994b0c66d 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -203,7 +203,7 @@ Topics are plain UTF-8 strings and are encoded on the wire as determined by prot
     - `current_fork_version` is the fork version of the epoch of the message to be sent on the topic
     - `genesis_validators_root` is the static `Root` found in `state.genesis_validators_root`
 - `Name` - see table below
-- `Encoding` - the encoding strategy describes a specific representation of bytes that will be transmitted over the wire. See the [Encodings](#Encoding-strategies) section for further details.
+- `Encoding` - the encoding strategy describes a specific representation of bytes that will be transmitted over the wire. See the [Encodings](#Encodings) section for further details.
 
 *Note*: `ForkDigestValue` is composed of values that are not known until the genesis block/state are available. Due to this, clients SHOULD NOT subscribe to gossipsub topics until these genesis values are known.
 

From c437578280a3be99c5f2e9c61ad39ff14dbbdaa7 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 28 May 2020 21:32:27 +0800
Subject: [PATCH 07/31] Add `shard` field to `ShardBlock`

---
 specs/phase1/beacon-chain.md                           | 5 ++++-
 specs/phase1/shard-transition.md                       | 1 +
 tests/core/pyspec/eth2spec/test/helpers/shard_block.py | 1 +
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 0ae4bae2b1..39a73c0aa0 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -302,6 +302,7 @@ class ShardBlock(Container):
     shard_parent_root: Root
     beacon_parent_root: Root
     slot: Slot
+    shard: Shard
     proposer_index: ValidatorIndex
     body: ByteList[MAX_SHARD_BLOCK_SIZE]
 ```
@@ -321,6 +322,7 @@ class ShardBlockHeader(Container):
     shard_parent_root: Root
     beacon_parent_root: Root
     slot: Slot
+    shard: Shard
     proposer_index: ValidatorIndex
     body_root: Root
 ```
@@ -781,8 +783,9 @@ def apply_shard_transition(state: BeaconState, shard: Shard, transition: ShardTr
             header = ShardBlockHeader(
                 shard_parent_root=shard_parent_root,
                 beacon_parent_root=get_block_root_at_slot(state, offset_slots[i]),
-                proposer_index=proposal_index,
                 slot=offset_slots[i],
+                shard=shard,
+                proposer_index=proposal_index,
                 body_root=transition.shard_data_roots[i]
             )
             shard_parent_root = hash_tree_root(header)
diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index da3aa648c8..53402bb2a1 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -50,6 +50,7 @@ def verify_shard_block_message(beacon_state: BeaconState,
                                shard: Shard) -> bool:
     assert block.shard_parent_root == shard_state.latest_block_root
     assert block.slot == slot
+    assert block.shard == shard
     assert block.proposer_index == get_shard_proposer_index(beacon_state, slot, shard)
     assert 0 < len(block.body) <= MAX_SHARD_BLOCK_SIZE
     return True
diff --git a/tests/core/pyspec/eth2spec/test/helpers/shard_block.py b/tests/core/pyspec/eth2spec/test/helpers/shard_block.py
index ef65d24279..805b955f79 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/shard_block.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/shard_block.py
@@ -38,6 +38,7 @@ def build_shard_block(spec,
         shard_parent_root=shard_state.latest_block_root,
         beacon_parent_root=beacon_parent_root,
         slot=slot,
+        shard=shard,
         proposer_index=proposer_index,
         body=body,
     )

From ca489630325aebffca2a425fe1a5b69573140e6e Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 28 May 2020 21:38:11 +0800
Subject: [PATCH 08/31] Rename `head_shard_root` to `shard_head_root`

---
 specs/phase1/beacon-chain.md                            | 4 ++--
 tests/core/pyspec/eth2spec/test/helpers/attestations.py | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 0ae4bae2b1..bc5a6385cf 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -130,7 +130,7 @@ class AttestationData(Container):
     source: Checkpoint
     target: Checkpoint
     # Current-slot shard block root
-    head_shard_root: Root
+    shard_head_root: Root
     # Shard transition root
     shard_transition_root: Root
 ```
@@ -823,7 +823,7 @@ def process_crosslink_for_shard(state: BeaconState,
         for attestation in transition_attestations:
             participants = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
             transition_participants = transition_participants.union(participants)
-            assert attestation.data.head_shard_root == shard_transition.shard_data_roots[
+            assert attestation.data.shard_head_root == shard_transition.shard_data_roots[
                 len(shard_transition.shard_data_roots) - 1
             ]
 
diff --git a/tests/core/pyspec/eth2spec/test/helpers/attestations.py b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
index 4d246c8c67..c533182eff 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/attestations.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/attestations.py
@@ -78,7 +78,7 @@ def build_attestation_data(spec, state, slot, index, shard_transition=None, on_t
     if spec.fork == PHASE1:
         if shard_transition is not None:
             lastest_shard_data_root_index = len(shard_transition.shard_data_roots) - 1
-            attestation_data.head_shard_root = shard_transition.shard_data_roots[lastest_shard_data_root_index]
+            attestation_data.shard_head_root = shard_transition.shard_data_roots[lastest_shard_data_root_index]
             attestation_data.shard_transition_root = shard_transition.hash_tree_root()
         else:
             # No shard transition
@@ -88,10 +88,10 @@ def build_attestation_data(spec, state, slot, index, shard_transition=None, on_t
                 next_slot(spec, temp_state)
                 shard_transition = spec.get_shard_transition(temp_state, shard, [])
                 lastest_shard_data_root_index = len(shard_transition.shard_data_roots) - 1
-                attestation_data.head_shard_root = shard_transition.shard_data_roots[lastest_shard_data_root_index]
+                attestation_data.shard_head_root = shard_transition.shard_data_roots[lastest_shard_data_root_index]
                 attestation_data.shard_transition_root = shard_transition.hash_tree_root()
             else:
-                attestation_data.head_shard_root = state.shard_states[shard].transition_digest
+                attestation_data.shard_head_root = state.shard_states[shard].transition_digest
                 attestation_data.shard_transition_root = spec.Root()
     return attestation_data
 

From 8c9bbc48d8720ed621ba54ab7ae12696ca5279e8 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 28 May 2020 21:49:36 +0800
Subject: [PATCH 09/31] Rework `is_shard_attestation`

Change it to `is_on_time_attestation` so that it could be reused in
`validate_attestation`.
---
 specs/phase1/beacon-chain.md | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index bc5a6385cf..4f4713f703 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -53,7 +53,7 @@
     - [`get_offset_slots`](#get_offset_slots)
   - [Predicates](#predicates)
     - [Updated `is_valid_indexed_attestation`](#updated-is_valid_indexed_attestation)
-    - [`is_shard_attestation`](#is_shard_attestation)
+    - [`is_on_time_attestation`](#is_on_time_attestation)
     - [`is_winning_attestation`](#is_winning_attestation)
     - [`optional_aggregate_verify`](#optional_aggregate_verify)
     - [`optional_fast_aggregate_verify`](#optional_fast_aggregate_verify)
@@ -602,20 +602,16 @@ def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
         return bls.AggregateVerify(all_pubkeys, all_signing_roots, signature=attestation.signature)
 ```
 
-#### `is_shard_attestation`
+#### `is_on_time_attestation`
 
 ```python
-def is_shard_attestation(state: BeaconState,
-                         attestation: Attestation,
-                         committee_index: CommitteeIndex) -> bool:
-    if not (
-        attestation.data.index == committee_index
-        and attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY == state.slot  # Must be on-time attestation
-        # TODO: MIN_ATTESTATION_INCLUSION_DELAY should always be 1
-    ):
-        return False
-
-    return True
+def is_on_time_attestation(state: BeaconState,
+                           attestation: Attestation) -> bool:
+    """
+    Check if the given attestation is on-time.
+    """
+    # TODO: MIN_ATTESTATION_INCLUSION_DELAY should always be 1
+    return attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY == state.slot
 ```
 
