From 4a46fb2a8a91a3389bfe20b22e5c4d8ee7f28f28 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Wed, 24 Jun 2020 18:08:26 +0800
Subject: [PATCH 1/4] Refactor phase 1 block tests a bit and add
 `shard_state_transition` tests

1. Refacotr phase1/sanity/test_blocks.py
2. Add phase1/sanity/test_shard_blocks.py for testing `verify_shard_block_message` and `verify_shard_block_signature`
---
 specs/phase1/beacon-chain.md                  |   2 +-
 specs/phase1/shard-transition.md              |  12 +-
 .../test/helpers/shard_transitions.py         |   5 +
 .../test_process_shard_transition.py          |  10 +-
 .../test/phase1/sanity/test_blocks.py         |  25 ++-
 .../test/phase1/sanity/test_shard_blocks.py   | 151 ++++++++++++++++++
 6 files changed, 190 insertions(+), 15 deletions(-)
 create mode 100644 tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py

diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index 5a5200c9e..36abac85f 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -1,4 +1,4 @@
-# Ethereum 2.0 Phase 1 -- The Beacon Chain for Shards
+# Ethereum 2.0 Phase 1 -- The Beacon Chain with Shards
 
 **Notice**: This document is a work-in-progress for researchers and implementers.
 
diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 05f986000..09e603c58 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -11,7 +11,9 @@
 - [Introduction](#introduction)
 - [Helper functions](#helper-functions)
   - [Shard block verification functions](#shard-block-verification-functions)
-- [Shard state transition](#shard-state-transition)
+    - [`verify_shard_block_message`](#verify_shard_block_message)
+    - [`verify_shard_block_signature`](#verify_shard_block_signature)
+- [Shard state transition function](#shard-state-transition-function)
 - [Fraud proofs](#fraud-proofs)
   - [Verifying the proof](#verifying-the-proof)
 
@@ -25,6 +27,8 @@ This document describes the shard transition function and fraud proofs as part o
 
 ### Shard block verification functions
 
+#### `verify_shard_block_message`
+
 ```python
 def verify_shard_block_message(beacon_parent_state: BeaconState,
                                shard_parent_state: ShardState,
@@ -49,6 +53,8 @@ def verify_shard_block_message(beacon_parent_state: BeaconState,
     return True
 ```
 
+#### `verify_shard_block_signature`
+
 ```python
 def verify_shard_block_signature(beacon_parent_state: BeaconState,
                                  signed_block: SignedShardBlock) -> bool:
@@ -58,7 +64,9 @@ def verify_shard_block_signature(beacon_parent_state: BeaconState,
     return bls.Verify(proposer.pubkey, signing_root, signed_block.signature)
 ```
 