 #### `is_winning_attestation`
@@ -730,7 +726,7 @@ def validate_attestation(state: BeaconState, attestation: Attestation) -> None:
     # Type 1: on-time attestations, the custody bits should be non-empty.
     if attestation.custody_bits_blocks != []:
         # Ensure on-time attestation
-        assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY == state.slot
+        assert is_on_time_attestation(state, attestation)
         # Correct data root count
         assert len(attestation.custody_bits_blocks) == len(get_offset_slots(state, shard))
         # Correct parent block root
@@ -875,7 +871,7 @@ def process_crosslinks(state: BeaconState,
         shard_transition = shard_transitions[shard]
         shard_attestations = [
             attestation for attestation in attestations
-            if is_shard_attestation(state, attestation, committee_index)
+            if is_on_time_attestation(state, attestation) and attestation.data.index == committee_index
         ]
 
         winning_root = process_crosslink_for_shard(state, committee_index, shard_transition, shard_attestations)

From 19262888e4997659f1a6c015562284213526d0fa Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 28 May 2020 21:55:49 +0800
Subject: [PATCH 10/31] Rename `verify_shard_transition_false_positives` to
 `verify_empty_shard_transition`

---
 specs/phase1/beacon-chain.md | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 4f4713f703..e536ad6ef8 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -66,7 +66,7 @@
         - [`process_crosslinks`](#process_crosslinks)
         - [`process_attestation`](#process_attestation)
       - [New Attester slashing processing](#new-attester-slashing-processing)
-    - [Shard transition false positives](#shard-transition-false-positives)
+    - [Verify empty shard transition](#verify-empty-shard-transition)
     - [Light client processing](#light-client-processing)
   - [Epoch transition](#epoch-transition)
     - [Custody game updates](#custody-game-updates)
@@ -671,7 +671,7 @@ def process_block(state: BeaconState, block: BeaconBlock) -> None:
     process_eth1_data(state, block.body)
     process_light_client_signatures(state, block.body)
     process_operations(state, block.body)
-    verify_shard_transition_false_positives(state, block.body)
+    verify_empty_shard_transition(state, block.body)
 ```
 
 #### Operations
@@ -943,11 +943,13 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
     assert slashed_any
 ```
 
-#### Shard transition false positives
+#### Verify empty shard transition
 
 ```python
-def verify_shard_transition_false_positives(state: BeaconState, block_body: BeaconBlockBody) -> None:
-    # Verify that a `shard_transition` in a block is empty if an attestation was not processed for it
+def verify_empty_shard_transition(state: BeaconState, block_body: BeaconBlockBody) -> None:
+    """
+    Verify that a `shard_transition` in a block is empty if an attestation was not processed for it.
+    """
     for shard in range(get_active_shard_count(state)):
         if state.shard_states[shard].slot != compute_previous_slot(state.slot):
             assert block_body.shard_transitions[shard] == ShardTransition()

From 7509ecb742173e0df6768d18fdc4d07686ae5184 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 28 May 2020 22:39:52 +0800
Subject: [PATCH 11/31] Add comments, minor refactoring

---
 specs/phase1/beacon-chain.md     | 75 ++++++++++++++++++--------------
 specs/phase1/shard-transition.md |  6 +--
 2 files changed, 44 insertions(+), 37 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 0ae4bae2b1..89dd6aaac2 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -64,7 +64,7 @@
         - [`apply_shard_transition`](#apply_shard_transition)
         - [`process_crosslink_for_shard`](#process_crosslink_for_shard)
         - [`process_crosslinks`](#process_crosslinks)
-        - [`process_attestation`](#process_attestation)
+        - [Updated `process_attestation`](#updated-process_attestation)
       - [New Attester slashing processing](#new-attester-slashing-processing)
     - [Shard transition false positives](#shard-transition-false-positives)
     - [Light client processing](#light-client-processing)
@@ -153,6 +153,7 @@ class PendingAttestation(Container):
     data: AttestationData
     inclusion_delay: Slot
     proposer_index: ValidatorIndex
+    # Phase 1
     crosslink_success: boolean
 ```
 
@@ -445,13 +446,13 @@ def compute_offset_slots(start_slot: Slot, end_slot: Slot) -> Sequence[Slot]:
 #### `compute_updated_gasprice`
 
 ```python
-def compute_updated_gasprice(prev_gasprice: Gwei, length: uint8) -> Gwei:
-    if length > TARGET_SHARD_BLOCK_SIZE:
-        delta = (prev_gasprice * (length - TARGET_SHARD_BLOCK_SIZE)
+def compute_updated_gasprice(prev_gasprice: Gwei, shard_block_length: uint8) -> Gwei:
+    if shard_block_length > TARGET_SHARD_BLOCK_SIZE:
+        delta = (prev_gasprice * (shard_block_length - TARGET_SHARD_BLOCK_SIZE)
                  // TARGET_SHARD_BLOCK_SIZE // GASPRICE_ADJUSTMENT_COEFFICIENT)
         return min(prev_gasprice + delta, MAX_GASPRICE)
     else:
-        delta = (prev_gasprice * (TARGET_SHARD_BLOCK_SIZE - length)
+        delta = (prev_gasprice * (TARGET_SHARD_BLOCK_SIZE - shard_block_length)
                  // TARGET_SHARD_BLOCK_SIZE // GASPRICE_ADJUSTMENT_COEFFICIENT)
         return max(prev_gasprice, MIN_GASPRICE + delta) - delta
 ```
@@ -477,9 +478,12 @@ def get_online_validator_indices(state: BeaconState) -> Set[ValidatorIndex]:
 
 ```python
 def get_shard_committee(beacon_state: BeaconState, epoch: Epoch, shard: Shard) -> Sequence[ValidatorIndex]:
+    """
+    Return the shard committee of the given ``epoch`` of the given ``shard``.
+    """
     source_epoch = epoch - epoch % SHARD_COMMITTEE_PERIOD
     if source_epoch >= SHARD_COMMITTEE_PERIOD:
-        source_epoch -= SHARD_COMMITTEE_PERIOD
+        source_epoch -= SHARD_COMMITTEE_PERIOD  # `SHARD_COMMITTEE_PERIOD` epochs lookahead
     active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
     seed = get_seed(beacon_state, source_epoch, DOMAIN_SHARD_COMMITTEE)
     active_shard_count = get_active_shard_count(beacon_state)
@@ -495,9 +499,12 @@ def get_shard_committee(beacon_state: BeaconState, epoch: Epoch, shard: Shard) -
 
 ```python
 def get_light_client_committee(beacon_state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
+    """
+    Return the light client committee that no more than ``TARGET_COMMITTEE_SIZE`` validators.
+    """
     source_epoch = epoch - epoch % LIGHT_CLIENT_COMMITTEE_PERIOD
     if source_epoch >= LIGHT_CLIENT_COMMITTEE_PERIOD:
-        source_epoch -= LIGHT_CLIENT_COMMITTEE_PERIOD
+        source_epoch -= LIGHT_CLIENT_COMMITTEE_PERIOD  # `LIGHT_CLIENT_COMMITTEE_PERIOD` epochs lookahead
     active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
     seed = get_seed(beacon_state, source_epoch, DOMAIN_LIGHT_CLIENT)
     return compute_committee(
@@ -554,7 +561,10 @@ def get_latest_slot_for_shard(state: BeaconState, shard: Shard) -> Slot:
 
 ```python
 def get_offset_slots(state: BeaconState, shard: Shard) -> Sequence[Slot]:
-    return compute_offset_slots(state.shard_states[shard].slot, state.slot)
+    """
+    Return the offset slots of the given ``shard`` between that latest included slot and current slot.
+    """
+    return compute_offset_slots(get_latest_slot_for_shard(state, shard), state.slot)
 ```
 
 ### Predicates
@@ -569,36 +579,38 @@ def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
     Check if ``indexed_attestation`` has valid indices and signature.
     """
     # Verify aggregate signature
-    all_pubkeys = []
-    all_signing_roots = []
     attestation = indexed_attestation.attestation
-    domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
     aggregation_bits = attestation.aggregation_bits
     if not any(aggregation_bits) or len(aggregation_bits) != len(indexed_attestation.committee):
         return False
 
+    domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
+    all_pubkeys = []
+    all_signing_roots = []
     if len(attestation.custody_bits_blocks) == 0:
         # fall back on phase0 behavior if there is no shard data.
-        for participant, abit in zip(indexed_attestation.committee, aggregation_bits):
-            if abit:
+        for participant, aggregation_bit in zip(indexed_attestation.committee, aggregation_bits):
+            if aggregation_bit:
                 all_pubkeys.append(state.validators[participant].pubkey)
         signing_root = compute_signing_root(indexed_attestation.attestation.data, domain)
         return bls.FastAggregateVerify(all_pubkeys, signing_root, signature=attestation.signature)
     else:
-        for i, custody_bits in enumerate(attestation.custody_bits_blocks):
+        for block_index, custody_bits in enumerate(attestation.custody_bits_blocks):
             assert len(custody_bits) == len(indexed_attestation.committee)
-            for participant, abit, cbit in zip(indexed_attestation.committee, aggregation_bits, custody_bits):
-                if abit:
+            for participant, aggregation_bit, custody_bit in zip(
+                indexed_attestation.committee, aggregation_bits, custody_bits
+            ):
+                if aggregation_bit:
                     all_pubkeys.append(state.validators[participant].pubkey)
                     # Note: only 2N distinct message hashes
                     attestation_wrapper = AttestationCustodyBitWrapper(
                         attestation_data_root=hash_tree_root(attestation.data),
-                        block_index=i,
-                        bit=cbit
+                        block_index=block_index,
+                        bit=custody_bit
                     )
                     all_signing_roots.append(compute_signing_root(attestation_wrapper, domain))
                 else:
-                    assert not cbit
+                    assert not custody_bit
         return bls.AggregateVerify(all_pubkeys, all_signing_roots, signature=attestation.signature)
 ```
 
@@ -767,22 +779,22 @@ def apply_shard_transition(state: BeaconState, shard: Shard, transition: ShardTr
     proposers = []
     prev_gasprice = state.shard_states[shard].gasprice
     shard_parent_root = state.shard_states[shard].latest_block_root
-    for i in range(len(offset_slots)):
+    for i, offset_slot in enumerate(offset_slots):
         shard_block_length = transition.shard_block_lengths[i]
         shard_state = transition.shard_states[i]
         # Verify correct calculation of gas prices and slots
         assert shard_state.gasprice == compute_updated_gasprice(prev_gasprice, shard_block_length)
-        assert shard_state.slot == offset_slots[i]
+        assert shard_state.slot == offset_slot
         # Collect the non-empty proposals result
         is_empty_proposal = shard_block_length == 0
         if not is_empty_proposal:
-            proposal_index = get_shard_proposer_index(state, offset_slots[i], shard)
+            proposal_index = get_shard_proposer_index(state, offset_slot, shard)
             # Reconstruct shard headers
             header = ShardBlockHeader(
                 shard_parent_root=shard_parent_root,
-                beacon_parent_root=get_block_root_at_slot(state, offset_slots[i]),
+                beacon_parent_root=get_block_root_at_slot(state, offset_slot),
                 proposer_index=proposal_index,
-                slot=offset_slots[i],
+                slot=offset_slot,
                 body_root=transition.shard_data_roots[i]
             )
             shard_parent_root = hash_tree_root(header)
@@ -872,13 +884,12 @@ def process_crosslinks(state: BeaconState,
     for committee_index in map(CommitteeIndex, range(committee_count)):
         shard = compute_shard_from_committee_index(state, committee_index, state.slot)
         # All attestations in the block for this committee/shard and current slot
-        shard_transition = shard_transitions[shard]
         shard_attestations = [
             attestation for attestation in attestations
             if is_shard_attestation(state, attestation, committee_index)
         ]
 
-        winning_root = process_crosslink_for_shard(state, committee_index, shard_transition, shard_attestations)
+        winning_root = process_crosslink_for_shard(state, committee_index, shard_transitions[shard], shard_attestations)
         if winning_root != Root():
             # Mark relevant pending attestations as creating a successful crosslink
             for pending_attestation in state.current_epoch_attestations:
@@ -886,7 +897,7 @@ def process_crosslinks(state: BeaconState,
                     pending_attestation.crosslink_success = True
 ```
 
-###### `process_attestation`
+###### Updated `process_attestation`
 
 ```python
 def process_attestation(state: BeaconState, attestation: Attestation) -> None:
@@ -910,11 +921,9 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
 ```python
 def get_indices_from_committee(
         committee: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE],
-        bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE]:
+        bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> Sequence[ValidatorIndex]:
     assert len(bits) == len(committee)
-    return List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE](
-        [validator_index for i, validator_index in enumerate(committee) if bits[i]]
-    )
+    return ([validator_index for i, validator_index in enumerate(committee) if bits[i]])
 ```
 
 ```python
@@ -1018,7 +1027,9 @@ def process_online_tracking(state: BeaconState) -> None:
 
 ```python
 def process_light_client_committee_updates(state: BeaconState) -> None:
-    # Update light client committees
+    """
+    Update light client committees.
+    """
     if get_current_epoch(state) % LIGHT_CLIENT_COMMITTEE_PERIOD == 0:
         state.current_light_committee = state.next_light_committee
         new_committee = get_light_client_committee(state, get_current_epoch(state) + LIGHT_CLIENT_COMMITTEE_PERIOD)
diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index da3aa648c8..1a82770665 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -268,12 +268,8 @@ def get_shard_transition(beacon_state: BeaconState,
                          shard: Shard,
                          shard_blocks: Sequence[SignedShardBlock]) -> ShardTransition:
     offset_slots = get_offset_slots(beacon_state, shard)
-    start_slot = offset_slots[0]
     proposals, shard_states, shard_data_roots = get_shard_state_transition_result(beacon_state, shard, shard_blocks)
 
-    assert len(proposals) > 0
-    assert len(shard_data_roots) > 0
-
     shard_block_lengths = []
     proposer_signatures = []
     for proposal in proposals:
@@ -287,7 +283,7 @@ def get_shard_transition(beacon_state: BeaconState,
         proposer_signature_aggregate = NO_SIGNATURE
 
     return ShardTransition(
-        start_slot=start_slot,
+        start_slot=offset_slots[0],
         shard_block_lengths=shard_block_lengths,
         shard_data_roots=shard_data_roots,
         shard_states=shard_states,

From 8ae7f5b6fa46c6423798ba56dee3c7192db8b232 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Fri, 29 May 2020 01:24:17 +0800
Subject: [PATCH 12/31] Refactor `is_valid_indexed_attestation`: extract
 `verify_attestation_custody`

---
 specs/phase1/beacon-chain.md | 57 +++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 21 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 89dd6aaac2..ee282f2030 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -52,6 +52,7 @@
     - [`get_latest_slot_for_shard`](#get_latest_slot_for_shard)
     - [`get_offset_slots`](#get_offset_slots)
   - [Predicates](#predicates)
+    - [`verify_attestation_custody`](#verify_attestation_custody)
     - [Updated `is_valid_indexed_attestation`](#updated-is_valid_indexed_attestation)
     - [`is_shard_attestation`](#is_shard_attestation)
     - [`is_winning_attestation`](#is_winning_attestation)
@@ -414,7 +415,7 @@ def unpack_compact_validator(compact_validator: uint64) -> Tuple[ValidatorIndex,
 ```python
 def committee_to_compact_committee(state: BeaconState, committee: Sequence[ValidatorIndex]) -> CompactCommittee:
     """
-    Given a state and a list of validator indices, outputs the CompactCommittee representing them.
+    Given a state and a list of validator indices, outputs the ``CompactCommittee`` representing them.
     """
     validators = [state.validators[i] for i in committee]
     compact_validators = [
@@ -569,6 +570,37 @@ def get_offset_slots(state: BeaconState, shard: Shard) -> Sequence[Slot]:
 