-## Shard state transition
+## Shard state transition function
+
+The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(state, signed_block)`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
 
 ```python
 def shard_state_transition(shard_state: ShardState,
diff --git a/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py b/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
index d10d1ee7b..6e508e397 100644
--- a/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
+++ b/tests/core/pyspec/eth2spec/test/helpers/shard_transitions.py
@@ -35,3 +35,8 @@ def get_shard_transition_of_committee(spec, state, committee_index, shard_blocks
     shard = spec.compute_shard_from_committee_index(state, committee_index, state.slot)
     shard_transition = spec.get_shard_transition(state, shard, shard_blocks=shard_blocks)
     return shard_transition
+
+
+def is_full_crosslink(spec, state):
+    epoch = spec.compute_epoch_at_slot(state.slot)
+    return spec.get_committee_count_per_slot(state, epoch) >= spec.get_active_shard_count(state)
diff --git a/tests/core/pyspec/eth2spec/test/phase1/block_processing/test_process_shard_transition.py b/tests/core/pyspec/eth2spec/test/phase1/block_processing/test_process_shard_transition.py
index b14b836c0..866831686 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/block_processing/test_process_shard_transition.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/block_processing/test_process_shard_transition.py
@@ -8,7 +8,10 @@ from eth2spec.test.helpers.attestations import (
     get_valid_on_time_attestation,
     run_attestation_processing,
 )
-from eth2spec.test.helpers.shard_transitions import run_shard_transitions_processing
+from eth2spec.test.helpers.shard_transitions import (
+    run_shard_transitions_processing,
+    is_full_crosslink,
+)
 from eth2spec.test.helpers.shard_block import (
     build_shard_block,
     get_shard_transitions,
@@ -42,11 +45,6 @@ def get_attestations_and_shard_transitions(spec, state, shard_block_dict):
     return attestations, shard_transitions
 
 
-def is_full_crosslink(spec, state):
-    epoch = spec.compute_epoch_at_slot(state.slot)
-    return spec.get_committee_count_per_slot(state, epoch) >= spec.get_active_shard_count(state)
-
-
 def run_successful_crosslink_tests(spec, state, target_len_offset_slot):
     state, shard, target_shard_slot = get_initial_env(spec, state, target_len_offset_slot)
     init_slot = state.slot
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
index aa24bfc1e..3cb2fe6c0 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
@@ -9,15 +9,17 @@ from eth2spec.test.helpers.attestations import get_valid_on_time_attestation
 from eth2spec.test.helpers.block import build_empty_block
 from eth2spec.test.helpers.shard_block import (
     build_shard_block,
+    get_sample_shard_block_body,
     get_shard_transitions,
 )
+from eth2spec.test.helpers.shard_transitions import is_full_crosslink
 from eth2spec.test.helpers.state import state_transition_and_sign_block, transition_to_valid_shard_slot, transition_to
 
 
 def run_beacon_block_with_shard_blocks(spec, state, target_len_offset_slot, committee_index, shard, valid=True):
     transition_to(spec, state, state.slot + target_len_offset_slot)
 
-    body = b'\x56' * spec.MAX_SHARD_BLOCK_SIZE
+    body = get_sample_shard_block_body(spec, is_max=True)
     shard_block = build_shard_block(spec, state, shard, body=body, slot=state.slot, signed=True)
     shard_block_dict: Dict[spec.Shard, Sequence[spec.SignedShardBlock]] = {shard: [shard_block]}
 
@@ -40,13 +42,16 @@ def run_beacon_block_with_shard_blocks(spec, state, target_len_offset_slot, comm
     pre_gasprice = state.shard_states[shard].gasprice
     pre_shard_states = state.shard_states.copy()
     yield 'pre', state.copy()
-    yield 'block', beacon_block
-    state_transition_and_sign_block(spec, state, beacon_block)
-    if valid:
-        yield 'post', state
-    else:
+
+    if not valid:
+        state_transition_and_sign_block(spec, state, beacon_block, expect_fail=True)
+        yield 'block', beacon_block
         yield 'post', None
         return
+    else:
+        state_transition_and_sign_block(spec, state, beacon_block)
+        yield 'block', beacon_block
+        yield 'post', None
 
     for shard in range(spec.get_active_shard_count(state)):
         post_shard_state = state.shard_states[shard]
@@ -67,6 +72,10 @@ def run_beacon_block_with_shard_blocks(spec, state, target_len_offset_slot, comm
 @spec_state_test
 def test_process_beacon_block_with_normal_shard_transition(spec, state):
     # NOTE: this test is only for full crosslink (minimal config), not for mainnet
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
     state = transition_to_valid_shard_slot(spec, state)
 
     target_len_offset_slot = 1
@@ -81,6 +90,10 @@ def test_process_beacon_block_with_normal_shard_transition(spec, state):
 @spec_state_test
 def test_process_beacon_block_with_empty_proposal_transition(spec, state):
     # NOTE: this test is only for full crosslink (minimal config), not for mainnet
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
     state = transition_to_valid_shard_slot(spec, state)
 
     target_len_offset_slot = 1
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
new file mode 100644
index 000000000..40d7e0650
--- /dev/null
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
@@ -0,0 +1,151 @@
+from eth2spec.test.context import (
+    PHASE0,
+    always_bls,
+    expect_assertion_error,
+    spec_state_test,
+    with_all_phases_except,
+)
+from eth2spec.test.helpers.shard_block import (
+    build_shard_block,
+    sign_shard_block,
+)
+from eth2spec.test.helpers.shard_transitions import is_full_crosslink
+from eth2spec.test.helpers.state import transition_to_valid_shard_slot
+
+
+def run_shard_blocks(spec, shard_state, signed_shard_block,
+                     beacon_parent_state,
+                     validate=True, valid=True):
+    yield 'pre', shard_state.copy()
+    yield 'signed_shard_block', signed_shard_block
+    yield 'validate', validate
+    yield 'beacon_parent_state', beacon_parent_state
+
+    if validate is False:
+        beacon_parent_state = None
+
+    if not valid:
+        expect_assertion_error(lambda: spec.shard_state_transition(
+            shard_state, signed_shard_block, validate=validate, beacon_parent_state=beacon_parent_state)
+        )
+        yield 'post', None
+    else:
+        spec.shard_state_transition(shard_state, signed_shard_block,
+                                    validate=validate, beacon_parent_state=beacon_parent_state)
+        yield 'post', shard_state
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+@always_bls
+def test_valid_shard_block(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=True)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state)
+
+
+#
+# verify_shard_block_message
+#
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+def test_invalid_shard_parent_root(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=True)
+    signed_shard_block.message.shard_parent_root = b'\x12' * 32
+    sign_shard_block(spec, beacon_state, shard, signed_shard_block)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state, valid=False)
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+def test_invalid_beacon_parent_root(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=True)
+    signed_shard_block.message.beacon_parent_root = b'\x12' * 32
+    sign_shard_block(spec, beacon_state, shard, signed_shard_block)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state, valid=False)
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+def test_invalid_slot(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=True)
+    signed_shard_block.message.slot = beacon_state.slot + 1
+    proposer_index = spec.get_shard_proposer_index(beacon_state, signed_shard_block.message.slot, shard)
+    sign_shard_block(spec, beacon_state, shard, signed_shard_block, proposer_index=proposer_index)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state, valid=False)
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+def test_invalid_proposer_index(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=True)
+    active_validator_indices = spec.get_active_validator_indices(beacon_state, spec.get_current_epoch(beacon_state))
+    proposer_index = (
+        (spec.get_shard_proposer_index(beacon_state, signed_shard_block.message.slot, shard) + 1)
+        % len(active_validator_indices)
+    )
+    signed_shard_block.message.proposer_index = proposer_index
+    sign_shard_block(spec, beacon_state, shard, signed_shard_block, proposer_index=proposer_index)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state, valid=False)
+
+
+#
+# verify_shard_block_signature
+#
+
+
+@with_all_phases_except([PHASE0])
+@spec_state_test
+@always_bls
+def test_invalid_signature(spec, state):
+    if not is_full_crosslink(spec, state):
+        # skip
+        return
+
+    beacon_state = transition_to_valid_shard_slot(spec, state)
+    shard = 0
+    shard_state = beacon_state.shard_states[shard]
+    signed_shard_block = build_shard_block(spec, beacon_state, shard, slot=beacon_state.slot, signed=False)
+
+    yield from run_shard_blocks(spec, shard_state, signed_shard_block, beacon_state, valid=False)

From 661959c13ec422cbfb588d40f0cb57fd9ff5c5fa Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Wed, 24 Jun 2020 18:18:50 +0800
Subject: [PATCH 2/4] Add `process_shard_block` verification

---
 specs/phase1/shard-transition.md              |  7 ++----
 .../test/phase1/sanity/test_shard_blocks.py   | 22 +++++++++++++++----
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 09e603c58..1ca5a9ab8 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -92,11 +92,8 @@ def process_shard_block(shard_state: ShardState,
     prev_gasprice = shard_state.gasprice
     shard_block_length = len(block.body)
     shard_state.gasprice = compute_updated_gasprice(prev_gasprice, uint64(shard_block_length))
-    if shard_block_length == 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
+    if shard_block_length != 0:
+        shard_state.latest_block_root = hash_tree_root(block)
 ```
 