 ### Predicates
 
+#### `verify_attestation_custody`
+
+```python
+def verify_attestation_custody(state: BeaconState, indexed_attestation: IndexedAttestation) -> bool:
+    """
+    Check if ``indexed_attestation`` has valid signature against non-empty custody bits.
+    """
+    attestation = indexed_attestation.attestation
+    aggregation_bits = attestation.aggregation_bits
+    domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
+    all_pubkeys = []
+    all_signing_roots = []
+    for block_index, custody_bits in enumerate(attestation.custody_bits_blocks):
+        assert len(custody_bits) == len(indexed_attestation.committee)
+        for participant, aggregation_bit, custody_bit in zip(
+            indexed_attestation.committee, aggregation_bits, custody_bits
+        ):
+            if aggregation_bit:
+                all_pubkeys.append(state.validators[participant].pubkey)
+                # Note: only 2N distinct message hashes
+                attestation_wrapper = AttestationCustodyBitWrapper(
+                    attestation_data_root=hash_tree_root(attestation.data),
+                    block_index=block_index,
+                    bit=custody_bit,
+                )
+                all_signing_roots.append(compute_signing_root(attestation_wrapper, domain))
+            else:
+                assert not custody_bit
+    return bls.AggregateVerify(all_pubkeys, all_signing_roots, signature=attestation.signature)
+```
+
 #### Updated `is_valid_indexed_attestation`
 
 Note that this replaces the Phase 0 `is_valid_indexed_attestation`.
@@ -584,34 +616,17 @@ def is_valid_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
     if not any(aggregation_bits) or len(aggregation_bits) != len(indexed_attestation.committee):
         return False
 
-    domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
-    all_pubkeys = []
-    all_signing_roots = []
     if len(attestation.custody_bits_blocks) == 0:
         # fall back on phase0 behavior if there is no shard data.
+        domain = get_domain(state, DOMAIN_BEACON_ATTESTER, attestation.data.target.epoch)
+        all_pubkeys = []
         for participant, aggregation_bit in zip(indexed_attestation.committee, aggregation_bits):
             if aggregation_bit:
                 all_pubkeys.append(state.validators[participant].pubkey)
         signing_root = compute_signing_root(indexed_attestation.attestation.data, domain)
         return bls.FastAggregateVerify(all_pubkeys, signing_root, signature=attestation.signature)
     else:
-        for block_index, custody_bits in enumerate(attestation.custody_bits_blocks):
-            assert len(custody_bits) == len(indexed_attestation.committee)
-            for participant, aggregation_bit, custody_bit in zip(
-                indexed_attestation.committee, aggregation_bits, custody_bits
-            ):
-                if aggregation_bit:
-                    all_pubkeys.append(state.validators[participant].pubkey)
-                    # Note: only 2N distinct message hashes
-                    attestation_wrapper = AttestationCustodyBitWrapper(
-                        attestation_data_root=hash_tree_root(attestation.data),
-                        block_index=block_index,
-                        bit=custody_bit
-                    )
-                    all_signing_roots.append(compute_signing_root(attestation_wrapper, domain))
-                else:
-                    assert not custody_bit
-        return bls.AggregateVerify(all_pubkeys, all_signing_roots, signature=attestation.signature)
+        return verify_attestation_custody(state, indexed_attestation)
 ```
 
 #### `is_shard_attestation`

From bd9f983eeae34b11ebb84df2d000ab7f22ab3d34 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Fri, 29 May 2020 02:20:38 +0800
Subject: [PATCH 13/31] Minor fix

---
 specs/phase1/beacon-chain.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index ee282f2030..ce47ef5857 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -938,7 +938,7 @@ def get_indices_from_committee(
         committee: List[ValidatorIndex, MAX_VALIDATORS_PER_COMMITTEE],
         bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE]) -> Sequence[ValidatorIndex]:
     assert len(bits) == len(committee)
-    return ([validator_index for i, validator_index in enumerate(committee) if bits[i]])
+    return [validator_index for i, validator_index in enumerate(committee) if bits[i]]
 ```
 
 ```python

From b16e6d7a8623d6d90c90ea0fb64cc29a993952b5 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Fri, 29 May 2020 12:58:19 +0800
Subject: [PATCH 14/31] PR feedback from Danny

Co-authored-by: Danny Ryan <dannyjryan@gmail.com>
---
 specs/phase1/beacon-chain.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index e536ad6ef8..f087247f44 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -948,7 +948,7 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
 ```python
 def verify_empty_shard_transition(state: BeaconState, block_body: BeaconBlockBody) -> None:
     """
-    Verify that a `shard_transition` in a block is empty if an attestation was not processed for it.
+    Verify that ``shard_transitions`` are empty if a crosslink was not formed for the associated shard in this slot.
     """
     for shard in range(get_active_shard_count(state)):
         if state.shard_states[shard].slot != compute_previous_slot(state.slot):

From f70224b84e0e2eebf7e89ff36fc218ea217d3569 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Sat, 30 May 2020 03:09:42 +0800
Subject: [PATCH 15/31] Extract `compute_committee_source_epoch`

---
 specs/phase1/beacon-chain.md | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index ce47ef5857..0548688475 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -40,6 +40,7 @@
     - [`compute_shard_from_committee_index`](#compute_shard_from_committee_index)
     - [`compute_offset_slots`](#compute_offset_slots)
     - [`compute_updated_gasprice`](#compute_updated_gasprice)
+    - [`compute_committee_source_epoch`](#compute_committee_source_epoch)
   - [Beacon state accessors](#beacon-state-accessors)
     - [`get_active_shard_count`](#get_active_shard_count)
     - [`get_online_validator_indices`](#get_online_validator_indices)
@@ -458,6 +459,19 @@ def compute_updated_gasprice(prev_gasprice: Gwei, shard_block_length: uint8) ->
         return max(prev_gasprice, MIN_GASPRICE + delta) - delta
 ```
 
+#### `compute_committee_source_epoch`
+
+```python
+def compute_committee_source_epoch(epoch: Epoch, period: uint64) -> Epoch:
+    """
+    Return the source epoch for computing the committee.
+    """
+    source_epoch = epoch - epoch % period
+    if source_epoch >= period:
+        source_epoch -= period  # `period` epochs lookahead
+    return source_epoch
+```
+
 ### Beacon state accessors
 
 #### `get_active_shard_count`
@@ -482,9 +496,7 @@ def get_shard_committee(beacon_state: BeaconState, epoch: Epoch, shard: Shard) -
     """
     Return the shard committee of the given ``epoch`` of the given ``shard``.
     """
-    source_epoch = epoch - epoch % SHARD_COMMITTEE_PERIOD
-    if source_epoch >= SHARD_COMMITTEE_PERIOD:
-        source_epoch -= SHARD_COMMITTEE_PERIOD  # `SHARD_COMMITTEE_PERIOD` epochs lookahead
+    source_epoch = compute_committee_source_epoch(epoch, SHARD_COMMITTEE_PERIOD)
     active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
     seed = get_seed(beacon_state, source_epoch, DOMAIN_SHARD_COMMITTEE)
     active_shard_count = get_active_shard_count(beacon_state)
@@ -503,9 +515,7 @@ def get_light_client_committee(beacon_state: BeaconState, epoch: Epoch) -> Seque
     """
     Return the light client committee that no more than ``TARGET_COMMITTEE_SIZE`` validators.
     """
-    source_epoch = epoch - epoch % LIGHT_CLIENT_COMMITTEE_PERIOD
-    if source_epoch >= LIGHT_CLIENT_COMMITTEE_PERIOD:
-        source_epoch -= LIGHT_CLIENT_COMMITTEE_PERIOD  # `LIGHT_CLIENT_COMMITTEE_PERIOD` epochs lookahead
+    source_epoch = compute_committee_source_epoch(epoch, LIGHT_CLIENT_COMMITTEE_PERIOD)
     active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)
     seed = get_seed(beacon_state, source_epoch, DOMAIN_LIGHT_CLIENT)
     return compute_committee(

From cceeab265769cb9a39362fe81de42436b74e3f90 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Fri, 29 May 2020 03:14:43 +0800
Subject: [PATCH 16/31] Combine `process_crosslinks` and
 `verify_empty_shard_transition` into `process_shard_transitions`

---
 specs/phase1/beacon-chain.md                  | 24 +++++++++++++++----
 .../{crosslinks.py => shard_transitions.py}   |  8 +++----
 ...nk.py => test_process_shard_transition.py} |  4 ++--
 tests/generators/README.md                    |  2 +-
 4 files changed, 26 insertions(+), 12 deletions(-)
 rename tests/core/pyspec/eth2spec/test/helpers/{crosslinks.py => shard_transitions.py} (65%)
 rename tests/core/pyspec/eth2spec/test/phase_1/block_processing/{test_process_crosslink.py => test_process_shard_transition.py} (93%)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index f087247f44..8531602926 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -64,6 +64,7 @@
         - [`apply_shard_transition`](#apply_shard_transition)
         - [`process_crosslink_for_shard`](#process_crosslink_for_shard)
         - [`process_crosslinks`](#process_crosslinks)
+        - [`process_shard_transitions`](#process_shard_transitions)
         - [`process_attestation`](#process_attestation)
       - [New Attester slashing processing](#new-attester-slashing-processing)
     - [Verify empty shard transition](#verify-empty-shard-transition)
@@ -671,7 +672,6 @@ def process_block(state: BeaconState, block: BeaconBlock) -> None:
     process_eth1_data(state, block.body)
     process_light_client_signatures(state, block.body)
     process_operations(state, block.body)
-    verify_empty_shard_transition(state, block.body)
 ```
 