 ## Fraud proofs
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
index 40d7e0650..4d07f340a 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
@@ -16,7 +16,8 @@ from eth2spec.test.helpers.state import transition_to_valid_shard_slot
 def run_shard_blocks(spec, shard_state, signed_shard_block,
                      beacon_parent_state,
                      validate=True, valid=True):
-    yield 'pre', shard_state.copy()
+    pre_shard_state = shard_state.copy()
+    yield 'pre', pre_shard_state
     yield 'signed_shard_block', signed_shard_block
     yield 'validate', validate
     yield 'beacon_parent_state', beacon_parent_state
@@ -29,10 +30,23 @@ def run_shard_blocks(spec, shard_state, signed_shard_block,
             shard_state, signed_shard_block, validate=validate, beacon_parent_state=beacon_parent_state)
         )
         yield 'post', None
+        return
+
+    spec.shard_state_transition(shard_state, signed_shard_block,
+                                validate=validate, beacon_parent_state=beacon_parent_state)
+    yield 'post', shard_state
+
+    # Verify `process_shard_block`
+    block = signed_shard_block.message
+
+    assert shard_state.slot == block.slot
+
+    shard_block_length = len(block.body)
+    assert shard_state.gasprice == spec.compute_updated_gasprice(pre_shard_state.gasprice, shard_block_length)
+    if shard_block_length != 0:
+        shard_state.latest_block_root == block.hash_tree_root()
     else:
-        spec.shard_state_transition(shard_state, signed_shard_block,
-                                    validate=validate, beacon_parent_state=beacon_parent_state)
-        yield 'post', shard_state
+        shard_state.latest_block_root == pre_shard_state.latest_block_root
 