 #### Operations
@@ -695,7 +695,7 @@ def process_operations(state: BeaconState, body: BeaconBlockBody) -> None:
     # See custody game spec.
     process_custody_game_operations(state, body)
 
-    process_crosslinks(state, body.shard_transitions, body.attestations)
+    process_shard_transitions(state, body.shard_transitions, body.attestations)
 
     # TODO process_operations(body.shard_receipt_proofs, process_shard_receipt_proofs)
 ```
@@ -882,6 +882,18 @@ def process_crosslinks(state: BeaconState,
                     pending_attestation.crosslink_success = True
 ```
 
+###### `process_shard_transitions`
+
+```python
+def process_shard_transitions(state: BeaconState,
+                              shard_transitions: Sequence[ShardTransition],
+                              attestations: Sequence[Attestation]) -> None:
+    # Process crosslinks
+    process_crosslinks(state, shard_transitions, attestations)
+    # Verify the empty proposal shard states
+    assert verify_empty_shard_transition(state, shard_transitions)
+```
+
 ###### `process_attestation`
 
 ```python
@@ -893,7 +905,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
         data=attestation.data,
         inclusion_delay=state.slot - attestation.data.slot,
         proposer_index=get_beacon_proposer_index(state),
-        crosslink_success=False,  # To be filled in during process_crosslinks
+        crosslink_success=False,  # To be filled in during process_shard_transitions
     )
     if attestation.data.target.epoch == get_current_epoch(state):
         state.current_epoch_attestations.append(pending_attestation)
@@ -946,13 +958,15 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
 #### Verify empty shard transition
 
 ```python
-def verify_empty_shard_transition(state: BeaconState, block_body: BeaconBlockBody) -> None:
+def verify_empty_shard_transition(state: BeaconState, shard_transitions: Sequence[ShardTransition]) -> bool:
     """
     Verify that ``shard_transitions`` are empty if a crosslink was not formed for the associated shard in this slot.
     """
     for shard in range(get_active_shard_count(state)):
         if state.shard_states[shard].slot != compute_previous_slot(state.slot):
-            assert block_body.shard_transitions[shard] == ShardTransition()
+            if shard_transitions[shard] != ShardTransition():
+                return False
+    return True
 ```
 
 #### Light client processing
diff --git a/tests/core/pyspec/eth2spec/test/helpers/crosslinks.py b/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
similarity index 65%
rename from tests/core/pyspec/eth2spec/test/helpers/crosslinks.py
rename to tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
index ea5da89d96..4ac0ddcfb5 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/crosslinks.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
@@ -1,9 +1,9 @@
 from eth2spec.test.context import expect_assertion_error
 
 
-def run_crosslinks_processing(spec, state, shard_transitions, attestations, valid=True):
+def run_shard_transitions_processing(spec, state, shard_transitions, attestations, valid=True):
     """
-    Run ``process_attestation``, yielding:
+    Run ``process_shard_transitions``, yielding:
       - pre-state ('pre')
       - shard_transitions ('shard_transitions')
       - attestations ('attestations')
@@ -17,12 +17,12 @@ def run_crosslinks_processing(spec, state, shard_transitions, attestations, vali
 
     # If the attestation is invalid, processing is aborted, and there is no post-state.
     if not valid:
-        expect_assertion_error(lambda: spec.process_crosslinks(state, shard_transitions, attestations))
+        expect_assertion_error(lambda: spec.process_shard_transitions(state, shard_transitions, attestations))
         yield 'post', None
         return
 
     # process crosslinks
-    spec.process_crosslinks(state, shard_transitions, attestations)
+    spec.process_shard_transitions(state, shard_transitions, attestations)
 
     # yield post-state
     yield 'post', state
diff --git a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_crosslink.py b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_shard_transition.py
similarity index 93%
rename from tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_crosslink.py
rename to tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_shard_transition.py
index 1f066b3442..b4721da5ec 100644
--- a/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_crosslink.py
+++ b/tests/core/pyspec/eth2spec/test/phase_1/block_processing/test_process_shard_transition.py
@@ -4,7 +4,7 @@
     spec_state_test,
     always_bls,
 )
-from eth2spec.test.helpers.crosslinks import run_crosslinks_processing
+from eth2spec.test.helpers.shard_transitions import run_shard_transitions_processing
 from eth2spec.test.helpers.shard_block import (
     build_attestation_with_shard_transition,
     build_shard_block,
@@ -46,7 +46,7 @@ def run_basic_crosslink_tests(spec, state, target_len_offset_slot, valid=True):
     transition_to(spec, state, state.slot + target_len_offset_slot)
     pre_shard_state = state.shard_states[shard]
 
-    yield from run_crosslinks_processing(spec, state, shard_transitions, [attestation], valid=valid)
+    yield from run_shard_transitions_processing(spec, state, shard_transitions, [attestation], valid=valid)
 
     if valid:
         # After state transition,
diff --git a/tests/generators/README.md b/tests/generators/README.md
index 77a50606b5..9446551fb7 100644
--- a/tests/generators/README.md
+++ b/tests/generators/README.md
@@ -184,7 +184,7 @@ def create_provider(handler_name: str, tests_src, config_name: str) -> gen_typin
 
 if __name__ == "__main__":
     gen_runner.run_generator("epoch_processing", [
-        create_provider('crosslinks', test_process_crosslinks, 'minimal'),
+        create_provider('final_updates', test_process_final_updates, 'minimal'),
         ...
     ])
 

From 327deb40b276ecf1e8c180d2f2c33b4f5196483c Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Fri, 29 May 2020 03:20:36 +0800
Subject: [PATCH 17/31] Adjust function blocks

---
 specs/phase1/beacon-chain.md | 73 +++++++++++++++++++-----------------
 1 file changed, 38 insertions(+), 35 deletions(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 8531602926..d939d1c9f5 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -61,13 +61,14 @@
     - [Operations](#operations)
       - [New Attestation processing](#new-attestation-processing)
         - [`validate_attestation`](#validate_attestation)
+        - [Updated `process_attestation`](#updated-process_attestation)
+      - [Shard transition processing](#shard-transition-processing)
         - [`apply_shard_transition`](#apply_shard_transition)
         - [`process_crosslink_for_shard`](#process_crosslink_for_shard)
         - [`process_crosslinks`](#process_crosslinks)
+        - [`verify_empty_shard_transition`](#verify_empty_shard_transition)
         - [`process_shard_transitions`](#process_shard_transitions)
-        - [`process_attestation`](#process_attestation)
       - [New Attester slashing processing](#new-attester-slashing-processing)
-    - [Verify empty shard transition](#verify-empty-shard-transition)
     - [Light client processing](#light-client-processing)
   - [Epoch transition](#epoch-transition)
     - [Custody game updates](#custody-game-updates)
@@ -742,6 +743,27 @@ def validate_attestation(state: BeaconState, attestation: Attestation) -> None:
     assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
 ```
 
+###### Updated `process_attestation`
+
+```python
+def process_attestation(state: BeaconState, attestation: Attestation) -> None:
+    validate_attestation(state, attestation)
+    # Store pending attestation for epoch processing
+    pending_attestation = PendingAttestation(
+        aggregation_bits=attestation.aggregation_bits,
+        data=attestation.data,
+        inclusion_delay=state.slot - attestation.data.slot,
+        proposer_index=get_beacon_proposer_index(state),
+        crosslink_success=False,  # To be filled in during process_shard_transitions
+    )
+    if attestation.data.target.epoch == get_current_epoch(state):
+        state.current_epoch_attestations.append(pending_attestation)
+    else:
+        state.previous_epoch_attestations.append(pending_attestation)
+```
+
+##### Shard transition processing
+
 ###### `apply_shard_transition`
 
 ```python
@@ -882,6 +904,20 @@ def process_crosslinks(state: BeaconState,
                     pending_attestation.crosslink_success = True
 ```
 