 
 @with_all_phases_except([PHASE0])

From 79b6bc616d1ac6c6e2aa6864b2354190fc47534a Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 25 Jun 2020 10:58:04 +0800
Subject: [PATCH 3/4] PR feedback from danny

---
 specs/phase1/shard-transition.md                          | 2 +-
 .../pyspec/eth2spec/test/phase1/sanity/test_blocks.py     | 8 ++++----
 .../eth2spec/test/phase1/sanity/test_shard_blocks.py      | 4 +---
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 1ca5a9ab8..7deaf9f09 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -66,7 +66,7 @@ def verify_shard_block_signature(beacon_parent_state: BeaconState,
 
 ## Shard state transition function
 
-The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(state, signed_block)`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
+The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(shard_state, signed_block)`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
 
 ```python
 def shard_state_transition(shard_state: ShardState,
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
index 3cb2fe6c0..2c391a660 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_blocks.py
@@ -48,10 +48,10 @@ def run_beacon_block_with_shard_blocks(spec, state, target_len_offset_slot, comm
         yield 'block', beacon_block
         yield 'post', None
         return
-    else:
-        state_transition_and_sign_block(spec, state, beacon_block)
-        yield 'block', beacon_block
-        yield 'post', None
+
+    state_transition_and_sign_block(spec, state, beacon_block)
+    yield 'block', beacon_block
+    yield 'post', state
 
     for shard in range(spec.get_active_shard_count(state)):
         post_shard_state = state.shard_states[shard]
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
index 4d07f340a..e8c5f91da 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
@@ -17,14 +17,12 @@ def run_shard_blocks(spec, shard_state, signed_shard_block,
                      beacon_parent_state,
                      validate=True, valid=True):
     pre_shard_state = shard_state.copy()
+
     yield 'pre', pre_shard_state
     yield 'signed_shard_block', signed_shard_block
     yield 'validate', validate
     yield 'beacon_parent_state', beacon_parent_state
 
-    if validate is False:
-        beacon_parent_state = None
-
     if not valid:
         expect_assertion_error(lambda: spec.shard_state_transition(
             shard_state, signed_shard_block, validate=validate, beacon_parent_state=beacon_parent_state)

From 2a7b5f7e68569416b55a4d6faa2dba85b0925e00 Mon Sep 17 00:00:00 2001
From: Hsiao-Wei Wang <hwwang156@gmail.com>
Date: Thu, 25 Jun 2020 11:14:25 +0800
Subject: [PATCH 4/4] PR feedback from Danny: nuke optional beacon_parent_state

---
 specs/phase1/shard-fork-choice.md                  |  4 +---
 specs/phase1/shard-transition.md                   | 14 +++++++-------
 specs/phase1/validator.md                          |  2 +-
 .../test/phase1/sanity/test_shard_blocks.py        | 12 ++++--------
 4 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/specs/phase1/shard-fork-choice.md b/specs/phase1/shard-fork-choice.md
index 8d64eb842..ba5bc2617 100644
--- a/specs/phase1/shard-fork-choice.md
+++ b/specs/phase1/shard-fork-choice.md
@@ -170,9 +170,7 @@ def on_shard_block(store: Store, shard_store: ShardStore, signed_shard_block: Si
 
     # Check the block is valid and compute the post-state
     shard_state = shard_parent_state.copy()
-    shard_state_transition(
-        shard_state, signed_shard_block,
-        validate=True, beacon_parent_state=beacon_parent_state)
+    shard_state_transition(shard_state, signed_shard_block, beacon_parent_state, validate_result=True)
 
     # Add new block to the store
     shard_store.blocks[hash_tree_root(shard_block)] = shard_block
diff --git a/specs/phase1/shard-transition.md b/specs/phase1/shard-transition.md
index 7deaf9f09..e273f2ddc 100644
--- a/specs/phase1/shard-transition.md
+++ b/specs/phase1/shard-transition.md
@@ -66,16 +66,16 @@ def verify_shard_block_signature(beacon_parent_state: BeaconState,
 
 ## Shard state transition function
 
-The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(shard_state, signed_block)`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
+The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(shard_state, signed_block, beacon_parent_state)`, where `beacon_parent_state` is the parent beacon state of the `signed_block`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
 
 ```python
 def shard_state_transition(shard_state: ShardState,
                            signed_block: SignedShardBlock,
-                           validate: bool = True,
-                           beacon_parent_state: Optional[BeaconState] = None) -> ShardState:
-    if validate:
-        assert beacon_parent_state is not None
-        assert verify_shard_block_message(beacon_parent_state, shard_state, signed_block.message)
+                           beacon_parent_state: BeaconState,
+                           validate_result: bool = True) -> ShardState:
+    assert verify_shard_block_message(beacon_parent_state, shard_state, signed_block.message)
+
+    if validate_result:
         assert verify_shard_block_signature(beacon_parent_state, signed_block)
 
     process_shard_block(shard_state, signed_block.message)
@@ -133,7 +133,7 @@ def is_valid_fraud_proof(beacon_state: BeaconState,
     else:
         shard_state = transition.shard_states[offset_index - 1]  # Not doing the actual state updates here.
 
-    shard_state_transition(shard_state, block, validate=False)
+    process_shard_block(shard_state, block.message)
     if shard_state != transition.shard_states[offset_index]:
         return True
 
diff --git a/specs/phase1/validator.md b/specs/phase1/validator.md
index 8b7ade60b..130765268 100644
--- a/specs/phase1/validator.md
+++ b/specs/phase1/validator.md
@@ -299,7 +299,7 @@ def get_shard_transition_fields(
             shard_block = SignedShardBlock(message=ShardBlock(slot=slot, shard=shard))
             shard_data_roots.append(Root())
         shard_state = shard_state.copy()
-        shard_state_transition(shard_state, shard_block, validate=False)
+        process_shard_block(shard_state, shard_block.message)
         shard_states.append(shard_state)
         shard_block_lengths.append(len(shard_block.message.body))
 
diff --git a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
index e8c5f91da..99696dd45 100644
--- a/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
+++ b/tests/core/pyspec/eth2spec/test/phase1/sanity/test_shard_blocks.py
@@ -13,25 +13,21 @@ from eth2spec.test.helpers.shard_transitions import is_full_crosslink
 from eth2spec.test.helpers.state import transition_to_valid_shard_slot
 
 
-def run_shard_blocks(spec, shard_state, signed_shard_block,
-                     beacon_parent_state,
-                     validate=True, valid=True):
+def run_shard_blocks(spec, shard_state, signed_shard_block, beacon_parent_state, valid=True):
     pre_shard_state = shard_state.copy()
 
     yield 'pre', pre_shard_state
     yield 'signed_shard_block', signed_shard_block
-    yield 'validate', validate
     yield 'beacon_parent_state', beacon_parent_state
 
     if not valid:
-        expect_assertion_error(lambda: spec.shard_state_transition(
-            shard_state, signed_shard_block, validate=validate, beacon_parent_state=beacon_parent_state)
+        expect_assertion_error(
+            lambda: spec.shard_state_transition(shard_state, signed_shard_block, beacon_parent_state)
         )
         yield 'post', None
         return
 
-    spec.shard_state_transition(shard_state, signed_shard_block,
-                                validate=validate, beacon_parent_state=beacon_parent_state)
+    spec.shard_state_transition(shard_state, signed_shard_block, beacon_parent_state)
     yield 'post', shard_state
 
     # Verify `process_shard_block`