+###### `verify_empty_shard_transition`
+
+```python
+def verify_empty_shard_transition(state: BeaconState, shard_transitions: Sequence[ShardTransition]) -> bool:
+    """
+    Verify that a `shard_transition` in a block is empty if an attestation was not processed for it.
+    """
+    for shard in range(get_active_shard_count(state)):
+        if state.shard_states[shard].slot != compute_previous_slot(state.slot):
+            if shard_transitions[shard] != ShardTransition():
+                return False
+    return True
+```
+
 ###### `process_shard_transitions`
 
 ```python
@@ -894,25 +930,6 @@ def process_shard_transitions(state: BeaconState,
     assert verify_empty_shard_transition(state, shard_transitions)
 ```
 
-###### `process_attestation`
-
-```python
-def process_attestation(state: BeaconState, attestation: Attestation) -> None:
-    validate_attestation(state, attestation)
-    # Store pending attestation for epoch processing
-    pending_attestation = PendingAttestation(
-        aggregation_bits=attestation.aggregation_bits,
-        data=attestation.data,
-        inclusion_delay=state.slot - attestation.data.slot,
-        proposer_index=get_beacon_proposer_index(state),
-        crosslink_success=False,  # To be filled in during process_shard_transitions
-    )
-    if attestation.data.target.epoch == get_current_epoch(state):
-        state.current_epoch_attestations.append(pending_attestation)
-    else:
-        state.previous_epoch_attestations.append(pending_attestation)
-```
-
 ##### New Attester slashing processing
 
 ```python
@@ -955,20 +972,6 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
     assert slashed_any
 ```
 
-#### Verify empty shard transition
-
-```python
-def verify_empty_shard_transition(state: BeaconState, shard_transitions: Sequence[ShardTransition]) -> bool:
-    """
-    Verify that ``shard_transitions`` are empty if a crosslink was not formed for the associated shard in this slot.
-    """
-    for shard in range(get_active_shard_count(state)):
-        if state.shard_states[shard].slot != compute_previous_slot(state.slot):
-            if shard_transitions[shard] != ShardTransition():
-                return False
-    return True
-```
-
 #### Light client processing
 
 ```python

From 437b2ebb90d3f26b2fb92d23792c560f38208603 Mon Sep 17 00:00:00 2001
From: Alex Stokes <r.alex.stokes@gmail.com>
Date: Fri, 29 May 2020 18:16:06 -0700
Subject: [PATCH 18/31] Update fork choice spec comment for clarity

I think this change more clearly specifies the intended behavior. Given the terseness of the spec's code representation, I think we should aim for as much clarity as possible.
---
 specs/phase0/fork-choice.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
index 4ed2733e1a..baf7b7b7b4 100644
--- a/specs/phase0/fork-choice.md
+++ b/specs/phase0/fork-choice.md
@@ -150,7 +150,7 @@ def get_ancestor(store: Store, root: Root, slot: Slot) -> Root:
     elif block.slot == slot:
         return root
     else:
-        # root is older than queried slot, thus a skip slot. Return earliest root prior to slot
+        # root is older than queried slot, thus a skip slot. Return most recent root prior to slot
         return root
 ```
 

From 33e115f8c65407357852f1605399bfaf79f933cb Mon Sep 17 00:00:00 2001
From: Jacek Sieka <jacek@status.im>
Date: Sat, 30 May 2020 20:59:12 +0200
Subject: [PATCH 19/31] Clean up remaining `[]` List syntax

..and use List[byte, 256] for error message
---
 specs/phase0/p2p-interface.md | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index 84db361c93..a77f1851a6 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -150,6 +150,7 @@ This section outlines constants that are used in this spec.
 | Name | Value | Description |
 |---|---|---|
 | `GOSSIP_MAX_SIZE` | `2**20` (= 1048576, 1 MiB) | The maximum allowed size of uncompressed gossip messages. |
+| `MAX_REQUEST_BLOCKS` | `2**10` (= 1024) | Maximum number of blocks in a single request |
 | `MAX_CHUNK_SIZE` | `2**20` (1048576, 1 MiB) | The maximum allowed size of uncompressed req/resp chunked responses. |
 | `TTFB_TIMEOUT` | `5s` | The maximum time to wait for first byte of request response (time-to-first-byte). |
 | `RESP_TIMEOUT` | `10s` | The maximum time for complete response transfer. |
@@ -391,11 +392,11 @@ The `ErrorMessage` schema is:
 
 ```
 (
-  error_message: Bytes32
+  error_message: List[byte, 256]
 )
 ```
 
-*Note*: By convention, the `error_message` is a sequence of bytes that can be interpreted as a UTF-8 string up to 32 bytes - a 0 byte shortens the string in this interpretation. Clients MUST treat as valid any bytes.
+*Note*: By convention, the `error_message` is a sequence of bytes that MAY be interpreted as a UTF-8 string (for debugging purposes). Clients MUST treat as valid any byte sequences.
 
 ### Encoding strategies
 
@@ -443,9 +444,9 @@ In case of an invalid input (header or payload), a reader MUST:
 
 All messages that contain only a single field MUST be encoded directly as the type of that field and MUST NOT be encoded as an SSZ container.
 
-Responses that are SSZ-lists (for example `[]SignedBeaconBlock`) send their
+Responses that are SSZ-lists (for example `List[SignedBeaconBlock, ...]`) send their
 constituents individually as `response_chunk`s. For example, the
-`[]SignedBeaconBlock` response type sends zero or more `response_chunk`s. Each _successful_ `response_chunk` contains a single `SignedBeaconBlock` payload.
+`List[SignedBeaconBlock, ...]` response type sends zero or more `response_chunk`s. Each _successful_ `response_chunk` contains a single `SignedBeaconBlock` payload.
 
 ### Messages
 
@@ -528,7 +529,7 @@ Request Content:
 Response Content:
 ```
 (
-  []SignedBeaconBlock
+  List[SignedBeaconBlock, MAX_REQUEST_BLOCKS]
 )
 ```
 
@@ -545,7 +546,7 @@ The response MUST consist of zero or more `response_chunk`. Each _successful_ `r
 
 Clients MUST keep a record of signed blocks seen since the since the start of the weak subjectivity period and MUST support serving requests of blocks up to their own `head_block_root`.
 
-Clients MUST respond with at least the first block that exists in the range, if they have it.
+Clients MUST respond with at least the first block that exists in the range, if they have it, and no more than `MAX_REQUEST_BLOCKS` blocks.
 
 The following blocks, where they exist, MUST be send in consecutive order.
 
@@ -568,7 +569,7 @@ Request Content:
 
 ```
 (
-  []Root
+  List[Root, MAX_REQUEST_BLOCKS]
 )
 ```
 
@@ -576,12 +577,14 @@ Response Content:
 
 ```
 (
-  []SignedBeaconBlock
+  List[SignedBeaconBlock, MAX_REQUEST_BLOCKS]
 )
 ```
 
 Requests blocks by block root (= `hash_tree_root(SignedBeaconBlock.message)`). The response is a list of `SignedBeaconBlock` whose length is less than or equal to the number of requested blocks. It may be less in the case that the responding peer is missing blocks.
 
+No more than `MAX_REQUEST_BLOCKS` may be requested at a time.
+
 `BeaconBlocksByRoot` is primarily used to recover recent blocks (e.g. when receiving a block or attestation whose parent is unknown).
 
 The request MUST be encoded as an SSZ-field.

From 6317bd68aa7476d82064daf70d7dbd71236ae3e1 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Mon, 1 Jun 2020 17:47:47 +0800
Subject: [PATCH 20/31] PR feedback from Danny

Co-authored-by: Danny Ryan <dannyjryan@gmail.com>
---
 specs/phase1/beacon-chain.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 6c792432f1..308af4ee31 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -515,7 +515,7 @@ def get_shard_committee(beacon_state: BeaconState, epoch: Epoch, shard: Shard) -
 ```python
 def get_light_client_committee(beacon_state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
     """
-    Return the light client committee that no more than ``TARGET_COMMITTEE_SIZE`` validators.
+    Return the light client committee of no more than ``TARGET_COMMITTEE_SIZE`` validators.
     """
     source_epoch = compute_committee_source_epoch(epoch, LIGHT_CLIENT_COMMITTEE_PERIOD)
     active_validator_indices = get_active_validator_indices(beacon_state, source_epoch)

From 2a218520a1338aca2601cd90ffe2d31f64475495 Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Mon, 1 Jun 2020 14:31:45 -0700
Subject: [PATCH 21/31] Tidying up `shard_state_transition`

---
 specs/phase1/shard-transition.md | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index ce6d289bd5..f9de34b317 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -71,21 +71,22 @@ def verify_shard_block_signature(beacon_state: BeaconState,
 def shard_state_transition(beacon_state: BeaconState,
                            shard_state: ShardState,
                            block: ShardBlock) -> None:
-    # Update shard state
+    """
+    Update ``shard_state`` with shard ``block`` and ``beacon_state`.
+    """
+    shard_state.slot = block.slot
     prev_gasprice = shard_state.gasprice
-    if len(block.body) == 0:
-        latest_block_root = shard_state.latest_block_root
-    else:
-        latest_block_root = hash_tree_root(block)
-
+    shard_state.gasprice = compute_updated_gasprice(prev_gasprice, len(block.body))
     shard_state.transition_digest = compute_shard_transition_digest(
         beacon_state,
         shard_state,
         block.beacon_parent_root,
         hash_tree_root(block.body),
     )
-    shard_state.gasprice = compute_updated_gasprice(prev_gasprice, len(block.body))
-    shard_state.slot = block.slot
+    if len(block.body) == 0:
+        latest_block_root = shard_state.latest_block_root
+    else:
+        latest_block_root = hash_tree_root(block)
     shard_state.latest_block_root = latest_block_root
 ```
 

From c6aac1650600407a832fa9646362873ebb785d72 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Tue, 2 Jun 2020 17:16:25 +1000
Subject: [PATCH 22/31] Reword fork choice comment

---
 specs/phase0/fork-choice.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
index baf7b7b7b4..3f1c20c0a5 100644
--- a/specs/phase0/fork-choice.md
+++ b/specs/phase0/fork-choice.md
@@ -285,7 +285,7 @@ def validate_on_attestation(store: Store, attestation: Attestation) -> None:
     # Attestations must not be for blocks in the future. If not, the attestation should not be considered
     assert store.blocks[attestation.data.beacon_block_root].slot <= attestation.data.slot
 
-    # FFG and LMD vote must be consistent with each other
+    # LMD vote must be consistent with FFG target
     target_slot = compute_start_slot_at_epoch(target.epoch)
     assert target.root == get_ancestor(store, attestation.data.beacon_block_root, target_slot)
 

From 2a125e8497c37b8685ba5478be254105df2542d3 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Tue, 2 Jun 2020 17:22:33 +1000
Subject: [PATCH 23/31] Update fork-choice.md

---
 specs/phase0/fork-choice.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
index 3f1c20c0a5..b9d8ecd3c3 100644
--- a/specs/phase0/fork-choice.md
+++ b/specs/phase0/fork-choice.md
@@ -285,7 +285,7 @@ def validate_on_attestation(store: Store, attestation: Attestation) -> None:
     # Attestations must not be for blocks in the future. If not, the attestation should not be considered
     assert store.blocks[attestation.data.beacon_block_root].slot <= attestation.data.slot
 
-    # LMD vote must be consistent with FFG target
+    # LMD vote must be consistent with FFG vote target
     target_slot = compute_start_slot_at_epoch(target.epoch)
     assert target.root == get_ancestor(store, attestation.data.beacon_block_root, target_slot)
 

From 24427947b17060623047fca2fbc0b49d8b636fe7 Mon Sep 17 00:00:00 2001
From: terence tsao <terence@prysmaticlabs.com>
Date: Tue, 2 Jun 2020 08:09:43 -0700
Subject: [PATCH 24/31] Moved transition_digest to last

---
 specs/phase1/shard-transition.md | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index f9de34b317..e6221a9805 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -77,17 +77,17 @@ def shard_state_transition(beacon_state: BeaconState,
     shard_state.slot = block.slot
     prev_gasprice = shard_state.gasprice
     shard_state.gasprice = compute_updated_gasprice(prev_gasprice, len(block.body))
+    if len(block.body) == 0:
+        latest_block_root = shard_state.latest_block_root
+    else:
+        latest_block_root = hash_tree_root(block)
+    shard_state.latest_block_root = latest_block_root
     shard_state.transition_digest = compute_shard_transition_digest(
         beacon_state,
         shard_state,
         block.beacon_parent_root,
         hash_tree_root(block.body),
     )
-    if len(block.body) == 0:
-        latest_block_root = shard_state.latest_block_root
-    else:
-        latest_block_root = hash_tree_root(block)
-    shard_state.latest_block_root = latest_block_root
 ```
 
 We have a pure function `get_post_shard_state` for describing the fraud proof verification and honest validator behavior.

From 34412130c5a8df907680649adbae58ae45f3c0bc Mon Sep 17 00:00:00 2001
From: Raw Pong Ghmoa <58883403+q9f@users.noreply.github.com>
Date: Mon, 1 Jun 2020 13:59:03 +0200
Subject: [PATCH 25/31] phase0: enable a tunable genesis time

---
 specs/phase0/beacon-chain.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/specs/phase0/beacon-chain.md b/specs/phase0/beacon-chain.md
index 1be32da445..e4de2d38b4 100644
--- a/specs/phase0/beacon-chain.md
+++ b/specs/phase0/beacon-chain.md
@@ -218,7 +218,7 @@ The following values are (non-configurable) constants used throughout the specif
 
 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
-| `MIN_GENESIS_DELAY` | `86400` | seconds | 1 day |
+| `GENESIS_DELAY` | `172800` | seconds | 2 days |
 | `SECONDS_PER_SLOT` | `12` | seconds | 12 seconds |
 | `SECONDS_PER_ETH1_BLOCK` | `14` | seconds | 14 seconds |
 | `MIN_ATTESTATION_INCLUSION_DELAY` | `2**0` (= 1) | slots | 12 seconds |
@@ -1137,7 +1137,7 @@ Before the Ethereum 2.0 genesis has been triggered, and for every Ethereum 1.0 b
 - `eth1_timestamp` is the Unix timestamp corresponding to `eth1_block_hash`
 - `deposits` is the sequence of all deposits, ordered chronologically, up to (and including) the block with hash `eth1_block_hash`
 
-Eth1 blocks must only be considered once they are at least `SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE` seconds old (i.e. `eth1_timestamp + SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE <= current_unix_time`). Due to this constraint, if `MIN_GENESIS_DELAY < SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE`, then the `genesis_time` can happen before the time/state is first known. Values should be configured to avoid this case.
+Eth1 blocks must only be considered once they are at least `SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE` seconds old (i.e. `eth1_timestamp + SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE <= current_unix_time`). Due to this constraint, if `GENESIS_DELAY < SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE`, then the `genesis_time` can happen before the time/state is first known. Values should be configured to avoid this case.
 
 ```python
 def initialize_beacon_state_from_eth1(eth1_block_hash: Bytes32,
@@ -1149,7 +1149,7 @@ def initialize_beacon_state_from_eth1(eth1_block_hash: Bytes32,
         epoch=GENESIS_EPOCH,
     )
     state = BeaconState(
-        genesis_time=eth1_timestamp - eth1_timestamp % MIN_GENESIS_DELAY + 2 * MIN_GENESIS_DELAY,
+        genesis_time=eth1_timestamp + GENESIS_DELAY,
         fork=fork,
         eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=len(deposits)),
         latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),

From b3f2d81ad5063f728c4620ed5a9435b5dfbe8853 Mon Sep 17 00:00:00 2001
From: Raw Pong Ghmoa <58883403+q9f@users.noreply.github.com>
Date: Mon, 1 Jun 2020 14:02:29 +0200
Subject: [PATCH 26/31] reflect changes in mainnet.yaml

---
 configs/mainnet.yaml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/configs/mainnet.yaml b/configs/mainnet.yaml
index 42845c235a..3631b7045f 100644
--- a/configs/mainnet.yaml
+++ b/configs/mainnet.yaml
@@ -76,8 +76,8 @@ BLS_WITHDRAWAL_PREFIX: 0x00
 
 # Time parameters
 # ---------------------------------------------------------------
-# 86400 seconds (1 day)
-MIN_GENESIS_DELAY: 86400
+# 172800 seconds (2 days)
+GENESIS_DELAY: 172800
 # 12 seconds
 SECONDS_PER_SLOT: 12
 # 2**0 (= 1) slots 12 seconds

From d5ed78e974aa97e22c4695d25f82165a5cc46310 Mon Sep 17 00:00:00 2001
From: Raw Pong Ghmoa <58883403+q9f@users.noreply.github.com>
Date: Mon, 1 Jun 2020 14:03:07 +0200
Subject: [PATCH 27/31] reflect changes in minimal.yaml

---
 configs/minimal.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configs/minimal.yaml b/configs/minimal.yaml
index d8e346ffab..5abf6c93c8 100644
--- a/configs/minimal.yaml
+++ b/configs/minimal.yaml
@@ -77,7 +77,7 @@ BLS_WITHDRAWAL_PREFIX: 0x00
 # Time parameters
 # ---------------------------------------------------------------
 # [customized] Faster to spin up testnets, but does not give validator reasonable warning time for genesis
-MIN_GENESIS_DELAY: 300
+GENESIS_DELAY: 300
 # [customized] Faster for testing purposes
 SECONDS_PER_SLOT: 6
 # 2**0 (= 1) slots 6 seconds

From 671fae6efe83e0fe7e0e1256d2c0199daf7c42ed Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Tue, 2 Jun 2020 11:09:42 -0600
Subject: [PATCH 28/31] change note about genesis delay in p2p spec to match
 new GENESIS_DELAY config value; fix tests

---
 specs/phase0/p2p-interface.md                                 | 2 +-
 .../core/pyspec/eth2spec/test/genesis/test_initialization.py  | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index a994b0c66d..e47fafed0f 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -1052,7 +1052,7 @@ discv5 uses ENRs and we will presumably need to:
 
 Although client software might very well be running locally prior to the solidification of the eth2 genesis state and block, clients cannot form valid ENRs prior to this point. ENRs contain `fork_digest` which utilizes the `genesis_validators_root` for a cleaner separation between chains so prior to knowing genesis, we cannot use `fork_digest` to cleanly find peers on our intended chain. Once genesis data is known, we can then form ENRs and safely find peers.
 
-When using an eth1 deposit contract for deposits, `fork_digest` will be known at least `MIN_GENESIS_DELAY` (24 hours in mainnet configuration) before `genesis_time`, providing ample time to find peers and form initial connections and gossip subnets prior to genesis.
+When using an eth1 deposit contract for deposits, `fork_digest` will be known `GENESIS_DELAY` (48hours in mainnet configuration) before `genesis_time`, providing ample time to find peers and form initial connections and gossip subnets prior to genesis.
 
 ## Compression/Encoding
 
diff --git a/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py b/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
index 8828213377..faade2d17e 100644
--- a/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
+++ b/tests/core/pyspec/eth2spec/test/genesis/test_initialization.py
@@ -21,7 +21,7 @@ def test_initialize_beacon_state_from_eth1(spec):
     # initialize beacon_state
     state = spec.initialize_beacon_state_from_eth1(eth1_block_hash, eth1_timestamp, deposits)
 
-    assert state.genesis_time == eth1_timestamp - eth1_timestamp % spec.MIN_GENESIS_DELAY + 2 * spec.MIN_GENESIS_DELAY
+    assert state.genesis_time == eth1_timestamp + spec.GENESIS_DELAY
     assert len(state.validators) == deposit_count
     assert state.eth1_data.deposit_root == deposit_root
     assert state.eth1_data.deposit_count == deposit_count
@@ -57,7 +57,7 @@ def test_initialize_beacon_state_some_small_balances(spec):
     # initialize beacon_state
     state = spec.initialize_beacon_state_from_eth1(eth1_block_hash, eth1_timestamp, deposits)
 
-    assert state.genesis_time == eth1_timestamp - eth1_timestamp % spec.MIN_GENESIS_DELAY + 2 * spec.MIN_GENESIS_DELAY
+    assert state.genesis_time == eth1_timestamp + spec.GENESIS_DELAY
     assert len(state.validators) == small_deposit_count
     assert state.eth1_data.deposit_root == deposit_root
     assert state.eth1_data.deposit_count == len(deposits)

From 06dfff022bf05f63e703e1f0d1031d530edf4fb4 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Tue, 2 Jun 2020 11:21:00 -0600
Subject: [PATCH 29/31] add comment about default of 0x00 for genesis finalized
 checkpoint in p2p spec

---
 specs/phase0/p2p-interface.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index a994b0c66d..c7d61d8f19 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -468,9 +468,9 @@ The fields are, as seen by the client at the time of sending the message:
 - `fork_digest`: The node's `ForkDigest` (`compute_fork_digest(current_fork_version, genesis_validators_root)`) where
     - `current_fork_version` is the fork version at the node's current epoch defined by the wall-clock time (not necessarily the epoch to which the node is sync)
     - `genesis_validators_root` is the static `Root` found in `state.genesis_validators_root`
-- `finalized_root`: `state.finalized_checkpoint.root` for the state corresponding to the head block.
+- `finalized_root`: `state.finalized_checkpoint.root` for the state corresponding to the head block (Note this defaults to `Root(b'\x00' * 32)` for the genesis finalized checkpoint).
 - `finalized_epoch`: `state.finalized_checkpoint.epoch` for the state corresponding to the head block.
-- `head_root`: The hash_tree_root root of the current head block.
+- `head_root`: The `hash_tree_root` root of the current head block.
 - `head_slot`: The slot of the block corresponding to the `head_root`.
 
 The dialing client MUST send a `Status` request upon connection.

From cf7b9993b5ea1124ddd87579dc27a78ebf092e92 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Tue, 2 Jun 2020 13:51:43 -0600
Subject: [PATCH 30/31] clarify `head_root` is for a `BeaconBlock`

Co-authored-by: Diederik Loerakker <proto@protolambda.com>
---
 specs/phase0/p2p-interface.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/specs/phase0/p2p-interface.md b/specs/phase0/p2p-interface.md
index c7d61d8f19..e98070b6f4 100644
--- a/specs/phase0/p2p-interface.md
+++ b/specs/phase0/p2p-interface.md
@@ -470,7 +470,7 @@ The fields are, as seen by the client at the time of sending the message:
     - `genesis_validators_root` is the static `Root` found in `state.genesis_validators_root`
 - `finalized_root`: `state.finalized_checkpoint.root` for the state corresponding to the head block (Note this defaults to `Root(b'\x00' * 32)` for the genesis finalized checkpoint).
 - `finalized_epoch`: `state.finalized_checkpoint.epoch` for the state corresponding to the head block.
-- `head_root`: The `hash_tree_root` root of the current head block.
+- `head_root`: The `hash_tree_root` root of the current head block (`BeaconBlock`).
 - `head_slot`: The slot of the block corresponding to the `head_root`.
 
 The dialing client MUST send a `Status` request upon connection.

From 314dea97a5018740c5166e4884777c936f5d5150 Mon Sep 17 00:00:00 2001
From: Danny Ryan <dannyjryan@gmail.com>
Date: Tue, 2 Jun 2020 17:26:26 -0600
Subject: [PATCH 31/31] bump VERSION.txt to 0.12.1

---
 tests/core/pyspec/eth2spec/VERSION.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/core/pyspec/eth2spec/VERSION.txt b/tests/core/pyspec/eth2spec/VERSION.txt
index d33c3a2128..aac2dacab4 100644
--- a/tests/core/pyspec/eth2spec/VERSION.txt
+++ b/tests/core/pyspec/eth2spec/VERSION.txt
@@ -1 +1 @@
-0.12.0
\ No newline at end of file
+0.12.1
\ No newline at end of file